docs: pageserver controller rfc

docs: sharding phase 1 RFC
clarifications
2026-02-01 01:30:38 +00:00 · 2023-09-29 18:24:24 +01:00 · 2023-09-29 18:20:13 +01:00 · 2023-09-27 10:38:52 +01:00 · 2023-09-27 10:38:52 +01:00 · 2023-09-27 10:38:41 +01:00
216 changed files with 16708 additions and 4668 deletions
--- a/.dockerignore
+++ b/.dockerignore
@@ -14,10 +14,12 @@
 !pgxn/
 !proxy/
 !safekeeper/
+!s3_scrubber/
 !storage_broker/
 !trace/
 !vendor/postgres-v14/
 !vendor/postgres-v15/
+!vendor/postgres-v16/
 !workspace_hack/
 !neon_local/
 !scripts/ninstall.sh
--- a/.github/actionlint.yml
+++ b/.github/actionlint.yml
@@ -0,0 +1,8 @@
+self-hosted-runner:
+  labels:
+    - gen3
+    - large
+    - small
+    - us-east-2
+config-variables:
+  - SLACK_UPCOMING_RELEASE_CHANNEL_ID
--- a/.github/actions/run-python-test-set/action.yml
+++ b/.github/actions/run-python-test-set/action.yml
@@ -70,6 +70,9 @@ runs:
        name: compatibility-snapshot-${{ inputs.build_type }}-pg${{ inputs.pg_version }}
        path: /tmp/compatibility_snapshot_pg${{ inputs.pg_version }}
        prefix: latest
+        # The lack of compatibility snapshot (for example, for the new Postgres version)
+        # shouldn't fail the whole job. Only relevant test should fail.
+        skip-if-does-not-exist: true

    - name: Checkout
      if: inputs.needs_postgres_source == 'true'
--- a/.github/workflows/actionlint.yml
+++ b/.github/workflows/actionlint.yml
@@ -0,0 +1,31 @@
+name: Lint GitHub Workflows
+
+on:
+  push:
+    branches:
+      - main
+      - release
+    paths:
+      - '.github/workflows/*.ya?ml'
+  pull_request:
+    paths:
+      - '.github/workflows/*.ya?ml'
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  actionlint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: reviewdog/action-actionlint@v1
+        env:
+          # SC2046 - Quote this to prevent word splitting. - https://www.shellcheck.net/wiki/SC2046
+          # SC2086 - Double quote to prevent globbing and word splitting. - https://www.shellcheck.net/wiki/SC2086
+          SHELLCHECK_OPTS: --exclude=SC2046,SC2086
+        with:
+          fail_on_error: true
+          filter_mode: nofilter
+          level: error
--- a/.github/workflows/approved-for-ci-run.yml
+++ b/.github/workflows/approved-for-ci-run.yml
@@ -2,7 +2,9 @@ name: Handle `approved-for-ci-run` label
 # This workflow helps to run CI pipeline for PRs made by external contributors (from forks).

 on:
-  pull_request:
+  pull_request_target:
+    branches:
+      - main
    types:
      # Default types that triggers a workflow ([1]):
      # - [1] https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request
@@ -14,42 +16,103 @@ on:
      # Actual magic happens here:
      - labeled

+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+
 env:
  GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
  PR_NUMBER: ${{ github.event.pull_request.number }}
+  BRANCH: "ci-run/pr-${{ github.event.pull_request.number }}"
+
+# No permission for GITHUB_TOKEN by default; the **minimal required** set of permissions should be granted in each job.
+permissions: {}
+
+defaults:
+  run:
+    shell: bash -euo pipefail {0}

 jobs:
  remove-label:
    # Remove `approved-for-ci-run` label if the workflow is triggered by changes in a PR.
    # The PR should be reviewed and labelled manually again.

-    runs-on: [ ubuntu-latest ]
+    permissions:
+      pull-requests: write # For `gh pr edit`

    if: |
      contains(fromJSON('["opened", "synchronize", "reopened", "closed"]'), github.event.action) &&
      contains(github.event.pull_request.labels.*.name, 'approved-for-ci-run')

+    runs-on: ubuntu-latest
+
    steps:
      - run: gh pr --repo "${GITHUB_REPOSITORY}" edit "${PR_NUMBER}" --remove-label "approved-for-ci-run"

-  create-branch:
-    # Create a local branch for an `approved-for-ci-run` labelled PR to run CI pipeline in it.
+  create-or-update-pr-for-ci-run:
+    # Create local PR for an `approved-for-ci-run` labelled PR to run CI pipeline in it.

-    runs-on: [ ubuntu-latest ]
+    permissions:
+      pull-requests: write # for `gh pr edit`
+      # For `git push` and `gh pr create` we use CI_ACCESS_TOKEN

    if: |
      github.event.action == 'labeled' &&
      contains(github.event.pull_request.labels.*.name, 'approved-for-ci-run')

+    runs-on: ubuntu-latest
+
    steps:
      - run: gh pr --repo "${GITHUB_REPOSITORY}" edit "${PR_NUMBER}" --remove-label "approved-for-ci-run"

      - uses: actions/checkout@v3
        with:
          ref: main
+          token: ${{ secrets.CI_ACCESS_TOKEN }}

      - run: gh pr checkout "${PR_NUMBER}"

-      - run: git checkout -b "ci-run/pr-${PR_NUMBER}"
+      - run: git checkout -b "${BRANCH}"

-      - run: git push --force origin "ci-run/pr-${PR_NUMBER}"
+      - run: git push --force origin "${BRANCH}"
+
+      - name: Create a Pull Request for CI run (if required)
+        env:
+          GH_TOKEN: ${{ secrets.CI_ACCESS_TOKEN }}
+        run: |
+          cat << EOF > body.md
+            This Pull Request is created automatically to run the CI pipeline for #${PR_NUMBER}
+
+            Please do not alter or merge/close it.
+
+            Feel free to review/comment/discuss the original PR #${PR_NUMBER}.
+          EOF
+
+          ALREADY_CREATED="$(gh pr --repo ${GITHUB_REPOSITORY} list --head ${BRANCH} --base main --json number --jq '.[].number')"
+          if [ -z "${ALREADY_CREATED}" ]; then
+            gh pr --repo "${GITHUB_REPOSITORY}" create --title "CI run for PR #${PR_NUMBER}" \
+                                                       --body-file "body.md" \
+                                                       --head "${BRANCH}" \
+                                                       --base "main" \
+                                                       --draft
+          fi
+
+  cleanup:
+    # Close PRs and delete branchs if the original PR is closed.
+
+    permissions:
+      contents: write # for `--delete-branch` flag in `gh pr close`
+      pull-requests: write # for `gh pr close`
+
+    if: |
+      github.event.action == 'closed' &&
+      github.event.pull_request.head.repo.full_name != github.repository
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Close PR and delete `ci-run/pr-${{ env.PR_NUMBER }}` branch
+        run: |
+          CLOSED="$(gh pr --repo ${GITHUB_REPOSITORY} list --head ${BRANCH} --json 'closed' --jq '.[].closed')"
+          if [ "${CLOSED}" == "false" ]; then
+            gh pr --repo "${GITHUB_REPOSITORY}" close "${BRANCH}" --delete-branch
+          fi
--- a/.github/workflows/benchmarking.yml
+++ b/.github/workflows/benchmarking.yml
@@ -117,6 +117,7 @@ jobs:
    outputs:
      pgbench-compare-matrix: ${{ steps.pgbench-compare-matrix.outputs.matrix }}
      olap-compare-matrix: ${{ steps.olap-compare-matrix.outputs.matrix }}
+      tpch-compare-matrix: ${{ steps.tpch-compare-matrix.outputs.matrix }}

    steps:
    - name: Generate matrix for pgbench benchmark
@@ -136,11 +137,11 @@ jobs:
        }'

        if [ "$(date +%A)" = "Saturday" ]; then
-          matrix=$(echo $matrix | jq '.include += [{ "platform": "rds-postgres", "db_size": "10gb"},
+          matrix=$(echo "$matrix" | jq '.include += [{ "platform": "rds-postgres", "db_size": "10gb"},
                                                   { "platform": "rds-aurora",   "db_size": "50gb"}]')
        fi

-        echo "matrix=$(echo $matrix | jq --compact-output '.')" >> $GITHUB_OUTPUT
+        echo "matrix=$(echo "$matrix" | jq --compact-output '.')" >> $GITHUB_OUTPUT

    - name: Generate matrix for OLAP benchmarks
      id: olap-compare-matrix
@@ -152,11 +153,30 @@ jobs:
        }'

        if [ "$(date +%A)" = "Saturday" ]; then
-          matrix=$(echo $matrix | jq '.include += [{ "platform": "rds-postgres" },
+          matrix=$(echo "$matrix" | jq '.include += [{ "platform": "rds-postgres" },
                                                   { "platform": "rds-aurora"   }]')
        fi

-        echo "matrix=$(echo $matrix | jq --compact-output '.')" >> $GITHUB_OUTPUT
+        echo "matrix=$(echo "$matrix" | jq --compact-output '.')" >> $GITHUB_OUTPUT
+
+    - name: Generate matrix for TPC-H benchmarks
+      id: tpch-compare-matrix
+      run: |
+        matrix='{
+          "platform": [
+            "neon-captest-reuse"
+          ],
+          "scale": [
+            "10"
+          ]
+        }'
+
+        if [ "$(date +%A)" = "Saturday" ]; then
+          matrix=$(echo "$matrix" | jq '.include += [{ "platform": "rds-postgres", "scale": "10" },
+                                                   { "platform": "rds-aurora",   "scale": "10" }]')
+        fi
+
+        echo "matrix=$(echo "$matrix" | jq --compact-output '.')" >> $GITHUB_OUTPUT

  pgbench-compare:
    needs: [ generate-matrices ]
@@ -233,7 +253,11 @@ jobs:

        echo "connstr=${CONNSTR}" >> $GITHUB_OUTPUT

-        psql ${CONNSTR} -c "SELECT version();"
+        QUERY="SELECT version();"
+        if [[ "${PLATFORM}" = "neon"* ]]; then
+          QUERY="${QUERY} SHOW neon.tenant_id; SHOW neon.timeline_id;"
+        fi
+        psql ${CONNSTR} -c "${QUERY}"

    - name: Benchmark init
      uses: ./.github/actions/run-python-test-set
@@ -358,7 +382,11 @@ jobs:

        echo "connstr=${CONNSTR}" >> $GITHUB_OUTPUT

-        psql ${CONNSTR} -c "SELECT version();"
+        QUERY="SELECT version();"
+        if [[ "${PLATFORM}" = "neon"* ]]; then
+          QUERY="${QUERY} SHOW neon.tenant_id; SHOW neon.timeline_id;"
+        fi
+        psql ${CONNSTR} -c "${QUERY}"

    - name: ClickBench benchmark
      uses: ./.github/actions/run-python-test-set
@@ -372,6 +400,7 @@ jobs:
        VIP_VAP_ACCESS_TOKEN: "${{ secrets.VIP_VAP_ACCESS_TOKEN }}"
        PERF_TEST_RESULT_CONNSTR: "${{ secrets.PERF_TEST_RESULT_CONNSTR }}"
        BENCHMARK_CONNSTR: ${{ steps.set-up-connstr.outputs.connstr }}
+        TEST_OLAP_SCALE: 10

    - name: Create Allure report
      if: ${{ !cancelled() }}
@@ -398,7 +427,7 @@ jobs:

    strategy:
      fail-fast: false
-      matrix: ${{ fromJson(needs.generate-matrices.outputs.olap-compare-matrix) }}
+      matrix: ${{ fromJson(needs.generate-matrices.outputs.tpch-compare-matrix) }}

    env:
      POSTGRES_DISTRIB_DIR: /tmp/neon/pg_install
@@ -407,6 +436,7 @@ jobs:
      BUILD_TYPE: remote
      SAVE_PERF_REPORT: ${{ github.event.inputs.save_perf_report || ( github.ref_name == 'main' ) }}
      PLATFORM: ${{ matrix.platform }}
+      TEST_OLAP_SCALE: ${{ matrix.scale }}

    runs-on: [ self-hosted, us-east-2, x64 ]
    container:
@@ -428,18 +458,17 @@ jobs:
        ${POSTGRES_DISTRIB_DIR}/v${DEFAULT_PG_VERSION}/bin/pgbench --version
        echo "${POSTGRES_DISTRIB_DIR}/v${DEFAULT_PG_VERSION}/bin" >> $GITHUB_PATH

-    - name: Set up Connection String
-      id: set-up-connstr
+    - name: Get Connstring Secret Name
      run: |
        case "${PLATFORM}" in
          neon-captest-reuse)
-            CONNSTR=${{ secrets.BENCHMARK_CAPTEST_TPCH_S10_CONNSTR }}
+            ENV_PLATFORM=CAPTEST_TPCH
            ;;
          rds-aurora)
-            CONNSTR=${{ secrets.BENCHMARK_RDS_AURORA_TPCH_S10_CONNSTR }}
+            ENV_PLATFORM=RDS_AURORA_TPCH
            ;;
          rds-postgres)
-            CONNSTR=${{ secrets.BENCHMARK_RDS_POSTGRES_TPCH_S10_CONNSTR }}
+            ENV_PLATFORM=RDS_AURORA_TPCH
            ;;
          *)
            echo >&2 "Unknown PLATFORM=${PLATFORM}. Allowed only 'neon-captest-reuse', 'rds-aurora', or 'rds-postgres'"
@@ -447,9 +476,21 @@ jobs:
            ;;
        esac

+        CONNSTR_SECRET_NAME="BENCHMARK_${ENV_PLATFORM}_S${TEST_OLAP_SCALE}_CONNSTR"
+        echo "CONNSTR_SECRET_NAME=${CONNSTR_SECRET_NAME}" >> $GITHUB_ENV
+
+    - name: Set up Connection String
+      id: set-up-connstr
+      run: |
+        CONNSTR=${{ secrets[env.CONNSTR_SECRET_NAME] }}
+
        echo "connstr=${CONNSTR}" >> $GITHUB_OUTPUT

-        psql ${CONNSTR} -c "SELECT version();"
+        QUERY="SELECT version();"
+        if [[ "${PLATFORM}" = "neon"* ]]; then
+          QUERY="${QUERY} SHOW neon.tenant_id; SHOW neon.timeline_id;"
+        fi
+        psql ${CONNSTR} -c "${QUERY}"

    - name: Run TPC-H benchmark
      uses: ./.github/actions/run-python-test-set
@@ -463,6 +504,7 @@ jobs:
        VIP_VAP_ACCESS_TOKEN: "${{ secrets.VIP_VAP_ACCESS_TOKEN }}"
        PERF_TEST_RESULT_CONNSTR: "${{ secrets.PERF_TEST_RESULT_CONNSTR }}"
        BENCHMARK_CONNSTR: ${{ steps.set-up-connstr.outputs.connstr }}
+        TEST_OLAP_SCALE: ${{ matrix.scale }}

    - name: Create Allure report
      if: ${{ !cancelled() }}
@@ -534,7 +576,11 @@ jobs:

        echo "connstr=${CONNSTR}" >> $GITHUB_OUTPUT

-        psql ${CONNSTR} -c "SELECT version();"
+        QUERY="SELECT version();"
+        if [[ "${PLATFORM}" = "neon"* ]]; then
+          QUERY="${QUERY} SHOW neon.tenant_id; SHOW neon.timeline_id;"
+        fi
+        psql ${CONNSTR} -c "${QUERY}"

    - name: Run user examples
      uses: ./.github/actions/run-python-test-set
--- a/.github/workflows/build_and_test.yml
+++ b/.github/workflows/build_and_test.yml
@@ -5,7 +5,6 @@ on:
    branches:
      - main
      - release
-      - ci-run/pr-*
  pull_request:

 defaults:
@@ -24,7 +23,30 @@ env:
  AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_KEY_DEV }}

 jobs:
+  check-permissions:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Disallow PRs from forks
+      if: |
+        github.event_name == 'pull_request' &&
+        github.event.pull_request.head.repo.full_name != github.repository
+
+      run: |
+        if [ "${{ contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.pull_request.author_association) }}" = "true" ]; then
+          MESSAGE="Please create a PR from a branch of ${GITHUB_REPOSITORY} instead of a fork"
+        else
+          MESSAGE="The PR should be reviewed and labelled with 'approved-for-ci-run' to trigger a CI run"
+        fi
+
+        echo >&2 "We don't run CI for PRs from forks"
+        echo >&2 "${MESSAGE}"
+
+        exit 1
+
+
  tag:
+    needs: [ check-permissions ]
    runs-on: [ self-hosted, gen3, small ]
    container: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/base:pinned
    outputs:
@@ -53,6 +75,7 @@ jobs:
        id: build-tag

  check-codestyle-python:
+    needs: [ check-permissions ]
    runs-on: [ self-hosted, gen3, small ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
@@ -85,6 +108,7 @@ jobs:
        run: poetry run mypy .

  check-codestyle-rust:
+    needs: [ check-permissions ]
    runs-on: [ self-hosted, gen3, large ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
@@ -151,6 +175,7 @@ jobs:
        run: cargo deny check

  build-neon:
+    needs: [ check-permissions ]
    runs-on: [ self-hosted, gen3, large ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
@@ -187,7 +212,7 @@ jobs:
          # Eventually it will be replaced by a regression test https://github.com/neondatabase/neon/pull/4603

          FAILED=false
-          for postgres in postgres-v14 postgres-v15; do
+          for postgres in postgres-v14 postgres-v15 postgres-v16; do
            expected=$(cat vendor/revisions.json | jq --raw-output '."'"${postgres}"'"')
            actual=$(git rev-parse "HEAD:vendor/${postgres}")
            if [ "${expected}" != "${actual}" ]; then
@@ -209,6 +234,10 @@ jobs:
        id: pg_v15_rev
        run: echo pg_rev=$(git rev-parse HEAD:vendor/postgres-v15) >> $GITHUB_OUTPUT

+      - name: Set pg 16 revision for caching
+        id: pg_v16_rev
+        run: echo pg_rev=$(git rev-parse HEAD:vendor/postgres-v16) >> $GITHUB_OUTPUT
+
      # Set some environment variables used by all the steps.
      #
      # CARGO_FLAGS is extra options to pass to "cargo build", "cargo test" etc.
@@ -229,10 +258,12 @@ jobs:
            cov_prefix=""
            CARGO_FLAGS="--locked --release"
          fi
-          echo "cov_prefix=${cov_prefix}" >> $GITHUB_ENV
-          echo "CARGO_FEATURES=${CARGO_FEATURES}" >> $GITHUB_ENV
-          echo "CARGO_FLAGS=${CARGO_FLAGS}" >> $GITHUB_ENV
-          echo "CARGO_HOME=${GITHUB_WORKSPACE}/.cargo" >> $GITHUB_ENV
+          {
+            echo "cov_prefix=${cov_prefix}"
+            echo "CARGO_FEATURES=${CARGO_FEATURES}"
+            echo "CARGO_FLAGS=${CARGO_FLAGS}"
+            echo "CARGO_HOME=${GITHUB_WORKSPACE}/.cargo"
+          } >> $GITHUB_ENV

      # Disabled for now
      # Don't include the ~/.cargo/registry/src directory. It contains just
@@ -267,6 +298,13 @@ jobs:
          path: pg_install/v15
          key: v1-${{ runner.os }}-${{ matrix.build_type }}-pg-${{ steps.pg_v15_rev.outputs.pg_rev }}-${{ hashFiles('Makefile') }}

+      - name: Cache postgres v16 build
+        id: cache_pg_16
+        uses: actions/cache@v3
+        with:
+          path: pg_install/v16
+          key: v1-${{ runner.os }}-${{ matrix.build_type }}-pg-${{ steps.pg_v16_rev.outputs.pg_rev }}-${{ hashFiles('Makefile') }}
+
      - name: Build postgres v14
        if: steps.cache_pg_14.outputs.cache-hit != 'true'
        run: mold -run make postgres-v14 -j$(nproc)
@@ -275,6 +313,10 @@ jobs:
        if: steps.cache_pg_15.outputs.cache-hit != 'true'
        run: mold -run make postgres-v15 -j$(nproc)

+      - name: Build postgres v16
+        if: steps.cache_pg_16.outputs.cache-hit != 'true'
+        run: mold -run make postgres-v16 -j$(nproc)
+
      - name: Build neon extensions
        run: mold -run make neon-pg-ext -j$(nproc)

@@ -348,17 +390,17 @@ jobs:
        uses: ./.github/actions/save-coverage-data

  regress-tests:
+    needs: [ check-permissions, build-neon ]
    runs-on: [ self-hosted, gen3, large ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
      # Default shared memory is 64mb
      options: --init --shm-size=512mb
-    needs: [ build-neon ]
    strategy:
      fail-fast: false
      matrix:
        build_type: [ debug, release ]
-        pg_version: [ v14, v15 ]
+        pg_version: [ v14, v15, v16 ]
    steps:
      - name: Checkout
        uses: actions/checkout@v3
@@ -386,12 +428,12 @@ jobs:
        uses: ./.github/actions/save-coverage-data

  benchmarks:
+    needs: [ check-permissions, build-neon ]
    runs-on: [ self-hosted, gen3, small ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
      # Default shared memory is 64mb
      options: --init --shm-size=512mb
-    needs: [ build-neon ]
    if: github.ref_name == 'main' || contains(github.event.pull_request.labels.*.name, 'run-benchmarks')
    strategy:
      fail-fast: false
@@ -418,12 +460,13 @@ jobs:
      # while coverage is currently collected for the debug ones

  create-test-report:
+    needs: [ check-permissions, regress-tests, coverage-report, benchmarks ]
+    if: ${{ !cancelled() && contains(fromJSON('["skipped", "success"]'), needs.check-permissions.result) }}
+
    runs-on: [ self-hosted, gen3, small ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
      options: --init
-    needs: [ regress-tests, benchmarks ]
-    if: ${{ !cancelled() }}

    steps:
      - uses: actions/checkout@v3
@@ -449,42 +492,40 @@ jobs:
              reportJsonUrl: "${{ steps.create-allure-report.outputs.report-json-url }}",
            }

+            const coverage = {
+              coverageUrl: "${{ needs.coverage-report.outputs.coverage-html }}",
+              summaryJsonUrl: "${{ needs.coverage-report.outputs.coverage-json }}",
+            }
+
            const script = require("./scripts/comment-test-report.js")
            await script({
              github,
              context,
              fetch,
              report,
+              coverage,
            })

  coverage-report:
+    needs: [ check-permissions, regress-tests ]
+
    runs-on: [ self-hosted, gen3, small ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/rust:pinned
      options: --init
-    needs: [ regress-tests ]
    strategy:
      fail-fast: false
      matrix:
        build_type: [ debug ]
+    outputs:
+        coverage-html: ${{ steps.upload-coverage-report-new.outputs.report-url }}
+        coverage-json: ${{ steps.upload-coverage-report-new.outputs.summary-json }}
    steps:
      - name: Checkout
        uses: actions/checkout@v3
        with:
          submodules: true
-          fetch-depth: 1
-
-#      Disabled for now
-#      - name: Restore cargo deps cache
-#        id: cache_cargo
-#        uses: actions/cache@v3
-#        with:
-#          path: |
-#            ~/.cargo/registry/
-#            !~/.cargo/registry/src
-#            ~/.cargo/git/
-#            target/
-#          key: v1-${{ runner.os }}-${{ matrix.build_type }}-cargo-${{ hashFiles('rust-toolchain.toml') }}-${{ hashFiles('Cargo.lock') }}
+          fetch-depth: 0

      - name: Get Neon artifact
        uses: ./.github/actions/download
@@ -527,13 +568,45 @@ jobs:
          REPORT_URL=https://${BUCKET}.s3.amazonaws.com/code-coverage/${COMMIT_SHA}/index.html
          echo "report-url=${REPORT_URL}" >> $GITHUB_OUTPUT

+      - name: Build coverage report NEW
+        id: upload-coverage-report-new
+        env:
+          BUCKET: neon-github-public-dev
+          COMMIT_SHA: ${{ github.event.pull_request.head.sha || github.sha }}
+        run: |
+          BASELINE="$(git merge-base HEAD origin/main)"
+          CURRENT="${COMMIT_SHA}"
+
+          cp /tmp/coverage/report/lcov.info ./${CURRENT}.info
+
+          GENHTML_ARGS="--ignore-errors path,unmapped,empty --synthesize-missing --demangle-cpp rustfilt --output-directory lcov-html ${CURRENT}.info"
+
+          # Use differential coverage if the baseline coverage exists.
+          # It can be missing if the coverage repoer wasn't uploaded yet or tests has failed on BASELINE commit.
+          if aws s3 cp --only-show-errors s3://${BUCKET}/code-coverage/${BASELINE}/lcov.info ./${BASELINE}.info; then
+            git diff ${BASELINE} ${CURRENT} -- '*.rs' > baseline-current.diff
+
+            GENHTML_ARGS="--baseline-file ${BASELINE}.info --diff-file baseline-current.diff ${GENHTML_ARGS}"
+          fi
+
+          genhtml ${GENHTML_ARGS}
+
+          aws s3 cp --only-show-errors --recursive ./lcov-html/ s3://${BUCKET}/code-coverage/${COMMIT_SHA}/lcov
+
+          REPORT_URL=https://${BUCKET}.s3.amazonaws.com/code-coverage/${COMMIT_SHA}/lcov/index.html
+          echo "report-url=${REPORT_URL}" >> $GITHUB_OUTPUT
+
+          REPORT_URL=https://${BUCKET}.s3.amazonaws.com/code-coverage/${COMMIT_SHA}/lcov/summary.json
+          echo "summary-json=${REPORT_URL}" >> $GITHUB_OUTPUT
+
      - uses: actions/github-script@v6
        env:
          REPORT_URL: ${{ steps.upload-coverage-report.outputs.report-url }}
+          REPORT_URL_NEW: ${{ steps.upload-coverage-report-new.outputs.report-url }}
          COMMIT_SHA: ${{ github.event.pull_request.head.sha || github.sha }}
        with:
          script: |
-            const { REPORT_URL, COMMIT_SHA } = process.env
+            const { REPORT_URL, REPORT_URL_NEW, COMMIT_SHA } = process.env

            await github.rest.repos.createCommitStatus({
              owner: context.repo.owner,
@@ -544,12 +617,21 @@ jobs:
              context: 'Code coverage report',
            })

+            await github.rest.repos.createCommitStatus({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              sha: `${COMMIT_SHA}`,
+              state: 'success',
+              target_url: `${REPORT_URL_NEW}`,
+              context: 'Code coverage report NEW',
+            })
+
  trigger-e2e-tests:
+    needs: [ check-permissions, promote-images, tag ]
    runs-on: [ self-hosted, gen3, small ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/base:pinned
      options: --init
-    needs: [ promote-images, tag ]
    steps:
      - name: Set PR's status to pending and request a remote CI test
        run: |
@@ -590,8 +672,8 @@ jobs:
            }"

  neon-image:
+    needs: [ check-permissions, tag ]
    runs-on: [ self-hosted, gen3, large ]
-    needs: [ tag ]
    container: gcr.io/kaniko-project/executor:v1.9.2-debug
    defaults:
      run:
@@ -638,7 +720,7 @@ jobs:

  compute-tools-image:
    runs-on: [ self-hosted, gen3, large ]
-    needs: [ tag ]
+    needs: [ check-permissions, tag ]
    container: gcr.io/kaniko-project/executor:v1.9.2-debug
    defaults:
      run:
@@ -683,17 +765,17 @@ jobs:
        run: rm -rf ~/.ecr

  compute-node-image:
+    needs: [ check-permissions, tag ]
    runs-on: [ self-hosted, gen3, large ]
    container:
      image: gcr.io/kaniko-project/executor:v1.9.2-debug
      # Workaround for "Resolving download.osgeo.org (download.osgeo.org)... failed: Temporary failure in name resolution.""
      # Should be prevented by https://github.com/neondatabase/neon/issues/4281
      options: --add-host=download.osgeo.org:140.211.15.30
-    needs: [ tag ]
    strategy:
      fail-fast: false
      matrix:
-        version: [ v14, v15 ]
+        version: [ v14, v15, v16 ]
    defaults:
      run:
        shell: sh -eu {0}
@@ -742,17 +824,17 @@ jobs:
        run: rm -rf ~/.ecr

  vm-compute-node-image:
+    needs: [ check-permissions, tag, compute-node-image ]
    runs-on: [ self-hosted, gen3, large ]
-    needs: [ tag, compute-node-image ]
    strategy:
      fail-fast: false
      matrix:
-        version: [ v14, v15 ]
+        version: [ v14, v15, v16 ]
    defaults:
      run:
        shell: sh -eu {0}
    env:
-      VM_BUILDER_VERSION: v0.17.5
+      VM_BUILDER_VERSION: v0.17.11

    steps:
      - name: Checkout
@@ -784,7 +866,7 @@ jobs:
          docker push 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-${{ matrix.version }}:${{needs.tag.outputs.build-tag}}

  test-images:
-    needs: [ tag, neon-image, compute-node-image, compute-tools-image ]
+    needs: [ check-permissions, tag, neon-image, compute-node-image, compute-tools-image ]
    runs-on: [ self-hosted, gen3, small ]

    steps:
@@ -827,8 +909,8 @@ jobs:
          docker compose -f ./docker-compose/docker-compose.yml down

  promote-images:
+    needs: [ check-permissions, tag, test-images, vm-compute-node-image ]
    runs-on: [ self-hosted, gen3, small ]
-    needs: [ tag, test-images, vm-compute-node-image ]
    container: golang:1.19-bullseye
    # Don't add if-condition here.
    # The job should always be run because we have dependant other jobs that shouldn't be skipped
@@ -848,6 +930,7 @@ jobs:
        run: |
          crane pull 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v14:${{needs.tag.outputs.build-tag}} vm-compute-node-v14
          crane pull 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v15:${{needs.tag.outputs.build-tag}} vm-compute-node-v15
+          crane pull 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v16:${{needs.tag.outputs.build-tag}} vm-compute-node-v16

      - name: Add latest tag to images
        if: |
@@ -860,6 +943,8 @@ jobs:
          crane tag 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v14:${{needs.tag.outputs.build-tag}} latest
          crane tag 369495373322.dkr.ecr.eu-central-1.amazonaws.com/compute-node-v15:${{needs.tag.outputs.build-tag}} latest
          crane tag 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v15:${{needs.tag.outputs.build-tag}} latest
+          crane tag 369495373322.dkr.ecr.eu-central-1.amazonaws.com/compute-node-v16:${{needs.tag.outputs.build-tag}} latest
+          crane tag 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v16:${{needs.tag.outputs.build-tag}} latest

      - name: Push images to production ECR
        if: |
@@ -872,6 +957,8 @@ jobs:
          crane copy 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v14:${{needs.tag.outputs.build-tag}} 093970136003.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v14:latest
          crane copy 369495373322.dkr.ecr.eu-central-1.amazonaws.com/compute-node-v15:${{needs.tag.outputs.build-tag}} 093970136003.dkr.ecr.eu-central-1.amazonaws.com/compute-node-v15:latest
          crane copy 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v15:${{needs.tag.outputs.build-tag}} 093970136003.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v15:latest
+          crane copy 369495373322.dkr.ecr.eu-central-1.amazonaws.com/compute-node-v16:${{needs.tag.outputs.build-tag}} 093970136003.dkr.ecr.eu-central-1.amazonaws.com/compute-node-v16:latest
+          crane copy 369495373322.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v16:${{needs.tag.outputs.build-tag}} 093970136003.dkr.ecr.eu-central-1.amazonaws.com/vm-compute-node-v16:latest

      - name: Configure Docker Hub login
        run: |
@@ -883,6 +970,7 @@ jobs:
        run: |
          crane push vm-compute-node-v14 neondatabase/vm-compute-node-v14:${{needs.tag.outputs.build-tag}}
          crane push vm-compute-node-v15 neondatabase/vm-compute-node-v15:${{needs.tag.outputs.build-tag}}
+          crane push vm-compute-node-v16 neondatabase/vm-compute-node-v16:${{needs.tag.outputs.build-tag}}

      - name: Push latest tags to Docker Hub
        if: |
@@ -895,21 +983,19 @@ jobs:
          crane tag neondatabase/vm-compute-node-v14:${{needs.tag.outputs.build-tag}} latest
          crane tag neondatabase/compute-node-v15:${{needs.tag.outputs.build-tag}} latest
          crane tag neondatabase/vm-compute-node-v15:${{needs.tag.outputs.build-tag}} latest
+          crane tag neondatabase/compute-node-v16:${{needs.tag.outputs.build-tag}} latest
+          crane tag neondatabase/vm-compute-node-v16:${{needs.tag.outputs.build-tag}} latest

      - name: Cleanup ECR folder
        run: rm -rf ~/.ecr

-  build-private-extensions:
-    runs-on: [ self-hosted, gen3, small ]
-    container:
-      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/base:pinned
-      options: --init
-    needs: [ tag ]
+  trigger-custom-extensions-build-and-wait:
+    needs: [ check-permissions, tag ]
+    runs-on: ubuntu-latest
    steps:
      - name: Set PR's status to pending and request a remote CI test
        run: |
-          COMMIT_SHA=${{ github.event.pull_request.head.sha }}
-          COMMIT_SHA=${COMMIT_SHA:-${{ github.sha }}}
+          COMMIT_SHA=${{ github.event.pull_request.head.sha || github.sha }}
          REMOTE_REPO="${{ github.repository_owner }}/build-custom-extensions"

          curl -f -X POST \
@@ -939,11 +1025,50 @@ jobs:
              }
            }"

+      - name: Wait for extension build to finish
+        env:
+          GH_TOKEN: ${{ secrets.CI_ACCESS_TOKEN }}
+        run: |
+          TIMEOUT=1800 # 30 minutes, usually it takes ~2-3 minutes, but if runners are busy, it might take longer
+          INTERVAL=15 # try each N seconds
+
+          last_status="" # a variable to carry the last status of the "build-and-upload-extensions" context
+
+          for ((i=0; i <= TIMEOUT; i+=INTERVAL)); do
+            sleep $INTERVAL
+
+            # Get statuses for the latest commit in the PR / branch
+            gh api \
+              -H "Accept: application/vnd.github+json" \
+              -H "X-GitHub-Api-Version: 2022-11-28" \
+              "/repos/${{ github.repository }}/statuses/${{ github.event.pull_request.head.sha || github.sha }}" > statuses.json
+
+            # Get the latest status for the "build-and-upload-extensions" context
+            last_status=$(jq --raw-output '[.[] | select(.context == "build-and-upload-extensions")] | sort_by(.created_at)[-1].state' statuses.json)
+            if [ "${last_status}" = "pending" ]; then
+              # Extension build is still in progress.
+              continue
+            elif [ "${last_status}" = "success" ]; then
+              # Extension build is successful.
+              exit 0
+            else
+              # Status is neither "pending" nor "success", exit the loop and fail the job.
+              break
+            fi
+          done
+
+          # Extension build failed, print `statuses.json` for debugging and fail the job.
+          jq '.' statuses.json
+
+          echo >&2 "Status of extension build is '${last_status}' != 'success'"
+          exit 1
+
  deploy:
+    needs: [ check-permissions, promote-images, tag, regress-tests, trigger-custom-extensions-build-and-wait ]
+    if: ( github.ref_name == 'main' || github.ref_name == 'release' ) && github.event_name != 'workflow_dispatch'
+
    runs-on: [ self-hosted, gen3, small ]
    container: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/ansible:latest
-    needs: [ promote-images, tag, regress-tests ]
-    if: ( github.ref_name == 'main' || github.ref_name == 'release' ) && github.event_name != 'workflow_dispatch'
    steps:
      - name: Fix git ownership
        run: |
@@ -966,8 +1091,9 @@ jobs:
          GH_TOKEN: ${{ secrets.CI_ACCESS_TOKEN }}
        run: |
          if [[ "$GITHUB_REF_NAME" == "main" ]]; then
-            gh workflow --repo neondatabase/aws run deploy-dev.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}}
+            gh workflow --repo neondatabase/aws run deploy-dev.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}} -f deployPreprodRegion=false
          elif [[ "$GITHUB_REF_NAME" == "release" ]]; then
+            gh workflow --repo neondatabase/aws run deploy-dev.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}} -f deployPreprodRegion=true
            gh workflow --repo neondatabase/aws run deploy-prod.yml --ref main -f branch=main -f dockerTag=${{needs.tag.outputs.build-tag}} -f disclamerAcknowledged=true
          else
            echo "GITHUB_REF_NAME (value '$GITHUB_REF_NAME') is not set to either 'main' or 'release'"
@@ -981,20 +1107,35 @@ jobs:
          # Retry script for 5XX server errors: https://github.com/actions/github-script#retries
          retries: 5
          script: |
-            github.rest.git.createRef({
+            await github.rest.git.createRef({
              owner: context.repo.owner,
              repo: context.repo.repo,
              ref: "refs/tags/${{ needs.tag.outputs.build-tag }}",
              sha: context.sha,
            })

+      - name: Create GitHub release
+        if: github.ref_name == 'release'
+        uses: actions/github-script@v6
+        with:
+          # Retry script for 5XX server errors: https://github.com/actions/github-script#retries
+          retries: 5
+          script: |
+            await github.rest.repos.createRelease({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              tag_name: "${{ needs.tag.outputs.build-tag }}",
+              generate_release_notes: true,
+            })
+
  promote-compatibility-data:
+    needs: [ check-permissions, promote-images, tag, regress-tests ]
+    if: github.ref_name == 'release'
+
    runs-on: [ self-hosted, gen3, small ]
    container:
      image: 369495373322.dkr.ecr.eu-central-1.amazonaws.com/base:pinned
      options: --init
-    needs: [ promote-images, tag, regress-tests ]
-    if: github.ref_name == 'release' && github.event_name != 'workflow_dispatch'
    steps:
      - name: Promote compatibility snapshot for the release
        env:
@@ -1002,7 +1143,7 @@ jobs:
          PREFIX: artifacts/latest
        run: |
          # Update compatibility snapshot for the release
-          for pg_version in v14 v15; do
+          for pg_version in v14 v15 v16; do
            for build_type in debug release; do
              OLD_FILENAME=compatibility-snapshot-${build_type}-pg${pg_version}-${GITHUB_RUN_ID}.tar.zst
              NEW_FILENAME=compatibility-snapshot-${build_type}-pg${pg_version}.tar.zst
--- a/.github/workflows/neon_extra_builds.yml
+++ b/.github/workflows/neon_extra_builds.yml
@@ -4,7 +4,6 @@ on:
  push:
    branches:
      - main
-      - ci-run/pr-*
  pull_request:

 defaults:
@@ -39,7 +38,7 @@ jobs:
          fetch-depth: 1

      - name: Install macOS postgres dependencies
-        run: brew install flex bison openssl protobuf
+        run: brew install flex bison openssl protobuf icu4c pkg-config

      - name: Set pg 14 revision for caching
        id: pg_v14_rev
@@ -49,6 +48,10 @@ jobs:
        id: pg_v15_rev
        run: echo pg_rev=$(git rev-parse HEAD:vendor/postgres-v15) >> $GITHUB_OUTPUT

+      - name: Set pg 16 revision for caching
+        id: pg_v16_rev
+        run: echo pg_rev=$(git rev-parse HEAD:vendor/postgres-v16) >> $GITHUB_OUTPUT
+
      - name: Cache postgres v14 build
        id: cache_pg_14
        uses: actions/cache@v3
@@ -63,6 +66,13 @@ jobs:
          path: pg_install/v15
          key: v1-${{ runner.os }}-${{ env.BUILD_TYPE }}-pg-${{ steps.pg_v15_rev.outputs.pg_rev }}-${{ hashFiles('Makefile') }}

+      - name: Cache postgres v16 build
+        id: cache_pg_16
+        uses: actions/cache@v3
+        with:
+          path: pg_install/v16
+          key: v1-${{ runner.os }}-${{ env.BUILD_TYPE }}-pg-${{ steps.pg_v16_rev.outputs.pg_rev }}-${{ hashFiles('Makefile') }}
+
      - name: Set extra env for macOS
        run: |
          echo 'LDFLAGS=-L/usr/local/opt/openssl@3/lib' >> $GITHUB_ENV
@@ -86,6 +96,10 @@ jobs:
        if: steps.cache_pg_15.outputs.cache-hit != 'true'
        run: make postgres-v15 -j$(nproc)

+      - name: Build postgres v16
+        if: steps.cache_pg_16.outputs.cache-hit != 'true'
+        run: make postgres-v16 -j$(nproc)
+
      - name: Build neon extensions
        run: make neon-pg-ext -j$(nproc)

--- a/.github/workflows/release-notify.yml
+++ b/.github/workflows/release-notify.yml
@@ -0,0 +1,29 @@
+name: Notify Slack channel about upcoming release
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.number }}
+  cancel-in-progress: true
+
+on:
+  pull_request:
+    branches:
+      - release
+    types:
+      # Default types that triggers a workflow:
+      # - https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request
+      - opened
+      - synchronize
+      - reopened
+      # Additional types that we want to handle:
+      - closed
+
+jobs:
+  notify:
+    runs-on: [ ubuntu-latest ]
+
+    steps:
+      - uses: neondatabase/dev-actions/release-pr-notify@main
+        with:
+          slack-token: ${{ secrets.SLACK_BOT_TOKEN }}
+          slack-channel-id: ${{ vars.SLACK_UPCOMING_RELEASE_CHANNEL_ID || 'C05QQ9J1BRC' }} # if not set, then `#test-release-notifications`
+          github-token: ${{ secrets.GITHUB_TOKEN }}
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -2,16 +2,19 @@ name: Create Release Branch

 on:
  schedule:
-    - cron: '0 10 * * 2'
+    - cron: '0 7 * * 2'
  workflow_dispatch:

 jobs:
  create_release_branch:
-    runs-on: [ubuntu-latest]
+    runs-on: [ ubuntu-latest ]
+
+    permissions:
+      contents: write # for `git push`

    steps:
    - name: Check out code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
      with:
        ref: main

@@ -26,9 +29,16 @@ jobs:
      run: git push origin releases/${{ steps.date.outputs.date }}

    - name: Create pull request into release
-      uses: thomaseizinger/create-pull-request@e3972219c86a56550fb70708d96800d8e24ba862 # 1.3.0
-      with:
-        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        head: releases/${{ steps.date.outputs.date }}
-        base: release
-        title: Release ${{ steps.date.outputs.date }}
+      env:
+        GH_TOKEN: ${{ secrets.CI_ACCESS_TOKEN }}
+      run: |
+        cat << EOF > body.md
+          ## Release ${{ steps.date.outputs.date }}
+
+          **Please merge this PR using 'Create a merge commit'!**
+        EOF
+
+        gh pr create --title "Release ${{ steps.date.outputs.date }}" \
+                     --body-file "body.md" \
+                     --head "releases/${{ steps.date.outputs.date }}" \
+                     --base "release"
--- a/.gitmodules
+++ b/.gitmodules
@@ -6,3 +6,7 @@
 	path = vendor/postgres-v15
 	url = https://github.com/neondatabase/postgres.git
 	branch = REL_15_STABLE_neon
+[submodule "vendor/postgres-v16"]
+	path = vendor/postgres-v16
+	url = https://github.com/neondatabase/postgres.git
+	branch = REL_16_STABLE_neon
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -27,3 +27,28 @@ your patch's fault. Help to fix the root cause if something else has
 broken the CI, before pushing.

 *Happy Hacking!*
+
+# How to run a CI pipeline on Pull Requests from external contributors
+_An instruction for maintainers_
+
+## TL;DR:
+- Review the PR
+- If and only if it looks **safe** (i.e. it doesn't contain any malicious code which could expose secrets or harm the CI), then:
+    - Press the "Approve and run" button in GitHub UI
+    - Add the `approved-for-ci-run` label to the PR
+
+Repeat all steps after any change to the PR.
+- When the changes are ready to get merged — merge the original PR (not the internal one)
+
+## Longer version:
+
+GitHub Actions triggered by the `pull_request` event don't share repository secrets with the forks (for security reasons).
+So, passing the CI pipeline on Pull Requests from external contributors is impossible.
+
+We're using the following approach to make it work:
+- After the review, assign the `approved-for-ci-run` label to the PR if changes look safe
+- A GitHub Action will create an internal branch and a new PR with the same changes (for example, for a PR `#1234`, it'll be a branch `ci-run/pr-1234`)
+- Because the PR is created from the internal branch, it is able to access repository secrets (that's why it's crucial to make sure that the PR doesn't contain any malicious code that could expose our secrets or intentionally harm the CI)
+- The label gets removed automatically, so to run CI again with new changes, the label should be added again (after the review)
+
+For details see [`approved-for-ci-run.yml`](.github/workflows/approved-for-ci-run.yml)
--- a/Cargo.lock
+++ b/Cargo.lock
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,4 +1,5 @@
 [workspace]
+resolver = "2"
 members = [
    "compute_tools",
    "control_plane",
@@ -7,6 +8,7 @@ members = [
    "proxy",
    "safekeeper",
    "storage_broker",
+    "s3_scrubber",
    "workspace_hack",
    "trace",
    "libs/compute_api",
@@ -37,11 +39,11 @@ async-compression = { version = "0.4.0", features = ["tokio", "gzip"] }
 flate2 = "1.0.26"
 async-stream = "0.3"
 async-trait = "0.1"
-aws-config = { version = "0.55", default-features = false, features=["rustls"] }
-aws-sdk-s3 = "0.27"
-aws-smithy-http = "0.55"
-aws-credential-types = "0.55"
-aws-types = "0.55"
+aws-config = { version = "0.56", default-features = false, features=["rustls"] }
+aws-sdk-s3 = "0.29"
+aws-smithy-http = "0.56"
+aws-credential-types = "0.56"
+aws-types = "0.56"
 axum = { version = "0.6.20", features = ["ws"] }
 base64 = "0.13.0"
 bincode = "1.3"
@@ -76,7 +78,7 @@ hostname = "0.3.1"
 humantime = "2.1"
 humantime-serde = "1.1.1"
 hyper = "0.14"
-hyper-tungstenite = "0.9"
+hyper-tungstenite = "0.11"
 inotify = "0.10.2"
 itertools = "0.10"
 jsonwebtoken = "8"
@@ -105,12 +107,12 @@ reqwest-middleware = "0.2.0"
 reqwest-retry = "0.2.2"
 routerify = "3"
 rpds = "0.13"
-rustls = "0.20"
+rustls = "0.21"
 rustls-pemfile = "1"
 rustls-split = "0.3"
 scopeguard = "1.1"
 sysinfo = "0.29.2"
-sentry = { version = "0.30", default-features = false, features = ["backtrace", "contexts", "panic", "rustls", "reqwest" ] }
+sentry = { version = "0.31", default-features = false, features = ["backtrace", "contexts", "panic", "rustls", "reqwest" ] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1"
 serde_with = "2.0"
@@ -125,11 +127,11 @@ sync_wrapper = "0.1.2"
 tar = "0.4"
 test-context = "0.1"
 thiserror = "1.0"
-tls-listener = { version = "0.6", features = ["rustls", "hyper-h1"] }
+tls-listener = { version = "0.7", features = ["rustls", "hyper-h1"] }
 tokio = { version = "1.17", features = ["macros"] }
 tokio-io-timeout = "1.2.0"
-tokio-postgres-rustls = "0.9.0"
-tokio-rustls = "0.23"
+tokio-postgres-rustls = "0.10.0"
+tokio-rustls = "0.24"
 tokio-stream = "0.1"
 tokio-tar = "0.3"
 tokio-util = { version = "0.7", features = ["io"] }
@@ -143,7 +145,7 @@ tracing-subscriber = { version = "0.3", default_features = false, features = ["s
 url = "2.2"
 uuid = { version = "1.2", features = ["v4", "serde"] }
 walkdir = "2.3.2"
-webpki-roots = "0.23"
+webpki-roots = "0.25"
 x509-parser = "0.15"

 ## TODO replace this with tracing
@@ -182,8 +184,8 @@ workspace_hack = { version = "0.1", path = "./workspace_hack/" }

 ## Build dependencies
 criterion = "0.5.1"
-rcgen = "0.10"
-rstest = "0.17"
+rcgen = "0.11"
+rstest = "0.18"
 tempfile = "3.4"
 tonic-build = "0.9"

--- a/4
+++ b/4
@@ -12,6 +12,7 @@ WORKDIR /home/nonroot

 COPY --chown=nonroot vendor/postgres-v14 vendor/postgres-v14
 COPY --chown=nonroot vendor/postgres-v15 vendor/postgres-v15
+COPY --chown=nonroot vendor/postgres-v16 vendor/postgres-v16
 COPY --chown=nonroot pgxn pgxn
 COPY --chown=nonroot Makefile Makefile
 COPY --chown=nonroot scripts/ninstall.sh scripts/ninstall.sh
@@ -39,6 +40,7 @@ ARG CACHEPOT_BUCKET=neon-github-dev

 COPY --from=pg-build /home/nonroot/pg_install/v14/include/postgresql/server pg_install/v14/include/postgresql/server
 COPY --from=pg-build /home/nonroot/pg_install/v15/include/postgresql/server pg_install/v15/include/postgresql/server
+COPY --from=pg-build /home/nonroot/pg_install/v16/include/postgresql/server pg_install/v16/include/postgresql/server
 COPY --chown=nonroot . .

 # Show build caching stats to check if it was used in the end.
@@ -65,6 +67,7 @@ RUN set -e \
    && apt install -y \
        libreadline-dev \
        libseccomp-dev \
+        libicu67 \
        openssl \
        ca-certificates \
    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* \
@@ -81,6 +84,7 @@ COPY --from=build --chown=neon:neon /home/nonroot/target/release/neon_local

 COPY --from=pg-build /home/nonroot/pg_install/v14 /usr/local/v14/
 COPY --from=pg-build /home/nonroot/pg_install/v15 /usr/local/v15/
+COPY --from=pg-build /home/nonroot/pg_install/v16 /usr/local/v16/
 COPY --from=pg-build /home/nonroot/postgres_install.tar.gz /data/

 # By default, pageserver uses `.neon/` working directory in WORKDIR, so create one and fill it with the dummy config.
--- a/Dockerfile.compute-node
+++ b/Dockerfile.compute-node
@@ -74,8 +74,8 @@ RUN wget https://gitlab.com/Oslandia/SFCGAL/-/archive/v1.3.10/SFCGAL-v1.3.10.tar

 ENV PATH "/usr/local/pgsql/bin:$PATH"

-RUN wget https://download.osgeo.org/postgis/source/postgis-3.3.2.tar.gz -O postgis.tar.gz && \
-    echo "9a2a219da005a1730a39d1959a1c7cec619b1efb009b65be80ffc25bad299068 postgis.tar.gz" | sha256sum --check && \
+RUN wget https://download.osgeo.org/postgis/source/postgis-3.3.3.tar.gz -O postgis.tar.gz && \
+    echo "74eb356e3f85f14233791013360881b6748f78081cc688ff9d6f0f673a762d13 postgis.tar.gz" | sha256sum --check && \
    mkdir postgis-src && cd postgis-src && tar xvzf ../postgis.tar.gz --strip-components=1 -C . && \
    find /usr/local/pgsql -type f | sed 's|^/usr/local/pgsql/||' > /before.txt &&\
    ./autogen.sh && \
@@ -124,8 +124,21 @@ COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/
 RUN apt update && \
    apt install -y ninja-build python3-dev libncurses5 binutils clang

-RUN wget https://github.com/plv8/plv8/archive/refs/tags/v3.1.5.tar.gz -O plv8.tar.gz && \
-    echo "1e108d5df639e4c189e1c5bdfa2432a521c126ca89e7e5a969d46899ca7bf106 plv8.tar.gz" | sha256sum --check && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        export PLV8_VERSION=3.1.5 \
+        export PLV8_CHECKSUM=1e108d5df639e4c189e1c5bdfa2432a521c126ca89e7e5a969d46899ca7bf106 \
+        ;; \
+      "v16") \
+        export PLV8_VERSION=3.1.8 \
+        export PLV8_CHECKSUM=92b10c7db39afdae97ff748c9ec54713826af222c459084ad002571b79eb3f49 \
+        ;; \
+      *) \
+        echo "Export the valid PG_VERSION variable" && exit 1 \
+        ;; \
+    esac && \
+    wget https://github.com/plv8/plv8/archive/refs/tags/v${PLV8_VERSION}.tar.gz -O plv8.tar.gz && \
+    echo "${PLV8_CHECKSUM} plv8.tar.gz" | sha256sum --check && \
    mkdir plv8-src && cd plv8-src && tar xvzf ../plv8.tar.gz --strip-components=1 -C . && \
    export PATH="/usr/local/pgsql/bin:$PATH" && \
    make DOCKER=1 -j $(getconf _NPROCESSORS_ONLN) install && \
@@ -172,8 +185,8 @@ RUN wget https://github.com/uber/h3/archive/refs/tags/v4.1.0.tar.gz -O h3.tar.gz
    cp -R /h3/usr / && \
    rm -rf build

-RUN wget https://github.com/zachasme/h3-pg/archive/refs/tags/v4.1.2.tar.gz -O h3-pg.tar.gz && \
-    echo "c135aa45999b2ad1326d2537c1cadef96d52660838e4ca371706c08fdea1a956 h3-pg.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/zachasme/h3-pg/archive/refs/tags/v4.1.3.tar.gz -O h3-pg.tar.gz && \
+    echo "5c17f09a820859ffe949f847bebf1be98511fb8f1bd86f94932512c00479e324 h3-pg.tar.gz" | sha256sum --check && \
    mkdir h3-pg-src && cd h3-pg-src && tar xvzf ../h3-pg.tar.gz --strip-components=1 -C . && \
    export PATH="/usr/local/pgsql/bin:$PATH" && \
    make -j $(getconf _NPROCESSORS_ONLN) && \
@@ -243,8 +256,8 @@ RUN wget https://github.com/michelp/pgjwt/archive/9742dab1b2f297ad3811120db7b214
 FROM build-deps AS hypopg-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

-RUN wget https://github.com/HypoPG/hypopg/archive/refs/tags/1.3.1.tar.gz -O hypopg.tar.gz && \
-    echo "e7f01ee0259dc1713f318a108f987663d60f3041948c2ada57a94b469565ca8e hypopg.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/HypoPG/hypopg/archive/refs/tags/1.4.0.tar.gz -O hypopg.tar.gz && \
+    echo "0821011743083226fc9b813c1f2ef5897a91901b57b6bea85a78e466187c6819 hypopg.tar.gz" | sha256sum --check && \
    mkdir hypopg-src && cd hypopg-src && tar xvzf ../hypopg.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
    make -j $(getconf _NPROCESSORS_ONLN) install PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
@@ -307,8 +320,8 @@ RUN wget https://github.com/theory/pgtap/archive/refs/tags/v1.2.0.tar.gz -O pgta
 FROM build-deps AS ip4r-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

-RUN wget https://github.com/RhodiumToad/ip4r/archive/refs/tags/2.4.1.tar.gz -O ip4r.tar.gz && \
-    echo "78b9f0c1ae45c22182768fe892a32d533c82281035e10914111400bf6301c726 ip4r.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/RhodiumToad/ip4r/archive/refs/tags/2.4.2.tar.gz -O ip4r.tar.gz && \
+    echo "0f7b1f159974f49a47842a8ab6751aecca1ed1142b6d5e38d81b064b2ead1b4b ip4r.tar.gz" | sha256sum --check && \
    mkdir ip4r-src && cd ip4r-src && tar xvzf ../ip4r.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
    make -j $(getconf _NPROCESSORS_ONLN) install PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
@@ -323,8 +336,8 @@ RUN wget https://github.com/RhodiumToad/ip4r/archive/refs/tags/2.4.1.tar.gz -O i
 FROM build-deps AS prefix-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

-RUN wget https://github.com/dimitri/prefix/archive/refs/tags/v1.2.9.tar.gz -O prefix.tar.gz && \
-    echo "38d30a08d0241a8bbb8e1eb8f0152b385051665a8e621c8899e7c5068f8b511e prefix.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/dimitri/prefix/archive/refs/tags/v1.2.10.tar.gz -O prefix.tar.gz && \
+    echo "4342f251432a5f6fb05b8597139d3ccde8dcf87e8ca1498e7ee931ca057a8575 prefix.tar.gz" | sha256sum --check && \
    mkdir prefix-src && cd prefix-src && tar xvzf ../prefix.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
    make -j $(getconf _NPROCESSORS_ONLN) install PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
@@ -339,8 +352,8 @@ RUN wget https://github.com/dimitri/prefix/archive/refs/tags/v1.2.9.tar.gz -O pr
 FROM build-deps AS hll-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

-RUN wget https://github.com/citusdata/postgresql-hll/archive/refs/tags/v2.17.tar.gz -O hll.tar.gz && \
-    echo "9a18288e884f197196b0d29b9f178ba595b0dfc21fbf7a8699380e77fa04c1e9 hll.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/citusdata/postgresql-hll/archive/refs/tags/v2.18.tar.gz -O hll.tar.gz && \
+    echo "e2f55a6f4c4ab95ee4f1b4a2b73280258c5136b161fe9d059559556079694f0e hll.tar.gz" | sha256sum --check && \
    mkdir hll-src && cd hll-src && tar xvzf ../hll.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
    make -j $(getconf _NPROCESSORS_ONLN) install PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
@@ -355,8 +368,8 @@ RUN wget https://github.com/citusdata/postgresql-hll/archive/refs/tags/v2.17.tar
 FROM build-deps AS plpgsql-check-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

-RUN wget https://github.com/okbob/plpgsql_check/archive/refs/tags/v2.3.2.tar.gz -O plpgsql_check.tar.gz && \
-    echo "9d81167c4bbeb74eebf7d60147b21961506161addc2aee537f95ad8efeae427b plpgsql_check.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/okbob/plpgsql_check/archive/refs/tags/v2.4.0.tar.gz -O plpgsql_check.tar.gz && \
+    echo "9ba58387a279b35a3bfa39ee611e5684e6cddb2ba046ddb2c5190b3bd2ca254a plpgsql_check.tar.gz" | sha256sum --check && \
    mkdir plpgsql_check-src && cd plpgsql_check-src && tar xvzf ../plpgsql_check.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) PG_CONFIG=/usr/local/pgsql/bin/pg_config USE_PGXS=1 && \
    make -j $(getconf _NPROCESSORS_ONLN) install PG_CONFIG=/usr/local/pgsql/bin/pg_config USE_PGXS=1 && \
@@ -371,12 +384,21 @@ RUN wget https://github.com/okbob/plpgsql_check/archive/refs/tags/v2.3.2.tar.gz
 FROM build-deps AS timescaledb-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

+ARG PG_VERSION
 ENV PATH "/usr/local/pgsql/bin:$PATH"

-RUN apt-get update && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        export TIMESCALEDB_VERSION=2.10.1 \
+        export TIMESCALEDB_CHECKSUM=6fca72a6ed0f6d32d2b3523951ede73dc5f9b0077b38450a029a5f411fdb8c73 \
+        ;; \
+      *) \
+        echo "TimescaleDB not supported on this PostgreSQL version. See https://github.com/timescale/timescaledb/issues/5752" && exit 0;; \
+    esac && \
+    apt-get update && \
    apt-get install -y cmake && \
-    wget https://github.com/timescale/timescaledb/archive/refs/tags/2.10.1.tar.gz -O timescaledb.tar.gz && \
-    echo "6fca72a6ed0f6d32d2b3523951ede73dc5f9b0077b38450a029a5f411fdb8c73 timescaledb.tar.gz" | sha256sum --check && \
+    wget https://github.com/timescale/timescaledb/archive/refs/tags/${TIMESCALEDB_VERSION}.tar.gz -O timescaledb.tar.gz && \
+    echo "${TIMESCALEDB_CHECKSUM} timescaledb.tar.gz" | sha256sum --check && \
    mkdir timescaledb-src && cd timescaledb-src && tar xvzf ../timescaledb.tar.gz --strip-components=1 -C . && \
    ./bootstrap -DSEND_TELEMETRY_DEFAULT:BOOL=OFF -DUSE_TELEMETRY:BOOL=OFF -DAPACHE_ONLY:BOOL=ON -DCMAKE_BUILD_TYPE=Release && \
    cd build && \
@@ -405,6 +427,10 @@ RUN case "${PG_VERSION}" in \
        export PG_HINT_PLAN_VERSION=15_1_5_0 \
        export PG_HINT_PLAN_CHECKSUM=564cbbf4820973ffece63fbf76e3c0af62c4ab23543142c7caaa682bc48918be \
        ;; \
+      "v16") \
+        export PG_HINT_PLAN_VERSION=16_1_6_0 \
+        export PG_HINT_PLAN_CHECKSUM=fc85a9212e7d2819d4ae4ac75817481101833c3cfa9f0fe1f980984e12347d00 \
+        ;; \
      *) \
        echo "Export the valid PG_HINT_PLAN_VERSION variable" && exit 1 \
        ;; \
@@ -452,8 +478,8 @@ FROM build-deps AS pg-cron-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

 ENV PATH "/usr/local/pgsql/bin/:$PATH"
-RUN wget https://github.com/citusdata/pg_cron/archive/refs/tags/v1.5.2.tar.gz -O pg_cron.tar.gz && \
-    echo "6f7f0980c03f1e2a6a747060e67bf4a303ca2a50e941e2c19daeed2b44dec744 pg_cron.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/citusdata/pg_cron/archive/refs/tags/v1.6.0.tar.gz -O pg_cron.tar.gz && \
+    echo "383a627867d730222c272bfd25cd5e151c578d73f696d32910c7db8c665cc7db pg_cron.tar.gz" | sha256sum --check && \
    mkdir pg_cron-src && cd pg_cron-src && tar xvzf ../pg_cron.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) && \
    make -j $(getconf _NPROCESSORS_ONLN) install && \
@@ -479,8 +505,8 @@ RUN apt-get update && \
        libfreetype6-dev

 ENV PATH "/usr/local/pgsql/bin/:/usr/local/pgsql/:$PATH"
-RUN wget https://github.com/rdkit/rdkit/archive/refs/tags/Release_2023_03_1.tar.gz -O rdkit.tar.gz && \
-    echo "db346afbd0ba52c843926a2a62f8a38c7b774ffab37eaf382d789a824f21996c rdkit.tar.gz" | sha256sum --check && \
+RUN wget https://github.com/rdkit/rdkit/archive/refs/tags/Release_2023_03_3.tar.gz -O rdkit.tar.gz && \
+    echo "bdbf9a2e6988526bfeb8c56ce3cdfe2998d60ac289078e2215374288185e8c8d rdkit.tar.gz" | sha256sum --check && \
    mkdir rdkit-src && cd rdkit-src && tar xvzf ../rdkit.tar.gz --strip-components=1 -C . && \
    cmake \
        -D RDK_BUILD_CAIRO_SUPPORT=OFF \
@@ -551,12 +577,19 @@ FROM build-deps AS pg-embedding-pg-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/

 ENV PATH "/usr/local/pgsql/bin/:$PATH"
-RUN wget https://github.com/neondatabase/pg_embedding/archive/refs/tags/0.3.5.tar.gz -O pg_embedding.tar.gz && \
-    echo "0e95b27b8b6196e2cf0a0c9ec143fe2219b82e54c5bb4ee064e76398cbe69ae9 pg_embedding.tar.gz" | sha256sum --check && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        export PG_EMBEDDING_VERSION=0.3.5 \
+        export PG_EMBEDDING_CHECKSUM=0e95b27b8b6196e2cf0a0c9ec143fe2219b82e54c5bb4ee064e76398cbe69ae9 \
+        ;; \
+      *) \
+        echo "pg_embedding not supported on this PostgreSQL version. Use pgvector instead." && exit 0;; \
+    esac && \
+    wget https://github.com/neondatabase/pg_embedding/archive/refs/tags/${PG_EMBEDDING_VERSION}.tar.gz -O pg_embedding.tar.gz && \
+    echo "${PG_EMBEDDING_CHECKSUM} pg_embedding.tar.gz" | sha256sum --check && \
    mkdir pg_embedding-src && cd pg_embedding-src && tar xvzf ../pg_embedding.tar.gz --strip-components=1 -C . && \
    make -j $(getconf _NPROCESSORS_ONLN) && \
-    make -j $(getconf _NPROCESSORS_ONLN) install && \
-    echo 'trusted = true' >> /usr/local/pgsql/share/extension/embedding.control
+    make -j $(getconf _NPROCESSORS_ONLN) install

 #########################################################################################
 #
@@ -584,6 +617,10 @@ RUN wget https://gitlab.com/dalibo/postgresql_anonymizer/-/archive/1.1.0/postgre
 # Layer "rust extensions"
 # This layer is used to build `pgx` deps
 #
+# FIXME: This needs to be updated to latest version of 'pgrx' (it was renamed from
+# 'pgx' to 'pgrx') for PostgreSQL 16. And that in turn requires bumping the pgx
+# dependency on all the rust extension that depend on it, too.
+#
 #########################################################################################
 FROM build-deps AS rust-extensions-build
 COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/
@@ -598,7 +635,17 @@ USER nonroot
 WORKDIR /home/nonroot
 ARG PG_VERSION

-RUN curl -sSO https://static.rust-lang.org/rustup/dist/$(uname -m)-unknown-linux-gnu/rustup-init && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        ;; \
+      "v16") \
+        echo "TODO: Not yet supported for PostgreSQL 16. Need to update pgrx dependencies" && exit 0 \
+	;; \
+      *) \
+        echo "unexpected PostgreSQL version ${PG_VERSION}" && exit 1 \
+        ;; \
+    esac && \
+    curl -sSO https://static.rust-lang.org/rustup/dist/$(uname -m)-unknown-linux-gnu/rustup-init && \
    chmod +x rustup-init && \
    ./rustup-init -y --no-modify-path --profile minimal --default-toolchain stable && \
    rm rustup-init && \
@@ -615,10 +662,21 @@ USER root
 #########################################################################################

 FROM rust-extensions-build AS pg-jsonschema-pg-build
+ARG PG_VERSION

 # caeab60d70b2fd3ae421ec66466a3abbb37b7ee6 made on 06/03/2023
 # there is no release tag yet, but we need it due to the superuser fix in the control file, switch to git tag after release >= 0.1.5
-RUN wget https://github.com/supabase/pg_jsonschema/archive/caeab60d70b2fd3ae421ec66466a3abbb37b7ee6.tar.gz -O pg_jsonschema.tar.gz && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        ;; \
+      "v16") \
+        echo "TODO: Not yet supported for PostgreSQL 16. Need to update pgrx dependencies" && exit 0 \
+	;; \
+      *) \
+        echo "unexpected PostgreSQL version \"${PG_VERSION}\"" && exit 1 \
+        ;; \
+    esac && \
+    wget https://github.com/supabase/pg_jsonschema/archive/caeab60d70b2fd3ae421ec66466a3abbb37b7ee6.tar.gz -O pg_jsonschema.tar.gz && \
    echo "54129ce2e7ee7a585648dbb4cef6d73f795d94fe72f248ac01119992518469a4 pg_jsonschema.tar.gz" | sha256sum --check && \
    mkdir pg_jsonschema-src && cd pg_jsonschema-src && tar xvzf ../pg_jsonschema.tar.gz --strip-components=1 -C . && \
    sed -i 's/pgx = "0.7.1"/pgx = { version = "0.7.3", features = [ "unsafe-postgres" ] }/g' Cargo.toml && \
@@ -633,12 +691,23 @@ RUN wget https://github.com/supabase/pg_jsonschema/archive/caeab60d70b2fd3ae421e
 #########################################################################################

 FROM rust-extensions-build AS pg-graphql-pg-build
+ARG PG_VERSION

 # b4988843647450a153439be367168ed09971af85 made on 22/02/2023 (from remove-pgx-contrib-spiext branch)
 # Currently pgx version bump to >= 0.7.2  causes "call to unsafe function" compliation errors in
 # pgx-contrib-spiext. There is a branch that removes that dependency, so use it. It is on the
 # same 1.1 version we've used before.
-RUN wget https://github.com/yrashk/pg_graphql/archive/b4988843647450a153439be367168ed09971af85.tar.gz -O pg_graphql.tar.gz && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        ;; \
+      "v16") \
+        echo "TODO: Not yet supported for PostgreSQL 16. Need to update pgrx dependencies" && exit 0 \
+	;; \
+      *) \
+        echo "unexpected PostgreSQL version" && exit 1 \
+        ;; \
+    esac && \
+    wget https://github.com/yrashk/pg_graphql/archive/b4988843647450a153439be367168ed09971af85.tar.gz -O pg_graphql.tar.gz && \
    echo "0c7b0e746441b2ec24187d0e03555faf935c2159e2839bddd14df6dafbc8c9bd pg_graphql.tar.gz" | sha256sum --check && \
    mkdir pg_graphql-src && cd pg_graphql-src && tar xvzf ../pg_graphql.tar.gz --strip-components=1 -C . && \
    sed -i 's/pgx = "~0.7.1"/pgx = { version = "0.7.3", features = [ "unsafe-postgres" ] }/g' Cargo.toml && \
@@ -656,9 +725,20 @@ RUN wget https://github.com/yrashk/pg_graphql/archive/b4988843647450a153439be367
 #########################################################################################

 FROM rust-extensions-build AS pg-tiktoken-pg-build
+ARG PG_VERSION

 # 801f84f08c6881c8aa30f405fafbf00eec386a72 made on 10/03/2023
-RUN wget https://github.com/kelvich/pg_tiktoken/archive/801f84f08c6881c8aa30f405fafbf00eec386a72.tar.gz -O pg_tiktoken.tar.gz && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        ;; \
+      "v16") \
+        echo "TODO: Not yet supported for PostgreSQL 16. Need to update pgrx dependencies" && exit 0 \
+	;; \
+      *) \
+        echo "unexpected PostgreSQL version" && exit 1 \
+        ;; \
+    esac && \
+    wget https://github.com/kelvich/pg_tiktoken/archive/801f84f08c6881c8aa30f405fafbf00eec386a72.tar.gz -O pg_tiktoken.tar.gz && \
    echo "52f60ac800993a49aa8c609961842b611b6b1949717b69ce2ec9117117e16e4a pg_tiktoken.tar.gz" | sha256sum --check && \
    mkdir pg_tiktoken-src && cd pg_tiktoken-src && tar xvzf ../pg_tiktoken.tar.gz --strip-components=1 -C . && \
    cargo pgx install --release && \
@@ -672,8 +752,19 @@ RUN wget https://github.com/kelvich/pg_tiktoken/archive/801f84f08c6881c8aa30f405
 #########################################################################################

 FROM rust-extensions-build AS pg-pgx-ulid-build
+ARG PG_VERSION

-RUN wget https://github.com/pksunkara/pgx_ulid/archive/refs/tags/v0.1.0.tar.gz -O pgx_ulid.tar.gz && \
+RUN case "${PG_VERSION}" in \
+      "v14" | "v15") \
+        ;; \
+      "v16") \
+        echo "TODO: Not yet supported for PostgreSQL 16. Need to update pgrx dependencies" && exit 0 \
+	;; \
+      *) \
+        echo "unexpected PostgreSQL version" && exit 1 \
+        ;; \
+    esac && \
+    wget https://github.com/pksunkara/pgx_ulid/archive/refs/tags/v0.1.0.tar.gz -O pgx_ulid.tar.gz && \
    echo "908b7358e6f846e87db508ae5349fb56a88ee6305519074b12f3d5b0ff09f791 pgx_ulid.tar.gz" | sha256sum --check && \
    mkdir pgx_ulid-src && cd pgx_ulid-src && tar xvzf ../pgx_ulid.tar.gz --strip-components=1 -C . && \
    sed -i 's/pgx        = "=0.7.3"/pgx = { version = "0.7.3", features = [ "unsafe-postgres" ] }/g' Cargo.toml && \
@@ -726,6 +817,20 @@ RUN make -j $(getconf _NPROCESSORS_ONLN) \
        PG_CONFIG=/usr/local/pgsql/bin/pg_config \
        -C pgxn/neon_utils \
        -s install && \
+    make -j $(getconf _NPROCESSORS_ONLN) \
+        PG_CONFIG=/usr/local/pgsql/bin/pg_config \
+        -C pgxn/neon_rmgr \
+        -s install && \
+    case "${PG_VERSION}" in \
+        "v14" | "v15") \
+        ;; \
+        "v16") \
+            echo "Skipping HNSW for PostgreSQL 16" && exit 0 \
+        ;; \
+        *) \
+            echo "unexpected PostgreSQL version" && exit 1 \
+        ;; \
+        esac && \
    make -j $(getconf _NPROCESSORS_ONLN) \
        PG_CONFIG=/usr/local/pgsql/bin/pg_config \
        -C pgxn/hnsw \
--- a/41
+++ b/41
@@ -29,6 +29,7 @@ else ifeq ($(UNAME_S),Darwin)
 	# It can be configured with OPENSSL_PREFIX variable
 	OPENSSL_PREFIX ?= $(shell brew --prefix openssl@3)
 	PG_CONFIGURE_OPTS += --with-includes=$(OPENSSL_PREFIX)/include --with-libraries=$(OPENSSL_PREFIX)/lib
+	PG_CONFIGURE_OPTS += PKG_CONFIG_PATH=$(shell brew --prefix icu4c)/lib/pkgconfig
 	# macOS already has bison and flex in the system, but they are old and result in postgres-v14 target failure
 	# brew formulae are keg-only and not symlinked into HOMEBREW_PREFIX, force their usage
 	EXTRA_PATH_OVERRIDES += $(shell brew --prefix bison)/bin/:$(shell brew --prefix flex)/bin/:
@@ -83,6 +84,8 @@ $(POSTGRES_INSTALL_DIR)/build/%/config.status:
 # I'm not sure why it wouldn't work, but this is the only place (apart from
 # the "build-all-versions" entry points) where direct mention of PostgreSQL
 # versions is used.
+.PHONY: postgres-configure-v16
+postgres-configure-v16: $(POSTGRES_INSTALL_DIR)/build/v16/config.status
 .PHONY: postgres-configure-v15
 postgres-configure-v15: $(POSTGRES_INSTALL_DIR)/build/v15/config.status
 .PHONY: postgres-configure-v14
@@ -118,6 +121,10 @@ postgres-clean-%:
 	$(MAKE) -C $(POSTGRES_INSTALL_DIR)/build/$*/contrib/pageinspect clean
 	$(MAKE) -C $(POSTGRES_INSTALL_DIR)/build/$*/src/interfaces/libpq clean

+.PHONY: postgres-check-%
+postgres-check-%: postgres-%
+	$(MAKE) -C $(POSTGRES_INSTALL_DIR)/build/$* MAKELEVEL=0 check
+
 .PHONY: neon-pg-ext-%
 neon-pg-ext-%: postgres-%
 	+@echo "Compiling neon $*"
@@ -130,6 +137,11 @@ neon-pg-ext-%: postgres-%
 	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config CFLAGS='$(PG_CFLAGS) $(COPT)' \
 		-C $(POSTGRES_INSTALL_DIR)/build/neon-walredo-$* \
 		-f $(ROOT_PROJECT_DIR)/pgxn/neon_walredo/Makefile install
+	+@echo "Compiling neon_rmgr $*"
+	mkdir -p $(POSTGRES_INSTALL_DIR)/build/neon-rmgr-$*
+	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config CFLAGS='$(PG_CFLAGS) $(COPT)' \
+		-C $(POSTGRES_INSTALL_DIR)/build/neon-rmgr-$* \
+		-f $(ROOT_PROJECT_DIR)/pgxn/neon_rmgr/Makefile install
 	+@echo "Compiling neon_test_utils $*"
 	mkdir -p $(POSTGRES_INSTALL_DIR)/build/neon-test-utils-$*
 	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config CFLAGS='$(PG_CFLAGS) $(COPT)' \
@@ -140,11 +152,6 @@ neon-pg-ext-%: postgres-%
 	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config CFLAGS='$(PG_CFLAGS) $(COPT)' \
 		-C $(POSTGRES_INSTALL_DIR)/build/neon-utils-$* \
 		-f $(ROOT_PROJECT_DIR)/pgxn/neon_utils/Makefile install
-	+@echo "Compiling hnsw $*"
-	mkdir -p $(POSTGRES_INSTALL_DIR)/build/hnsw-$*
-	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config CFLAGS='$(PG_CFLAGS) $(COPT)' \
-		-C $(POSTGRES_INSTALL_DIR)/build/hnsw-$* \
-		-f $(ROOT_PROJECT_DIR)/pgxn/hnsw/Makefile install

 .PHONY: neon-pg-ext-clean-%
 neon-pg-ext-clean-%:
@@ -160,35 +167,43 @@ neon-pg-ext-clean-%:
 	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config \
 	-C $(POSTGRES_INSTALL_DIR)/build/neon-utils-$* \
 	-f $(ROOT_PROJECT_DIR)/pgxn/neon_utils/Makefile clean
-	$(MAKE) PG_CONFIG=$(POSTGRES_INSTALL_DIR)/$*/bin/pg_config \
-	-C $(POSTGRES_INSTALL_DIR)/build/hnsw-$* \
-	-f $(ROOT_PROJECT_DIR)/pgxn/hnsw/Makefile clean

 .PHONY: neon-pg-ext
 neon-pg-ext: \
 	neon-pg-ext-v14 \
-	neon-pg-ext-v15
+	neon-pg-ext-v15 \
+	neon-pg-ext-v16

 .PHONY: neon-pg-ext-clean
 neon-pg-ext-clean: \
 	neon-pg-ext-clean-v14 \
-	neon-pg-ext-clean-v15
+	neon-pg-ext-clean-v15 \
+	neon-pg-ext-clean-v16

 # shorthand to build all Postgres versions
 .PHONY: postgres
 postgres: \
 	postgres-v14 \
-	postgres-v15
+	postgres-v15 \
+	postgres-v16

 .PHONY: postgres-headers
 postgres-headers: \
 	postgres-headers-v14 \
-	postgres-headers-v15
+	postgres-headers-v15 \
+	postgres-headers-v16

 .PHONY: postgres-clean
 postgres-clean: \
 	postgres-clean-v14 \
-	postgres-clean-v15
+	postgres-clean-v15 \
+	postgres-clean-v16
+
+.PHONY: postgres-check
+postgres-check: \
+	postgres-check-v14 \
+	postgres-check-v15 \
+	postgres-check-v16

 # This doesn't remove the effects of 'configure'.
 .PHONY: clean
--- a/README.md
+++ b/README.md
@@ -29,18 +29,18 @@ See developer documentation in [SUMMARY.md](/docs/SUMMARY.md) for more informati
 ```bash
 apt install build-essential libtool libreadline-dev zlib1g-dev flex bison libseccomp-dev \
 libssl-dev clang pkg-config libpq-dev cmake postgresql-client protobuf-compiler \
-libcurl4-openssl-dev openssl python-poetry
+libcurl4-openssl-dev openssl python-poetry lsof libicu-dev
 ```
 * On Fedora, these packages are needed:
 ```bash
 dnf install flex bison readline-devel zlib-devel openssl-devel \
  libseccomp-devel perl clang cmake postgresql postgresql-contrib protobuf-compiler \
-  protobuf-devel libcurl-devel openssl poetry
+  protobuf-devel libcurl-devel openssl poetry lsof libicu-devel
 ```
 * On Arch based systems, these packages are needed:
 ```bash
 pacman -S base-devel readline zlib libseccomp openssl clang \
-postgresql-libs cmake postgresql protobuf curl
+postgresql-libs cmake postgresql protobuf curl lsof
 ```

 Building Neon requires 3.15+ version of `protoc` (protobuf-compiler). If your distribution provides an older version, you can install a newer version from [here](https://github.com/protocolbuffers/protobuf/releases).
@@ -55,7 +55,7 @@ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
 1. Install XCode and dependencies
 ```
 xcode-select --install
-brew install protobuf openssl flex bison
+brew install protobuf openssl flex bison icu4c pkg-config

 # add openssl to PATH, required for ed25519 keys generation in neon_local
 echo 'export PATH="$(brew --prefix openssl)/bin:$PATH"' >> ~/.zshrc
--- a/clippy.toml
+++ b/clippy.toml
@@ -0,0 +1,5 @@
+disallowed-methods = [
+    "tokio::task::block_in_place",
+    # Allow this for now, to deny it later once we stop using Handle::block_on completely
+    # "tokio::runtime::Handle::block_on",
+]
--- a/compute_tools/src/checker.rs
+++ b/compute_tools/src/checker.rs
@@ -1,12 +1,39 @@
-use anyhow::{anyhow, Result};
+use anyhow::{anyhow, Ok, Result};
+use postgres::Client;
 use tokio_postgres::NoTls;
-use tracing::{error, instrument};
+use tracing::{error, instrument, warn};

 use crate::compute::ComputeNode;

+/// Create a special service table for availability checks
+/// only if it does not exist already.
+pub fn create_availability_check_data(client: &mut Client) -> Result<()> {
+    let query = "
+        DO $$
+        BEGIN
+            IF NOT EXISTS(
+                SELECT 1
+                FROM pg_catalog.pg_tables
+                WHERE tablename = 'health_check'
+            )
+            THEN
+            CREATE TABLE health_check (
+                id serial primary key,
+                updated_at timestamptz default now()
+            );
+            INSERT INTO health_check VALUES (1, now())
+                ON CONFLICT (id) DO UPDATE
+                 SET updated_at = now();
+            END IF;
+        END
+        $$;";
+    client.execute(query, &[])?;
+
+    Ok(())
+}
+
 /// Update timestamp in a row in a special service table to check
 /// that we can actually write some data in this particular timeline.
-/// Create table if it's missing.
 #[instrument(skip_all)]
 pub async fn check_writability(compute: &ComputeNode) -> Result<()> {
    // Connect to the database.
@@ -24,21 +51,28 @@ pub async fn check_writability(compute: &ComputeNode) -> Result<()> {
    });

    let query = "
-    CREATE TABLE IF NOT EXISTS health_check (
-        id serial primary key,
-        updated_at timestamptz default now()
-    );
    INSERT INTO health_check VALUES (1, now())
        ON CONFLICT (id) DO UPDATE
         SET updated_at = now();";

-    let result = client.simple_query(query).await?;
-
-    if result.len() != 2 {
-        return Err(anyhow::format_err!(
-            "expected 2 query results, but got {}",
-            result.len()
-        ));
+    match client.simple_query(query).await {
+        Result::Ok(result) => {
+            if result.len() != 1 {
+                return Err(anyhow::anyhow!(
+                    "expected 1 query results, but got {}",
+                    result.len()
+                ));
+            }
+        }
+        Err(err) => {
+            if let Some(state) = err.code() {
+                if state == &tokio_postgres::error::SqlState::DISK_FULL {
+                    warn!("Tenant disk is full");
+                    return Ok(());
+                }
+            }
+            return Err(err.into());
+        }
    }

    Ok(())
--- a/compute_tools/src/compute.rs
+++ b/compute_tools/src/compute.rs
@@ -27,6 +27,7 @@ use utils::measured_stream::MeasuredReader;

 use remote_storage::{DownloadError, GenericRemoteStorage, RemotePath};

+use crate::checker::create_availability_check_data;
 use crate::pg_helpers::*;
 use crate::spec::*;
 use crate::sync_sk::{check_if_synced, ping_safekeeper};
@@ -696,6 +697,7 @@ impl ComputeNode {
        handle_role_deletions(spec, self.connstr.as_str(), &mut client)?;
        handle_grants(spec, self.connstr.as_str())?;
        handle_extensions(spec, &mut client)?;
+        create_availability_check_data(&mut client)?;

        // 'Close' connection
        drop(client);
@@ -1078,7 +1080,8 @@ LIMIT 100",

        let mut download_tasks = Vec::new();
        for library in &libs_vec {
-            let (ext_name, ext_path) = remote_extensions.get_ext(library, true)?;
+            let (ext_name, ext_path) =
+                remote_extensions.get_ext(library, true, &self.build_tag, &self.pgversion)?;
            download_tasks.push(self.download_extension(ext_name, ext_path));
        }
        let results = join_all(download_tasks).await;
--- a/compute_tools/src/config.rs
+++ b/compute_tools/src/config.rs
@@ -46,8 +46,6 @@ pub fn write_postgres_conf(
        writeln!(file, "{}", conf)?;
    }

-    write!(file, "{}", &spec.cluster.settings.as_pg_settings())?;
-
    // Add options for connecting to storage
    writeln!(file, "# Neon storage settings")?;
    if let Some(s) = &spec.pageserver_connstring {
--- a/compute_tools/src/extension_server.rs
+++ b/compute_tools/src/extension_server.rs
@@ -74,6 +74,7 @@ More specifically, here is an example ext_index.json
 use anyhow::Context;
 use anyhow::{self, Result};
 use compute_api::spec::RemoteExtSpec;
+use regex::Regex;
 use remote_storage::*;
 use serde_json;
 use std::io::Read;
@@ -106,16 +107,71 @@ fn get_pg_config(argument: &str, pgbin: &str) -> String {

 pub fn get_pg_version(pgbin: &str) -> String {
    // pg_config --version returns a (platform specific) human readable string
-    // such as "PostgreSQL 15.4". We parse this to v14/v15
+    // such as "PostgreSQL 15.4". We parse this to v14/v15/v16 etc.
    let human_version = get_pg_config("--version", pgbin);
-    if human_version.contains("15") {
-        return "v15".to_string();
-    } else if human_version.contains("14") {
-        return "v14".to_string();
+    return parse_pg_version(&human_version).to_string();
+}
+
+fn parse_pg_version(human_version: &str) -> &str {
+    // Normal releases have version strings like "PostgreSQL 15.4". But there
+    // are also pre-release versions like "PostgreSQL 17devel" or "PostgreSQL
+    // 16beta2" or "PostgreSQL 17rc1". And with the --with-extra-version
+    // configure option, you can tack any string to the version number,
+    // e.g. "PostgreSQL 15.4foobar".
+    match Regex::new(r"^PostgreSQL (?<major>\d+).+")
+        .unwrap()
+        .captures(human_version)
+    {
+        Some(captures) if captures.len() == 2 => match &captures["major"] {
+            "14" => return "v14",
+            "15" => return "v15",
+            "16" => return "v16",
+            _ => {}
+        },
+        _ => {}
    }
    panic!("Unsuported postgres version {human_version}");
 }

+#[cfg(test)]
+mod tests {
+    use super::parse_pg_version;
+
+    #[test]
+    fn test_parse_pg_version() {
+        assert_eq!(parse_pg_version("PostgreSQL 15.4"), "v15");
+        assert_eq!(parse_pg_version("PostgreSQL 15.14"), "v15");
+        assert_eq!(
+            parse_pg_version("PostgreSQL 15.4 (Ubuntu 15.4-0ubuntu0.23.04.1)"),
+            "v15"
+        );
+
+        assert_eq!(parse_pg_version("PostgreSQL 14.15"), "v14");
+        assert_eq!(parse_pg_version("PostgreSQL 14.0"), "v14");
+        assert_eq!(
+            parse_pg_version("PostgreSQL 14.9 (Debian 14.9-1.pgdg120+1"),
+            "v14"
+        );
+
+        assert_eq!(parse_pg_version("PostgreSQL 16devel"), "v16");
+        assert_eq!(parse_pg_version("PostgreSQL 16beta1"), "v16");
+        assert_eq!(parse_pg_version("PostgreSQL 16rc2"), "v16");
+        assert_eq!(parse_pg_version("PostgreSQL 16extra"), "v16");
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_parse_pg_unsupported_version() {
+        parse_pg_version("PostgreSQL 13.14");
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_parse_pg_incorrect_version_format() {
+        parse_pg_version("PostgreSQL 14");
+    }
+}
+
 // download the archive for a given extension,
 // unzip it, and place files in the appropriate locations (share/lib)
 pub async fn download_extension(
@@ -180,7 +236,19 @@ pub async fn download_extension(
 // Create extension control files from spec
 pub fn create_control_files(remote_extensions: &RemoteExtSpec, pgbin: &str) {
    let local_sharedir = Path::new(&get_pg_config("--sharedir", pgbin)).join("extension");
-    for ext_data in remote_extensions.extension_data.values() {
+    for (ext_name, ext_data) in remote_extensions.extension_data.iter() {
+        // Check if extension is present in public or custom.
+        // If not, then it is not allowed to be used by this compute.
+        if let Some(public_extensions) = &remote_extensions.public_extensions {
+            if !public_extensions.contains(ext_name) {
+                if let Some(custom_extensions) = &remote_extensions.custom_extensions {
+                    if !custom_extensions.contains(ext_name) {
+                        continue; // skip this extension, it is not allowed
+                    }
+                }
+            }
+        }
+
        for (control_name, control_content) in &ext_data.control_data {
            let control_path = local_sharedir.join(control_name);
            if !control_path.exists() {
--- a/compute_tools/src/http/api.rs
+++ b/compute_tools/src/http/api.rs
@@ -1,4 +1,6 @@
 use std::convert::Infallible;
+use std::net::IpAddr;
+use std::net::Ipv6Addr;
 use std::net::SocketAddr;
 use std::sync::Arc;
 use std::thread;
@@ -169,7 +171,12 @@ async fn routes(req: Request<Body>, compute: &Arc<ComputeNode>) -> Response<Body
                    }
                };

-                remote_extensions.get_ext(&filename, is_library)
+                remote_extensions.get_ext(
+                    &filename,
+                    is_library,
+                    &compute.build_tag,
+                    &compute.pgversion,
+                )
            };

            match ext {
@@ -293,7 +300,9 @@ fn render_json_error(e: &str, status: StatusCode) -> Response<Body> {
 // Main Hyper HTTP server function that runs it and blocks waiting on it forever.
 #[tokio::main]
 async fn serve(port: u16, state: Arc<ComputeNode>) {
-    let addr = SocketAddr::from(([0, 0, 0, 0], port));
+    // this usually binds to both IPv4 and IPv6 on linux
+    // see e.g. https://github.com/rust-lang/rust/pull/34440
+    let addr = SocketAddr::new(IpAddr::from(Ipv6Addr::UNSPECIFIED), port);

    let make_service = make_service_fn(move |_conn| {
        let state = state.clone();
--- a/compute_tools/src/params.rs
+++ b/compute_tools/src/params.rs
@@ -6,4 +6,4 @@ pub const DEFAULT_LOG_LEVEL: &str = "info";
 //   https://www.postgresql.org/docs/15/auth-password.html
 //
 // So it's safe to set md5 here, as `control-plane` anyway uses SCRAM for all roles.
-pub const PG_HBA_ALL_MD5: &str = "host\tall\t\tall\t\t0.0.0.0/0\t\tmd5";
+pub const PG_HBA_ALL_MD5: &str = "host\tall\t\tall\t\tall\t\tmd5";
--- a/control_plane/Cargo.toml
+++ b/control_plane/Cargo.toml
@@ -12,6 +12,8 @@ git-version.workspace = true
 nix.workspace = true
 once_cell.workspace = true
 postgres.workspace = true
+hex.workspace = true
+hyper.workspace = true
 regex.workspace = true
 reqwest = { workspace = true, features = ["blocking", "json"] }
 serde.workspace = true
@@ -20,6 +22,7 @@ serde_with.workspace = true
 tar.workspace = true
 thiserror.workspace = true
 toml.workspace = true
+tokio.workspace = true
 url.workspace = true
 # Note: Do not directly depend on pageserver or safekeeper; use pageserver_api or safekeeper_api
 # instead, so that recompile times are better.
--- a/control_plane/simple.conf
+++ b/control_plane/simple.conf
@@ -1,6 +1,7 @@
 # Minimal neon environment with one safekeeper. This is equivalent to the built-in
 # defaults that you get with no --config
-[pageserver]
+[[pageservers]]
+id=1
 listen_pg_addr = '127.0.0.1:64000'
 listen_http_addr = '127.0.0.1:9898'
 pg_auth_type = 'Trust'
--- a/control_plane/src/attachment_service.rs
+++ b/control_plane/src/attachment_service.rs
@@ -0,0 +1,105 @@
+use crate::{background_process, local_env::LocalEnv};
+use anyhow::anyhow;
+use serde::{Deserialize, Serialize};
+use serde_with::{serde_as, DisplayFromStr};
+use std::{path::PathBuf, process::Child};
+use utils::id::{NodeId, TenantId};
+
+pub struct AttachmentService {
+    env: LocalEnv,
+    listen: String,
+    path: PathBuf,
+}
+
+const COMMAND: &str = "attachment_service";
+
+#[serde_as]
+#[derive(Serialize, Deserialize)]
+pub struct AttachHookRequest {
+    #[serde_as(as = "DisplayFromStr")]
+    pub tenant_id: TenantId,
+    pub pageserver_id: Option<NodeId>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct AttachHookResponse {
+    pub gen: Option<u32>,
+}
+
+impl AttachmentService {
+    pub fn from_env(env: &LocalEnv) -> Self {
+        let path = env.base_data_dir.join("attachments.json");
+
+        // Makes no sense to construct this if pageservers aren't going to use it: assume
+        // pageservers have control plane API set
+        let listen_url = env.control_plane_api.clone().unwrap();
+
+        let listen = format!(
+            "{}:{}",
+            listen_url.host_str().unwrap(),
+            listen_url.port().unwrap()
+        );
+
+        Self {
+            env: env.clone(),
+            path,
+            listen,
+        }
+    }
+
+    fn pid_file(&self) -> PathBuf {
+        self.env.base_data_dir.join("attachment_service.pid")
+    }
+
+    pub fn start(&self) -> anyhow::Result<Child> {
+        let path_str = self.path.to_string_lossy();
+
+        background_process::start_process(
+            COMMAND,
+            &self.env.base_data_dir,
+            &self.env.attachment_service_bin(),
+            ["-l", &self.listen, "-p", &path_str],
+            [],
+            background_process::InitialPidFile::Create(&self.pid_file()),
+            // TODO: a real status check
+            || Ok(true),
+        )
+    }
+
+    pub fn stop(&self, immediate: bool) -> anyhow::Result<()> {
+        background_process::stop_process(immediate, COMMAND, &self.pid_file())
+    }
+
+    /// Call into the attach_hook API, for use before handing out attachments to pageservers
+    pub fn attach_hook(
+        &self,
+        tenant_id: TenantId,
+        pageserver_id: NodeId,
+    ) -> anyhow::Result<Option<u32>> {
+        use hyper::StatusCode;
+
+        let url = self
+            .env
+            .control_plane_api
+            .clone()
+            .unwrap()
+            .join("attach_hook")
+            .unwrap();
+        let client = reqwest::blocking::ClientBuilder::new()
+            .build()
+            .expect("Failed to construct http client");
+
+        let request = AttachHookRequest {
+            tenant_id,
+            pageserver_id: Some(pageserver_id),
+        };
+
+        let response = client.post(url).json(&request).send()?;
+        if response.status() != StatusCode::OK {
+            return Err(anyhow!("Unexpected status {}", response.status()));
+        }
+
+        let response = response.json::<AttachHookResponse>()?;
+        Ok(response.gen)
+    }
+}
--- a/control_plane/src/bin/attachment_service.rs
+++ b/control_plane/src/bin/attachment_service.rs
@@ -0,0 +1,273 @@
+/// The attachment service mimics the aspects of the control plane API
+/// that are required for a pageserver to operate.
+///
+/// This enables running & testing pageservers without a full-blown
+/// deployment of the Neon cloud platform.
+///
+use anyhow::anyhow;
+use clap::Parser;
+use hex::FromHex;
+use hyper::StatusCode;
+use hyper::{Body, Request, Response};
+use serde::{Deserialize, Serialize};
+use std::path::{Path, PathBuf};
+use std::{collections::HashMap, sync::Arc};
+use utils::logging::{self, LogFormat};
+
+use utils::{
+    http::{
+        endpoint::{self},
+        error::ApiError,
+        json::{json_request, json_response},
+        RequestExt, RouterBuilder,
+    },
+    id::{NodeId, TenantId},
+    tcp_listener,
+};
+
+use pageserver_api::control_api::{
+    ReAttachRequest, ReAttachResponse, ReAttachResponseTenant, ValidateRequest, ValidateResponse,
+    ValidateResponseTenant,
+};
+
+use control_plane::attachment_service::{AttachHookRequest, AttachHookResponse};
+
+#[derive(Parser)]
+#[command(author, version, about, long_about = None)]
+#[command(arg_required_else_help(true))]
+struct Cli {
+    /// Host and port to listen on, like `127.0.0.1:1234`
+    #[arg(short, long)]
+    listen: std::net::SocketAddr,
+
+    /// Path to the .json file to store state (will be created if it doesn't exist)
+    #[arg(short, long)]
+    path: PathBuf,
+}
+
+// The persistent state of each Tenant
+#[derive(Serialize, Deserialize, Clone)]
+struct TenantState {
+    // Currently attached pageserver
+    pageserver: Option<NodeId>,
+
+    // Latest generation number: next time we attach, increment this
+    // and use the incremented number when attaching
+    generation: u32,
+}
+
+fn to_hex_map<S, V>(input: &HashMap<TenantId, V>, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: serde::Serializer,
+    V: Clone + Serialize,
+{
+    let transformed = input.iter().map(|(k, v)| (hex::encode(k), v.clone()));
+
+    transformed
+        .collect::<HashMap<String, V>>()
+        .serialize(serializer)
+}
+
+fn from_hex_map<'de, D, V>(deserializer: D) -> Result<HashMap<TenantId, V>, D::Error>
+where
+    D: serde::de::Deserializer<'de>,
+    V: Deserialize<'de>,
+{
+    let hex_map = HashMap::<String, V>::deserialize(deserializer)?;
+    hex_map
+        .into_iter()
+        .map(|(k, v)| {
+            TenantId::from_hex(k)
+                .map(|k| (k, v))
+                .map_err(serde::de::Error::custom)
+        })
+        .collect()
+}
+
+// Top level state available to all HTTP handlers
+#[derive(Serialize, Deserialize)]
+struct PersistentState {
+    #[serde(serialize_with = "to_hex_map", deserialize_with = "from_hex_map")]
+    tenants: HashMap<TenantId, TenantState>,
+
+    #[serde(skip)]
+    path: PathBuf,
+}
+
+impl PersistentState {
+    async fn save(&self) -> anyhow::Result<()> {
+        let bytes = serde_json::to_vec(self)?;
+        tokio::fs::write(&self.path, &bytes).await?;
+
+        Ok(())
+    }
+
+    async fn load(path: &Path) -> anyhow::Result<Self> {
+        let bytes = tokio::fs::read(path).await?;
+        let mut decoded = serde_json::from_slice::<Self>(&bytes)?;
+        decoded.path = path.to_owned();
+        Ok(decoded)
+    }
+
+    async fn load_or_new(path: &Path) -> Self {
+        match Self::load(path).await {
+            Ok(s) => {
+                tracing::info!("Loaded state file at {}", path.display());
+                s
+            }
+            Err(e)
+                if e.downcast_ref::<std::io::Error>()
+                    .map(|e| e.kind() == std::io::ErrorKind::NotFound)
+                    .unwrap_or(false) =>
+            {
+                tracing::info!("Will create state file at {}", path.display());
+                Self {
+                    tenants: HashMap::new(),
+                    path: path.to_owned(),
+                }
+            }
+            Err(e) => {
+                panic!("Failed to load state from '{}': {e:#} (maybe your .neon/ dir was written by an older version?)", path.display())
+            }
+        }
+    }
+}
+
+/// State available to HTTP request handlers
+#[derive(Clone)]
+struct State {
+    inner: Arc<tokio::sync::RwLock<PersistentState>>,
+}
+
+impl State {
+    fn new(persistent_state: PersistentState) -> State {
+        Self {
+            inner: Arc::new(tokio::sync::RwLock::new(persistent_state)),
+        }
+    }
+}
+
+#[inline(always)]
+fn get_state(request: &Request<Body>) -> &State {
+    request
+        .data::<Arc<State>>()
+        .expect("unknown state type")
+        .as_ref()
+}
+
+/// Pageserver calls into this on startup, to learn which tenants it should attach
+async fn handle_re_attach(mut req: Request<Body>) -> Result<Response<Body>, ApiError> {
+    let reattach_req = json_request::<ReAttachRequest>(&mut req).await?;
+
+    let state = get_state(&req).inner.clone();
+    let mut locked = state.write().await;
+
+    let mut response = ReAttachResponse {
+        tenants: Vec::new(),
+    };
+    for (t, state) in &mut locked.tenants {
+        if state.pageserver == Some(reattach_req.node_id) {
+            state.generation += 1;
+            response.tenants.push(ReAttachResponseTenant {
+                id: *t,
+                generation: state.generation,
+            });
+        }
+    }
+
+    locked.save().await.map_err(ApiError::InternalServerError)?;
+
+    json_response(StatusCode::OK, response)
+}
+
+/// Pageserver calls into this before doing deletions, to confirm that it still
+/// holds the latest generation for the tenants with deletions enqueued
+async fn handle_validate(mut req: Request<Body>) -> Result<Response<Body>, ApiError> {
+    let validate_req = json_request::<ValidateRequest>(&mut req).await?;
+
+    let locked = get_state(&req).inner.read().await;
+
+    let mut response = ValidateResponse {
+        tenants: Vec::new(),
+    };
+
+    for req_tenant in validate_req.tenants {
+        if let Some(tenant_state) = locked.tenants.get(&req_tenant.id) {
+            let valid = tenant_state.generation == req_tenant.gen;
+            response.tenants.push(ValidateResponseTenant {
+                id: req_tenant.id,
+                valid,
+            });
+        }
+    }
+
+    json_response(StatusCode::OK, response)
+}
+/// Call into this before attaching a tenant to a pageserver, to acquire a generation number
+/// (in the real control plane this is unnecessary, because the same program is managing
+///  generation numbers and doing attachments).
+async fn handle_attach_hook(mut req: Request<Body>) -> Result<Response<Body>, ApiError> {
+    let attach_req = json_request::<AttachHookRequest>(&mut req).await?;
+
+    let state = get_state(&req).inner.clone();
+    let mut locked = state.write().await;
+
+    let tenant_state = locked
+        .tenants
+        .entry(attach_req.tenant_id)
+        .or_insert_with(|| TenantState {
+            pageserver: attach_req.pageserver_id,
+            generation: 0,
+        });
+
+    if attach_req.pageserver_id.is_some() {
+        tenant_state.generation += 1;
+    }
+    let generation = tenant_state.generation;
+
+    locked.save().await.map_err(ApiError::InternalServerError)?;
+
+    json_response(
+        StatusCode::OK,
+        AttachHookResponse {
+            gen: attach_req.pageserver_id.map(|_| generation),
+        },
+    )
+}
+
+fn make_router(persistent_state: PersistentState) -> RouterBuilder<hyper::Body, ApiError> {
+    endpoint::make_router()
+        .data(Arc::new(State::new(persistent_state)))
+        .post("/re-attach", handle_re_attach)
+        .post("/validate", handle_validate)
+        .post("/attach_hook", handle_attach_hook)
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    logging::init(
+        LogFormat::Plain,
+        logging::TracingErrorLayerEnablement::Disabled,
+    )?;
+
+    let args = Cli::parse();
+    tracing::info!(
+        "Starting, state at {}, listening on {}",
+        args.path.to_string_lossy(),
+        args.listen
+    );
+
+    let persistent_state = PersistentState::load_or_new(&args.path).await;
+
+    let http_listener = tcp_listener::bind(args.listen)?;
+    let router = make_router(persistent_state)
+        .build()
+        .map_err(|err| anyhow!(err))?;
+    let service = utils::http::RouterService::new(router).unwrap();
+    let server = hyper::Server::from_tcp(http_listener)?.serve(service);
+
+    tracing::info!("Serving on {0}", args.listen);
+    server.await?;
+
+    Ok(())
+}
--- a/control_plane/src/bin/neon_local.rs
+++ b/control_plane/src/bin/neon_local.rs
@@ -8,6 +8,7 @@
 use anyhow::{anyhow, bail, Context, Result};
 use clap::{value_parser, Arg, ArgAction, ArgMatches, Command};
 use compute_api::spec::ComputeMode;
+use control_plane::attachment_service::AttachmentService;
 use control_plane::endpoint::ComputeControlPlane;
 use control_plane::local_env::LocalEnv;
 use control_plane::pageserver::PageServerNode;
@@ -43,14 +44,18 @@ project_git_version!(GIT_VERSION);

 const DEFAULT_PG_VERSION: &str = "15";

+const DEFAULT_PAGESERVER_CONTROL_PLANE_API: &str = "http://127.0.0.1:1234/";
+
 fn default_conf() -> String {
    format!(
        r#"
 # Default built-in configuration, defined in main.rs
+control_plane_api = '{DEFAULT_PAGESERVER_CONTROL_PLANE_API}'
+
 [broker]
 listen_addr = '{DEFAULT_BROKER_ADDR}'

-[pageserver]
+[[pageservers]]
 id = {DEFAULT_PAGESERVER_ID}
 listen_pg_addr = '{DEFAULT_PAGESERVER_PG_ADDR}'
 listen_http_addr = '{DEFAULT_PAGESERVER_HTTP_ADDR}'
@@ -61,6 +66,7 @@ http_auth_type = '{trust_auth}'
 id = {DEFAULT_SAFEKEEPER_ID}
 pg_port = {DEFAULT_SAFEKEEPER_PG_PORT}
 http_port = {DEFAULT_SAFEKEEPER_HTTP_PORT}
+
 "#,
        trust_auth = AuthType::Trust,
    )
@@ -107,6 +113,7 @@ fn main() -> Result<()> {
            "start" => handle_start_all(sub_args, &env),
            "stop" => handle_stop_all(sub_args, &env),
            "pageserver" => handle_pageserver(sub_args, &env),
+            "attachment_service" => handle_attachment_service(sub_args, &env),
            "safekeeper" => handle_safekeeper(sub_args, &env),
            "endpoint" => handle_endpoint(sub_args, &env),
            "pg" => bail!("'pg' subcommand has been renamed to 'endpoint'"),
@@ -252,7 +259,7 @@ fn get_timeline_infos(
    env: &local_env::LocalEnv,
    tenant_id: &TenantId,
 ) -> Result<HashMap<TimelineId, TimelineInfo>> {
-    Ok(PageServerNode::from_env(env)
+    Ok(get_default_pageserver(env)
        .timeline_list(tenant_id)?
        .into_iter()
        .map(|timeline_info| (timeline_info.timeline_id, timeline_info))
@@ -313,17 +320,30 @@ fn handle_init(init_match: &ArgMatches) -> anyhow::Result<LocalEnv> {
        .context("Failed to initialize neon repository")?;

    // Initialize pageserver, create initial tenant and timeline.
-    let pageserver = PageServerNode::from_env(&env);
-    pageserver
-        .initialize(&pageserver_config_overrides(init_match))
-        .unwrap_or_else(|e| {
-            eprintln!("pageserver init failed: {e:?}");
-            exit(1);
-        });
+    for ps_conf in &env.pageservers {
+        PageServerNode::from_env(&env, ps_conf)
+            .initialize(&pageserver_config_overrides(init_match))
+            .unwrap_or_else(|e| {
+                eprintln!("pageserver init failed: {e:?}");
+                exit(1);
+            });
+    }

    Ok(env)
 }

+/// The default pageserver is the one where CLI tenant/timeline operations are sent by default.
+/// For typical interactive use, one would just run with a single pageserver.  Scenarios with
+/// tenant/timeline placement across multiple pageservers are managed by python test code rather
+/// than this CLI.
+fn get_default_pageserver(env: &local_env::LocalEnv) -> PageServerNode {
+    let ps_conf = env
+        .pageservers
+        .first()
+        .expect("Config is validated to contain at least one pageserver");
+    PageServerNode::from_env(env, ps_conf)
+}
+
 fn pageserver_config_overrides(init_match: &ArgMatches) -> Vec<&str> {
    init_match
        .get_many::<String>("pageserver-config-override")
@@ -334,7 +354,7 @@ fn pageserver_config_overrides(init_match: &ArgMatches) -> Vec<&str> {
 }

 fn handle_tenant(tenant_match: &ArgMatches, env: &mut local_env::LocalEnv) -> anyhow::Result<()> {
-    let pageserver = PageServerNode::from_env(env);
+    let pageserver = get_default_pageserver(env);
    match tenant_match.subcommand() {
        Some(("list", _)) => {
            for t in pageserver.tenant_list()? {
@@ -342,13 +362,25 @@ fn handle_tenant(tenant_match: &ArgMatches, env: &mut local_env::LocalEnv) -> an
            }
        }
        Some(("create", create_match)) => {
-            let initial_tenant_id = parse_tenant_id(create_match)?;
            let tenant_conf: HashMap<_, _> = create_match
                .get_many::<String>("config")
                .map(|vals| vals.flat_map(|c| c.split_once(':')).collect())
                .unwrap_or_default();
-            let new_tenant_id = pageserver.tenant_create(initial_tenant_id, tenant_conf)?;
-            println!("tenant {new_tenant_id} successfully created on the pageserver");
+
+            // If tenant ID was not specified, generate one
+            let tenant_id = parse_tenant_id(create_match)?.unwrap_or_else(TenantId::generate);
+
+            let generation = if env.control_plane_api.is_some() {
+                // We must register the tenant with the attachment service, so
+                // that when the pageserver restarts, it will be re-attached.
+                let attachment_service = AttachmentService::from_env(env);
+                attachment_service.attach_hook(tenant_id, pageserver.conf.id)?
+            } else {
+                None
+            };
+
+            pageserver.tenant_create(tenant_id, generation, tenant_conf)?;
+            println!("tenant {tenant_id} successfully created on the pageserver");

            // Create an initial timeline for the new tenant
            let new_timeline_id = parse_timeline_id(create_match)?;
@@ -358,7 +390,7 @@ fn handle_tenant(tenant_match: &ArgMatches, env: &mut local_env::LocalEnv) -> an
                .context("Failed to parse postgres version from the argument string")?;

            let timeline_info = pageserver.timeline_create(
-                new_tenant_id,
+                tenant_id,
                new_timeline_id,
                None,
                None,
@@ -369,17 +401,17 @@ fn handle_tenant(tenant_match: &ArgMatches, env: &mut local_env::LocalEnv) -> an

            env.register_branch_mapping(
                DEFAULT_BRANCH_NAME.to_string(),
-                new_tenant_id,
+                tenant_id,
                new_timeline_id,
            )?;

            println!(
-                "Created an initial timeline '{new_timeline_id}' at Lsn {last_record_lsn} for tenant: {new_tenant_id}",
+                "Created an initial timeline '{new_timeline_id}' at Lsn {last_record_lsn} for tenant: {tenant_id}",
            );

            if create_match.get_flag("set-default") {
-                println!("Setting tenant {new_tenant_id} as a default one");
-                env.default_tenant_id = Some(new_tenant_id);
+                println!("Setting tenant {tenant_id} as a default one");
+                env.default_tenant_id = Some(tenant_id);
            }
        }
        Some(("set-default", set_default_match)) => {
@@ -407,7 +439,7 @@ fn handle_tenant(tenant_match: &ArgMatches, env: &mut local_env::LocalEnv) -> an
 }

 fn handle_timeline(timeline_match: &ArgMatches, env: &mut local_env::LocalEnv) -> Result<()> {
-    let pageserver = PageServerNode::from_env(env);
+    let pageserver = get_default_pageserver(env);

    match timeline_match.subcommand() {
        Some(("list", list_match)) => {
@@ -484,6 +516,7 @@ fn handle_timeline(timeline_match: &ArgMatches, env: &mut local_env::LocalEnv) -
                None,
                pg_version,
                ComputeMode::Primary,
+                DEFAULT_PAGESERVER_ID,
            )?;
            println!("Done");
        }
@@ -537,7 +570,6 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(
        Some(ep_subcommand_data) => ep_subcommand_data,
        None => bail!("no endpoint subcommand provided"),
    };
-
    let mut cplane = ComputeControlPlane::load(env.clone())?;

    // All subcommands take an optional --tenant-id option
@@ -634,6 +666,13 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(
                .copied()
                .unwrap_or(false);

+            let pageserver_id =
+                if let Some(id_str) = sub_args.get_one::<String>("endpoint-pageserver-id") {
+                    NodeId(id_str.parse().context("while parsing pageserver id")?)
+                } else {
+                    DEFAULT_PAGESERVER_ID
+                };
+
            let mode = match (lsn, hot_standby) {
                (Some(lsn), false) => ComputeMode::Static(lsn),
                (None, true) => ComputeMode::Replica,
@@ -649,6 +688,7 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(
                http_port,
                pg_version,
                mode,
+                pageserver_id,
            )?;
        }
        "start" => {
@@ -658,6 +698,13 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(
                .get_one::<String>("endpoint_id")
                .ok_or_else(|| anyhow!("No endpoint ID was provided to start"))?;

+            let pageserver_id =
+                if let Some(id_str) = sub_args.get_one::<String>("endpoint-pageserver-id") {
+                    NodeId(id_str.parse().context("while parsing pageserver id")?)
+                } else {
+                    DEFAULT_PAGESERVER_ID
+                };
+
            let remote_ext_config = sub_args.get_one::<String>("remote-ext-config");

            // If --safekeepers argument is given, use only the listed safekeeper nodes.
@@ -677,7 +724,8 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(

            let endpoint = cplane.endpoints.get(endpoint_id.as_str());

-            let auth_token = if matches!(env.pageserver.pg_auth_type, AuthType::NeonJWT) {
+            let ps_conf = env.get_pageserver_conf(pageserver_id)?;
+            let auth_token = if matches!(ps_conf.pg_auth_type, AuthType::NeonJWT) {
                let claims = Claims::new(Some(tenant_id), Scope::Tenant);

                Some(env.generate_auth_token(&claims)?)
@@ -744,6 +792,7 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(
                    http_port,
                    pg_version,
                    mode,
+                    pageserver_id,
                )?;
                ep.start(&auth_token, safekeepers, remote_ext_config)?;
            }
@@ -768,51 +817,94 @@ fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<(
 }

 fn handle_pageserver(sub_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<()> {
-    let pageserver = PageServerNode::from_env(env);
+    fn get_pageserver(env: &local_env::LocalEnv, args: &ArgMatches) -> Result<PageServerNode> {
+        let node_id = if let Some(id_str) = args.get_one::<String>("pageserver-id") {
+            NodeId(id_str.parse().context("while parsing pageserver id")?)
+        } else {
+            DEFAULT_PAGESERVER_ID
+        };
+
+        Ok(PageServerNode::from_env(
+            env,
+            env.get_pageserver_conf(node_id)?,
+        ))
+    }

    match sub_match.subcommand() {
-        Some(("start", start_match)) => {
-            if let Err(e) = pageserver.start(&pageserver_config_overrides(start_match)) {
+        Some(("start", subcommand_args)) => {
+            if let Err(e) = get_pageserver(env, subcommand_args)?
+                .start(&pageserver_config_overrides(subcommand_args))
+            {
                eprintln!("pageserver start failed: {e}");
                exit(1);
            }
        }

+        Some(("stop", subcommand_args)) => {
+            let immediate = subcommand_args
+                .get_one::<String>("stop-mode")
+                .map(|s| s.as_str())
+                == Some("immediate");
+
+            if let Err(e) = get_pageserver(env, subcommand_args)?.stop(immediate) {
+                eprintln!("pageserver stop failed: {}", e);
+                exit(1);
+            }
+        }
+
+        Some(("restart", subcommand_args)) => {
+            let pageserver = get_pageserver(env, subcommand_args)?;
+            //TODO what shutdown strategy should we use here?
+            if let Err(e) = pageserver.stop(false) {
+                eprintln!("pageserver stop failed: {}", e);
+                exit(1);
+            }
+
+            if let Err(e) = pageserver.start(&pageserver_config_overrides(subcommand_args)) {
+                eprintln!("pageserver start failed: {e}");
+                exit(1);
+            }
+        }
+
+        Some(("status", subcommand_args)) => {
+            match get_pageserver(env, subcommand_args)?.check_status() {
+                Ok(_) => println!("Page server is up and running"),
+                Err(err) => {
+                    eprintln!("Page server is not available: {}", err);
+                    exit(1);
+                }
+            }
+        }
+
+        Some((sub_name, _)) => bail!("Unexpected pageserver subcommand '{}'", sub_name),
+        None => bail!("no pageserver subcommand provided"),
+    }
+    Ok(())
+}
+
+fn handle_attachment_service(sub_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<()> {
+    let svc = AttachmentService::from_env(env);
+    match sub_match.subcommand() {
+        Some(("start", _start_match)) => {
+            if let Err(e) = svc.start() {
+                eprintln!("start failed: {e}");
+                exit(1);
+            }
+        }
+
        Some(("stop", stop_match)) => {
            let immediate = stop_match
                .get_one::<String>("stop-mode")
                .map(|s| s.as_str())
                == Some("immediate");

-            if let Err(e) = pageserver.stop(immediate) {
-                eprintln!("pageserver stop failed: {}", e);
+            if let Err(e) = svc.stop(immediate) {
+                eprintln!("stop failed: {}", e);
                exit(1);
            }
        }
-
-        Some(("restart", restart_match)) => {
-            //TODO what shutdown strategy should we use here?
-            if let Err(e) = pageserver.stop(false) {
-                eprintln!("pageserver stop failed: {}", e);
-                exit(1);
-            }
-
-            if let Err(e) = pageserver.start(&pageserver_config_overrides(restart_match)) {
-                eprintln!("pageserver start failed: {e}");
-                exit(1);
-            }
-        }
-
-        Some(("status", _)) => match PageServerNode::from_env(env).check_status() {
-            Ok(_) => println!("Page server is up and running"),
-            Err(err) => {
-                eprintln!("Page server is not available: {}", err);
-                exit(1);
-            }
-        },
-
-        Some((sub_name, _)) => bail!("Unexpected pageserver subcommand '{}'", sub_name),
-        None => bail!("no pageserver subcommand provided"),
+        Some((sub_name, _)) => bail!("Unexpected attachment_service subcommand '{}'", sub_name),
+        None => bail!("no attachment_service subcommand provided"),
    }
    Ok(())
 }
@@ -897,11 +989,23 @@ fn handle_start_all(sub_match: &ArgMatches, env: &local_env::LocalEnv) -> anyhow

    broker::start_broker_process(env)?;

-    let pageserver = PageServerNode::from_env(env);
-    if let Err(e) = pageserver.start(&pageserver_config_overrides(sub_match)) {
-        eprintln!("pageserver {} start failed: {:#}", env.pageserver.id, e);
-        try_stop_all(env, true);
-        exit(1);
+    // Only start the attachment service if the pageserver is configured to need it
+    if env.control_plane_api.is_some() {
+        let attachment_service = AttachmentService::from_env(env);
+        if let Err(e) = attachment_service.start() {
+            eprintln!("attachment_service start failed: {:#}", e);
+            try_stop_all(env, true);
+            exit(1);
+        }
+    }
+
+    for ps_conf in &env.pageservers {
+        let pageserver = PageServerNode::from_env(env, ps_conf);
+        if let Err(e) = pageserver.start(&pageserver_config_overrides(sub_match)) {
+            eprintln!("pageserver {} start failed: {:#}", ps_conf.id, e);
+            try_stop_all(env, true);
+            exit(1);
+        }
    }

    for node in env.safekeepers.iter() {
@@ -925,8 +1029,6 @@ fn handle_stop_all(sub_match: &ArgMatches, env: &local_env::LocalEnv) -> Result<
 }

 fn try_stop_all(env: &local_env::LocalEnv, immediate: bool) {
-    let pageserver = PageServerNode::from_env(env);
-
    // Stop all endpoints
    match ComputeControlPlane::load(env.clone()) {
        Ok(cplane) => {
@@ -941,8 +1043,11 @@ fn try_stop_all(env: &local_env::LocalEnv, immediate: bool) {
        }
    }

-    if let Err(e) = pageserver.stop(immediate) {
-        eprintln!("pageserver {} stop failed: {:#}", env.pageserver.id, e);
+    for ps_conf in &env.pageservers {
+        let pageserver = PageServerNode::from_env(env, ps_conf);
+        if let Err(e) = pageserver.stop(immediate) {
+            eprintln!("pageserver {} stop failed: {:#}", ps_conf.id, e);
+        }
    }

    for node in env.safekeepers.iter() {
@@ -955,6 +1060,13 @@ fn try_stop_all(env: &local_env::LocalEnv, immediate: bool) {
    if let Err(e) = broker::stop_broker_process(env) {
        eprintln!("neon broker stop failed: {e:#}");
    }
+
+    if env.control_plane_api.is_some() {
+        let attachment_service = AttachmentService::from_env(env);
+        if let Err(e) = attachment_service.stop(immediate) {
+            eprintln!("attachment service stop failed: {e:#}");
+        }
+    }
 }

 fn cli() -> Command {
@@ -969,6 +1081,16 @@ fn cli() -> Command {

    let safekeeper_id_arg = Arg::new("id").help("safekeeper id").required(false);

+    // --id, when using a pageserver command
+    let pageserver_id_arg = Arg::new("pageserver-id")
+        .long("id")
+        .help("pageserver id")
+        .required(false);
+    // --pageserver-id when using a non-pageserver command
+    let endpoint_pageserver_id_arg = Arg::new("endpoint-pageserver-id")
+        .long("pageserver-id")
+        .required(false);
+
    let safekeeper_extra_opt_arg = Arg::new("safekeeper-extra-opt")
        .short('e')
        .long("safekeeper-extra-opt")
@@ -1133,10 +1255,24 @@ fn cli() -> Command {
                .arg_required_else_help(true)
                .about("Manage pageserver")
                .subcommand(Command::new("status"))
+                .arg(pageserver_id_arg.clone())
+                .subcommand(Command::new("start").about("Start local pageserver")
+                .arg(pageserver_id_arg.clone())
+                .arg(pageserver_config_args.clone()))
+                .subcommand(Command::new("stop").about("Stop local pageserver")
+                .arg(pageserver_id_arg.clone())
+                            .arg(stop_mode_arg.clone()))
+                .subcommand(Command::new("restart").about("Restart local pageserver")
+                .arg(pageserver_id_arg.clone())
+                .arg(pageserver_config_args.clone()))
+        )
+        .subcommand(
+            Command::new("attachment_service")
+                .arg_required_else_help(true)
+                .about("Manage attachment_service")
                .subcommand(Command::new("start").about("Start local pageserver").arg(pageserver_config_args.clone()))
                .subcommand(Command::new("stop").about("Stop local pageserver")
                            .arg(stop_mode_arg.clone()))
-                .subcommand(Command::new("restart").about("Restart local pageserver").arg(pageserver_config_args.clone()))
        )
        .subcommand(
            Command::new("safekeeper")
@@ -1172,6 +1308,7 @@ fn cli() -> Command {
                    .arg(lsn_arg.clone())
                    .arg(pg_port_arg.clone())
                    .arg(http_port_arg.clone())
+                    .arg(endpoint_pageserver_id_arg.clone())
                    .arg(
                        Arg::new("config-only")
                            .help("Don't do basebackup, create endpoint directory with only config files")
@@ -1189,6 +1326,7 @@ fn cli() -> Command {
                    .arg(lsn_arg)
                    .arg(pg_port_arg)
                    .arg(http_port_arg)
+                    .arg(endpoint_pageserver_id_arg.clone())
                    .arg(pg_version_arg)
                    .arg(hot_standby_arg)
                    .arg(safekeepers_arg)
--- a/control_plane/src/endpoint.rs
+++ b/control_plane/src/endpoint.rs
@@ -70,6 +70,7 @@ pub struct EndpointConf {
    http_port: u16,
    pg_version: u32,
    skip_pg_catalog_updates: bool,
+    pageserver_id: NodeId,
 }

 //
@@ -82,19 +83,16 @@ pub struct ComputeControlPlane {
    pub endpoints: BTreeMap<String, Arc<Endpoint>>,

    env: LocalEnv,
-    pageserver: Arc<PageServerNode>,
 }

 impl ComputeControlPlane {
    // Load current endpoints from the endpoints/ subdirectories
    pub fn load(env: LocalEnv) -> Result<ComputeControlPlane> {
-        let pageserver = Arc::new(PageServerNode::from_env(&env));
-
        let mut endpoints = BTreeMap::default();
        for endpoint_dir in std::fs::read_dir(env.endpoints_path())
            .with_context(|| format!("failed to list {}", env.endpoints_path().display()))?
        {
-            let ep = Endpoint::from_dir_entry(endpoint_dir?, &env, &pageserver)?;
+            let ep = Endpoint::from_dir_entry(endpoint_dir?, &env)?;
            endpoints.insert(ep.endpoint_id.clone(), Arc::new(ep));
        }

@@ -102,7 +100,6 @@ impl ComputeControlPlane {
            base_port: 55431,
            endpoints,
            env,
-            pageserver,
        })
    }

@@ -125,20 +122,29 @@ impl ComputeControlPlane {
        http_port: Option<u16>,
        pg_version: u32,
        mode: ComputeMode,
+        pageserver_id: NodeId,
    ) -> Result<Arc<Endpoint>> {
        let pg_port = pg_port.unwrap_or_else(|| self.get_port());
        let http_port = http_port.unwrap_or_else(|| self.get_port() + 1);
+        let pageserver =
+            PageServerNode::from_env(&self.env, self.env.get_pageserver_conf(pageserver_id)?);
        let ep = Arc::new(Endpoint {
            endpoint_id: endpoint_id.to_owned(),
            pg_address: SocketAddr::new("127.0.0.1".parse().unwrap(), pg_port),
            http_address: SocketAddr::new("127.0.0.1".parse().unwrap(), http_port),
            env: self.env.clone(),
-            pageserver: Arc::clone(&self.pageserver),
+            pageserver,
            timeline_id,
            mode,
            tenant_id,
            pg_version,
-            skip_pg_catalog_updates: false,
+            // We don't setup roles and databases in the spec locally, so we don't need to
+            // do catalog updates. Catalog updates also include check availability
+            // data creation. Yet, we have tests that check that size and db dump
+            // before and after start are the same. So, skip catalog updates,
+            // with this we basically test a case of waking up an idle compute, where
+            // we also skip catalog updates in the cloud.
+            skip_pg_catalog_updates: true,
        });

        ep.create_endpoint_dir()?;
@@ -152,7 +158,8 @@ impl ComputeControlPlane {
                http_port,
                pg_port,
                pg_version,
-                skip_pg_catalog_updates: false,
+                skip_pg_catalog_updates: true,
+                pageserver_id,
            })?,
        )?;
        std::fs::write(
@@ -187,18 +194,14 @@ pub struct Endpoint {
    // These are not part of the endpoint as such, but the environment
    // the endpoint runs in.
    pub env: LocalEnv,
-    pageserver: Arc<PageServerNode>,
+    pageserver: PageServerNode,

    // Optimizations
    skip_pg_catalog_updates: bool,
 }

 impl Endpoint {
-    fn from_dir_entry(
-        entry: std::fs::DirEntry,
-        env: &LocalEnv,
-        pageserver: &Arc<PageServerNode>,
-    ) -> Result<Endpoint> {
+    fn from_dir_entry(entry: std::fs::DirEntry, env: &LocalEnv) -> Result<Endpoint> {
        if !entry.file_type()?.is_dir() {
            anyhow::bail!(
                "Endpoint::from_dir_entry failed: '{}' is not a directory",
@@ -214,12 +217,15 @@ impl Endpoint {
        let conf: EndpointConf =
            serde_json::from_slice(&std::fs::read(entry.path().join("endpoint.json"))?)?;

+        let pageserver =
+            PageServerNode::from_env(env, env.get_pageserver_conf(conf.pageserver_id)?);
+
        Ok(Endpoint {
            pg_address: SocketAddr::new("127.0.0.1".parse().unwrap(), conf.pg_port),
            http_address: SocketAddr::new("127.0.0.1".parse().unwrap(), conf.http_port),
            endpoint_id,
            env: env.clone(),
-            pageserver: Arc::clone(pageserver),
+            pageserver,
            timeline_id: conf.timeline_id,
            mode: conf.mode,
            tenant_id: conf.tenant_id,
--- a/control_plane/src/lib.rs
+++ b/control_plane/src/lib.rs
@@ -7,6 +7,7 @@
 // local installations.
 //

+pub mod attachment_service;
 mod background_process;
 pub mod broker;
 pub mod endpoint;
--- a/control_plane/src/local_env.rs
+++ b/control_plane/src/local_env.rs
@@ -68,11 +68,17 @@ pub struct LocalEnv {

    pub broker: NeonBroker,

-    pub pageserver: PageServerConf,
+    /// This Vec must always contain at least one pageserver
+    pub pageservers: Vec<PageServerConf>,

    #[serde(default)]
    pub safekeepers: Vec<SafekeeperConf>,

+    // Control plane location: if None, we will not run attachment_service.  If set, this will
+    // be propagated into each pageserver's configuration.
+    #[serde(default)]
+    pub control_plane_api: Option<Url>,
+
    /// Keep human-readable aliases in memory (and persist them to config), to hide ZId hex strings from the user.
    #[serde(default)]
    // A `HashMap<String, HashMap<TenantId, TimelineId>>` would be more appropriate here,
@@ -176,32 +182,28 @@ impl LocalEnv {
    pub fn pg_distrib_dir(&self, pg_version: u32) -> anyhow::Result<PathBuf> {
        let path = self.pg_distrib_dir.clone();

+        #[allow(clippy::manual_range_patterns)]
        match pg_version {
-            14 => Ok(path.join(format!("v{pg_version}"))),
-            15 => Ok(path.join(format!("v{pg_version}"))),
+            14 | 15 | 16 => Ok(path.join(format!("v{pg_version}"))),
            _ => bail!("Unsupported postgres version: {}", pg_version),
        }
    }

    pub fn pg_bin_dir(&self, pg_version: u32) -> anyhow::Result<PathBuf> {
-        match pg_version {
-            14 => Ok(self.pg_distrib_dir(pg_version)?.join("bin")),
-            15 => Ok(self.pg_distrib_dir(pg_version)?.join("bin")),
-            _ => bail!("Unsupported postgres version: {}", pg_version),
-        }
+        Ok(self.pg_distrib_dir(pg_version)?.join("bin"))
    }
    pub fn pg_lib_dir(&self, pg_version: u32) -> anyhow::Result<PathBuf> {
-        match pg_version {
-            14 => Ok(self.pg_distrib_dir(pg_version)?.join("lib")),
-            15 => Ok(self.pg_distrib_dir(pg_version)?.join("lib")),
-            _ => bail!("Unsupported postgres version: {}", pg_version),
-        }
+        Ok(self.pg_distrib_dir(pg_version)?.join("lib"))
    }

    pub fn pageserver_bin(&self) -> PathBuf {
        self.neon_distrib_dir.join("pageserver")
    }

+    pub fn attachment_service_bin(&self) -> PathBuf {
+        self.neon_distrib_dir.join("attachment_service")
+    }
+
    pub fn safekeeper_bin(&self) -> PathBuf {
        self.neon_distrib_dir.join("safekeeper")
    }
@@ -214,15 +216,23 @@ impl LocalEnv {
        self.base_data_dir.join("endpoints")
    }

-    // TODO: move pageserver files into ./pageserver
-    pub fn pageserver_data_dir(&self) -> PathBuf {
-        self.base_data_dir.clone()
+    pub fn pageserver_data_dir(&self, pageserver_id: NodeId) -> PathBuf {
+        self.base_data_dir
+            .join(format!("pageserver_{pageserver_id}"))
    }

    pub fn safekeeper_data_dir(&self, data_dir_name: &str) -> PathBuf {
        self.base_data_dir.join("safekeepers").join(data_dir_name)
    }

+    pub fn get_pageserver_conf(&self, id: NodeId) -> anyhow::Result<&PageServerConf> {
+        if let Some(conf) = self.pageservers.iter().find(|node| node.id == id) {
+            Ok(conf)
+        } else {
+            bail!("could not find pageserver {id}")
+        }
+    }
+
    pub fn register_branch_mapping(
        &mut self,
        branch_name: String,
@@ -299,6 +309,10 @@ impl LocalEnv {
            env.neon_distrib_dir = env::current_exe()?.parent().unwrap().to_owned();
        }

+        if env.pageservers.is_empty() {
+            anyhow::bail!("Configuration must contain at least one pageserver");
+        }
+
        env.base_data_dir = base_path();

        Ok(env)
@@ -331,7 +345,7 @@ impl LocalEnv {
        // We read that in, in `create_config`, and fill any missing defaults. Then it's saved
        // to .neon/config. TODO: We lose any formatting and comments along the way, which is
        // a bit sad.
-        let mut conf_content = r#"# This file describes a locale deployment of the page server
+        let mut conf_content = r#"# This file describes a local deployment of the page server
 # and safekeeeper node. It is read by the 'neon_local' command-line
 # utility.
 "#
@@ -461,9 +475,9 @@ impl LocalEnv {
    }

    fn auth_keys_needed(&self) -> bool {
-        self.pageserver.pg_auth_type == AuthType::NeonJWT
-            || self.pageserver.http_auth_type == AuthType::NeonJWT
-            || self.safekeepers.iter().any(|sk| sk.auth_enabled)
+        self.pageservers.iter().any(|ps| {
+            ps.pg_auth_type == AuthType::NeonJWT || ps.http_auth_type == AuthType::NeonJWT
+        }) || self.safekeepers.iter().any(|sk| sk.auth_enabled)
    }
 }

--- a/control_plane/src/pageserver.rs
+++ b/control_plane/src/pageserver.rs
@@ -27,6 +27,7 @@ use utils::{
    lsn::Lsn,
 };

+use crate::local_env::PageServerConf;
 use crate::{background_process, local_env::LocalEnv};

 #[derive(Error, Debug)]
@@ -76,43 +77,40 @@ impl ResponseErrorMessageExt for Response {
 #[derive(Debug)]
 pub struct PageServerNode {
    pub pg_connection_config: PgConnectionConfig,
+    pub conf: PageServerConf,
    pub env: LocalEnv,
    pub http_client: Client,
    pub http_base_url: String,
 }

 impl PageServerNode {
-    pub fn from_env(env: &LocalEnv) -> PageServerNode {
-        let (host, port) = parse_host_port(&env.pageserver.listen_pg_addr)
-            .expect("Unable to parse listen_pg_addr");
+    pub fn from_env(env: &LocalEnv, conf: &PageServerConf) -> PageServerNode {
+        let (host, port) =
+            parse_host_port(&conf.listen_pg_addr).expect("Unable to parse listen_pg_addr");
        let port = port.unwrap_or(5432);
        Self {
            pg_connection_config: PgConnectionConfig::new_host_port(host, port),
+            conf: conf.clone(),
            env: env.clone(),
            http_client: Client::new(),
-            http_base_url: format!("http://{}/v1", env.pageserver.listen_http_addr),
+            http_base_url: format!("http://{}/v1", conf.listen_http_addr),
        }
    }

    // pageserver conf overrides defined by neon_local configuration.
    fn neon_local_overrides(&self) -> Vec<String> {
-        let id = format!("id={}", self.env.pageserver.id);
+        let id = format!("id={}", self.conf.id);
        // FIXME: the paths should be shell-escaped to handle paths with spaces, quotas etc.
        let pg_distrib_dir_param = format!(
            "pg_distrib_dir='{}'",
            self.env.pg_distrib_dir_raw().display()
        );

-        let http_auth_type_param =
-            format!("http_auth_type='{}'", self.env.pageserver.http_auth_type);
-        let listen_http_addr_param = format!(
-            "listen_http_addr='{}'",
-            self.env.pageserver.listen_http_addr
-        );
+        let http_auth_type_param = format!("http_auth_type='{}'", self.conf.http_auth_type);
+        let listen_http_addr_param = format!("listen_http_addr='{}'", self.conf.listen_http_addr);

-        let pg_auth_type_param = format!("pg_auth_type='{}'", self.env.pageserver.pg_auth_type);
-        let listen_pg_addr_param =
-            format!("listen_pg_addr='{}'", self.env.pageserver.listen_pg_addr);
+        let pg_auth_type_param = format!("pg_auth_type='{}'", self.conf.pg_auth_type);
+        let listen_pg_addr_param = format!("listen_pg_addr='{}'", self.conf.listen_pg_addr);

        let broker_endpoint_param = format!("broker_endpoint='{}'", self.env.broker.client_url());

@@ -126,10 +124,18 @@ impl PageServerNode {
            broker_endpoint_param,
        ];

-        if self.env.pageserver.http_auth_type != AuthType::Trust
-            || self.env.pageserver.pg_auth_type != AuthType::Trust
+        if let Some(control_plane_api) = &self.env.control_plane_api {
+            overrides.push(format!(
+                "control_plane_api='{}'",
+                control_plane_api.as_str()
+            ));
+        }
+
+        if self.conf.http_auth_type != AuthType::Trust || self.conf.pg_auth_type != AuthType::Trust
        {
-            overrides.push("auth_validation_public_key_path='auth_public_key.pem'".to_owned());
+            // Keys are generated in the toplevel repo dir, pageservers' workdirs
+            // are one level below that, so refer to keys with ../
+            overrides.push("auth_validation_public_key_path='../auth_public_key.pem'".to_owned());
        }
        overrides
    }
@@ -137,16 +143,12 @@ impl PageServerNode {
    /// Initializes a pageserver node by creating its config with the overrides provided.
    pub fn initialize(&self, config_overrides: &[&str]) -> anyhow::Result<()> {
        // First, run `pageserver --init` and wait for it to write a config into FS and exit.
-        self.pageserver_init(config_overrides).with_context(|| {
-            format!(
-                "Failed to run init for pageserver node {}",
-                self.env.pageserver.id,
-            )
-        })
+        self.pageserver_init(config_overrides)
+            .with_context(|| format!("Failed to run init for pageserver node {}", self.conf.id,))
    }

    pub fn repo_path(&self) -> PathBuf {
-        self.env.pageserver_data_dir()
+        self.env.pageserver_data_dir(self.conf.id)
    }

    /// The pid file is created by the pageserver process, with its pid stored inside.
@@ -162,7 +164,7 @@ impl PageServerNode {

    fn pageserver_init(&self, config_overrides: &[&str]) -> anyhow::Result<()> {
        let datadir = self.repo_path();
-        let node_id = self.env.pageserver.id;
+        let node_id = self.conf.id;
        println!(
            "Initializing pageserver node {} at '{}' in {:?}",
            node_id,
@@ -171,6 +173,10 @@ impl PageServerNode {
        );
        io::stdout().flush()?;

+        if !datadir.exists() {
+            std::fs::create_dir(&datadir)?;
+        }
+
        let datadir_path_str = datadir.to_str().with_context(|| {
            format!("Cannot start pageserver node {node_id} in path that has no string representation: {datadir:?}")
        })?;
@@ -201,7 +207,7 @@ impl PageServerNode {
        let datadir = self.repo_path();
        print!(
            "Starting pageserver node {} at '{}' in {:?}",
-            self.env.pageserver.id,
+            self.conf.id,
            self.pg_connection_config.raw_address(),
            datadir
        );
@@ -210,7 +216,7 @@ impl PageServerNode {
        let datadir_path_str = datadir.to_str().with_context(|| {
            format!(
                "Cannot start pageserver node {} in path that has no string representation: {:?}",
-                self.env.pageserver.id, datadir,
+                self.conf.id, datadir,
            )
        })?;
        let mut args = self.pageserver_basic_args(config_overrides, datadir_path_str);
@@ -254,7 +260,7 @@ impl PageServerNode {
        // FIXME: why is this tied to pageserver's auth type? Whether or not the safekeeper
        // needs a token, and how to generate that token, seems independent to whether
        // the pageserver requires a token in incoming requests.
-        Ok(if self.env.pageserver.http_auth_type != AuthType::Trust {
+        Ok(if self.conf.http_auth_type != AuthType::Trust {
            // Generate a token to connect from the pageserver to a safekeeper
            let token = self
                .env
@@ -279,7 +285,7 @@ impl PageServerNode {

    pub fn page_server_psql_client(&self) -> anyhow::Result<postgres::Client> {
        let mut config = self.pg_connection_config.clone();
-        if self.env.pageserver.pg_auth_type == AuthType::NeonJWT {
+        if self.conf.pg_auth_type == AuthType::NeonJWT {
            let token = self
                .env
                .generate_auth_token(&Claims::new(None, Scope::PageServerApi))?;
@@ -290,7 +296,7 @@ impl PageServerNode {

    fn http_request<U: IntoUrl>(&self, method: Method, url: U) -> anyhow::Result<RequestBuilder> {
        let mut builder = self.http_client.request(method, url);
-        if self.env.pageserver.http_auth_type == AuthType::NeonJWT {
+        if self.conf.http_auth_type == AuthType::NeonJWT {
            let token = self
                .env
                .generate_auth_token(&Claims::new(None, Scope::PageServerApi))?;
@@ -316,7 +322,8 @@ impl PageServerNode {

    pub fn tenant_create(
        &self,
-        new_tenant_id: Option<TenantId>,
+        new_tenant_id: TenantId,
+        generation: Option<u32>,
        settings: HashMap<&str, &str>,
    ) -> anyhow::Result<TenantId> {
        let mut settings = settings.clone();
@@ -382,11 +389,9 @@ impl PageServerNode {
                .context("Failed to parse 'gc_feedback' as bool")?,
        };

-        // If tenant ID was not specified, generate one
-        let new_tenant_id = new_tenant_id.unwrap_or(TenantId::generate());
-
        let request = models::TenantCreateRequest {
            new_tenant_id,
+            generation,
            config,
        };
        if !settings.is_empty() {
--- a/docker-compose/docker_compose_test.sh
+++ b/docker-compose/docker_compose_test.sh
@@ -30,7 +30,7 @@ cleanup() {
 echo "clean up containers if exists"
 cleanup

-for pg_version in 14 15; do
+for pg_version in 14 15 16; do
    echo "start containers (pg_version=$pg_version)."
    PG_VERSION=$pg_version docker compose -f $COMPOSE_FILE up --build -d

--- a/docs/rfcs/027-crash-consistent-layer-map-through-index-part.md
+++ b/docs/rfcs/027-crash-consistent-layer-map-through-index-part.md
@@ -0,0 +1,281 @@
+
+# Crash-Consistent Layer Map Updates By Leveraging `index_part.json`
+
+* Created on: Aug 23, 2023
+* Author: Christian Schwarz
+
+## Summary
+
+This RFC describes a simple scheme to make layer map updates crash consistent by leveraging the `index_part.json` in remote storage.
+Without such a mechanism, crashes can induce certain edge cases in which broadly held assumptions about system invariants don't hold.
+
+## Motivation
+
+### Background
+
+We can currently easily make complex, atomic updates to the layer map by means of an RwLock.
+If we crash or restart pageserver, we reconstruct the layer map from:
+1. local timeline directory contents
+2. remote `index_part.json` contents.
+
+The function that is responsible for this is called `Timeline::load_layer_map()`.
+The reconciliation process's behavior is the following:
+* local-only files will become part of the layer map as local-only layers and rescheduled for upload
+* For a file name that, by its name, is present locally and in the remote `index_part.json`, but where the local file has a different size (future: checksum) than the remote file, we will delete the local file and leave the remote file as a `RemoteLayer` in the layer map.
+
+### The Problem
+
+There are are cases where we need to make an atomic update to the layer map that involves **more than one layer**.
+The best example is compaction, where we need to insert the L1 layers generated from the L0 layers, and remove the L0 layers.
+As stated above, making the update to the layer map in atomic way is trivial.
+But, there is no system call API to make an atomic update to a directory that involves more than one file rename and deletion.
+Currently, we issue the system calls one by one and hope we don't crash.
+
+What happens if we crash and restart in the middle of that system call sequence?
+We will reconstruct the layer map according to the reconciliation process, taking as input whatever transitory state the timeline directory ended up in.
+
+We cannot roll back or complete the timeline directory update during which we crashed, because we keep no record of the changes we plan to make.
+
+### Problem's Implications For Compaction
+
+The implications of the above are primarily problematic for compaction.
+Specifically, the part of it that compacts L0 layers into L1 layers.
+
+Remember that compaction takes a set of L0 layers and reshuffles the delta records in them into L1 layer files.
+Once the L1 layer files are written to disk, it atomically removes the L0 layers from the layer map and adds the L1 layers to the layer map.
+It then deletes the L0 layers locally, and schedules an upload of the L1 layers and and updated index part.
+
+If we crash before deleting L0s, but after writing out L1s, the next compaction after restart will re-digest the L0s and produce new L1s.
+This means the compaction after restart will **overwrite** the previously written L1s.
+Currently we also schedule an S3 upload of the overwritten L1.
+
+If the compaction algorithm doesn't change between the two compaction runs, is deterministic, and uses the same set of L0s as input, then the second run will produce identical L1s and the overwrites will go unnoticed.
+
+*However*:
+1. the file size of the overwritten L1s may not be identical, and
+2. the bit pattern of the overwritten L1s may not be identical, and,
+3. in the future, we may want to make the compaction code non-determinstic, influenced by past access patterns, or otherwise change it, resulting in L1 overwrites with a different set of delta records than before the overwrite
+
+The items above are a problem for the [split-brain protection RFC](https://github.com/neondatabase/neon/pull/4919) because it assumes that layer files in S3 are only ever deleted, but never replaced (overPUTted).
+
+For example, if an unresponsive node A becomes active again after control plane has relocated the tenant to a new node B, the node A may overwrite some L1s.
+But node B based its world view on the version of node A's `index_part.json` from _before_ the overwrite.
+That earlier `index_part.json`` contained the file size of the pre-overwrite L1.
+If the overwritten L1 has a different file size, node B will refuse to read data from the overwritten L1.
+Effectively, the data in the L1 has become inaccessible to node B.
+If node B already uploaded an index part itself, all subsequent attachments will use node B's index part, and run into the same probem.
+
+If we ever introduce checksums instead of checking just the file size, then a mismatching bit pattern (2) will cause similar problems.
+
+In case of (1) and (2), where we know that the logical content of the layers is still the same, we can recover by manually patching the `index_part.json` of the new node to the overwritten L1's file size / checksum.
+
+But if (3) ever happens, the logical content may be different, and, we could have truly lost data.
+
+Given the above considerations, we should avoid making correctness of split-brain protection dependent on overwrites preserving _logical_ layer file contents.
+**It is a much cleaner separation of concerns to require that layer files are truly immutable in S3, i.e., PUT once and then only DELETEd, never overwritten (overPUTted).**
+
+## Design
+
+Instead of reconciling a layer map from local timeline directory contents and remote index part, this RFC proposes to view the remote index part as authoritative during timeline load.
+Local layer files will be recognized if they match what's listed in remote index part, and removed otherwise.
+
+During **timeline load**, the only thing that matters is the remote index part content.
+Essentially, timeline load becomes much like attach, except we don't need to prefix-list the remote timelines.
+The local timeline dir's `metadata` file does not matter.
+The layer files in the local timeline dir are seen as a nice-to-have cache of layer files that are in the remote index part.
+Any layer files in the local timeline dir that aren't in the remote index part are removed during startup.
+The `Timeline::load_layer_map()` no longer "merges" local timeline dir contents with the remote index part.
+Instead, it treats the remote index part as the authoritative layer map.
+If the local timeline dir contains a layer that is in the remote index part, that's nice, and we'll re-use it if file size (and in the future, check sum) match what's stated in the index part.
+If it doesn't match, we remove the file from the local timeline dir.
+
+After load, **at runtime**, nothing changes compared to what we did before this RFC.
+The procedure for single- and multi-object changes is reproduced here for reference:
+* For any new layers that the change adds:
+  * Write them to a temporary location.
+  * While holding layer map lock:
+    * Move them to the final location.
+    * Insert into layer map.
+* Make the S3 changes.
+  We won't reproduce the remote timeline client method calls here because these are subject to change.
+  Instead we reproduce the sequence of s3 changes that must result for a given single-/multi-object change:
+    * PUT layer files inserted by the change.
+    * PUT an index part that has insertions and deletions of the change.
+    * DELETE the layer files that are deleted by the change.
+
+Note that it is safe for the DELETE to be deferred arbitrarily.
+* If it never happens, we leak the object, but, that's not a correctness concern.
+* As of #4938, we don't schedule the remote timeline client operation for deletion immediately, but, only when we drop the `LayerInner`.
+* With the [split-brain protection RFC](https://github.com/neondatabase/neon/pull/4919), the deletions will be written to deletion queue for processing when it's safe to do so (see the RFC for details).
+
+## How This Solves The Problem
+
+If we crash before we've finished the S3 changes, then timeline load will reset layer map to the state that's in the S3 index part.
+The S3 change sequence above is obviously crash-consistent.
+If we crash before the index part PUT, then we leak the inserted layer files to S3.
+If we crash after the index part PUT, we leak the to-be-DELETEd layer files to S3.
+Leaking is fine, it's a pre-existing condition and not addressed in this RFC.
+
+Multi-object changes that previously created and removed files in timeline dir are now atomic because the layer map updates are atomic and crash consistent:
+* atomic layer map update at runtime, currently by using an RwLock in write mode
+* atomic `index_part.json` update in S3, as per guarantee that S3 PUT is atomic
+* local timeline dir state:
+  * irrelevant for layer map content => irrelevant for atomic updates / crash consistency
+  * if we crash after index part PUT, local layer files will be used, so, no on-demand downloads neede for them
+  * if we crash before index part PUT, local layer files will be deleted
+
+## Trade-Offs
+
+### Fundamental
+
+If we crash before finishing the index part PUT, we lose all the work that hasn't reached the S3 `index_part.json`:
+* wal ingest: we lose not-yet-uploaded L0s; load on the **safekeepers** + work for pageserver
+* compaction: we lose the entire compaction iteration work; need to re-do it again
+* gc: no change to what we have today
+
+If the work is still deemed necessary after restart, the restarted restarted pageserver will re-do this work.
+The amount of work to be re-do is capped to the lag of S3 changes to the local changes.
+Assuming upload queue allows for unlimited queue depth (that's what it does today), this means:
+* on-demand downloads that were needed to do the work: are likely still present, not lost
+* wal ingest: currently unbounded
+* L0 => L1 compaction: CPU time proportional to `O(sum(L0 size))` and upload work proportional to `O()`
+  * Compaction threshold is 10 L0s and each L0 can be up to 256M in size. Target size for L1 is 128M.
+  * In practive, most L0s are tiny due to 10minute `DEFAULT_CHECKPOINT_TIMEOUT`.
+* image layer generation: CPU time `O(sum(input data))` + upload work `O(sum(new image layer size))`
+  * I have no intuition how expensive / long-running it is in reality.
+* gc: `update_gc_info`` work (not substantial, AFAIK)
+
+To limit the amount of lost upload work, and ingest work, we can limit the upload queue depth (see suggestions in the next sub-section).
+However, to limit the amount of lost CPU work, we would need a way to make make the compaction/image-layer-generation algorithms interruptible & resumable.
+We aren't there yet, the need for it is tracked by ([#4580](https://github.com/neondatabase/neon/issues/4580)).
+However, this RFC is not constraining the design space either.
+
+### Practical
+
+#### Pageserver Restarts
+
+Pageserver crashes are very rare ; it would likely be acceptable to re-do the lost work in that case.
+However, regular pageserver restart happen frequently, e.g., during weekly deploys.
+
+In general, pageserver restart faces the problem of tenants that "take too long" to shut down.
+They are a problem because other tenants that shut down quickly are unavailble while we wait for the slow tenants to shut down.
+We currently allot 10 seconds for graceful shutdown until we SIGKILL the pageserver process (as per `pageserver.service` unit file).
+A longer budget would expose tenants that are done early to a longer downtime.
+A short budget would risk throwing away more work that'd have to be re-done after restart.
+
+In the context of this RFC, killing the process would mean losing the work that hasn't made it to S3.
+We can mitigate this problem as follows:
+0. initially, by accepting that we need to do the work again
+1. short-term, introducing measures to cap the amount of in-flight work:
+
+   - cap upload queue length, use backpressure to slow down compaction
+   - disabling compaction/image-layer-generation X minutes before `systemctl restart pageserver`
+   - introducing a read-only shutdown state for tenants that are fast to shut down;
+     that state would be equivalent to the state of a tenant in hot standby / readonly mode.
+
+2. mid term, by not restarting pageserver in place, but using [*seamless tenant migration*](https://github.com/neondatabase/neon/pull/5029) to drain a pageserver's tenants before we restart it.
+
+#### `disk_consistent_lsn` can go backwards
+
+`disk_consistent_lsn` can go backwards across restarts if we crash before we've finished the index part PUT.
+Nobody should care about it, because the only thing that matters is `remote_consistent_lsn`.
+Compute certainly doesn't care about `disk_consistent_lsn`.
+
+
+## Side-Effects Of This Design
+
+* local `metadata` is basically reduced to a cache of which timelines exist for this tenant; i.e., we can avoid a `ListObjects` requests for a tenant's timelines during tenant load.
+
+## Limitations
+
+Multi-object changes that span multiple timelines aren't covered by this RFC.
+That's fine because we currently don't need them, as evidenced by the absence
+of a Pageserver operation that holds multiple timelines' layer map lock at a time.
+
+## Impacted components
+
+Primarily pageservers.
+
+Safekeepers will experience more load when we need to re-ingest WAL because we've thrown away work.
+No changes to safekeepers are needed.
+
+## Alternatives considered
+
+### Alternative 1: WAL
+
+We could have a local WAL for timeline dir changes, as proposed here https://github.com/neondatabase/neon/issues/4418 and partially implemented here https://github.com/neondatabase/neon/pull/4422 .
+The WAL would be used to
+1. make multi-object changes atomic
+2. replace `reconcile_with_remote()` reconciliation: scheduling of layer upload would be part of WAL replay.
+
+The WAL is appealing in a local-first world, but, it's much more complex than the design described above:
+* New on-disk state to get right.
+* Forward- and backward-compatibility development costs in the future.
+
+### Alternative 2: Flow Everything Through `index_part.json`
+
+We could have gone to the other extreme and **only** update the layer map whenever we've PUT `index_part.json`.
+I.e., layer map would always be the last-persisted S3 state.
+That's axiomatically beautiful, not least because it fully separates the layer file production and consumption path (=> [layer file spreading proposal](https://www.notion.so/neondatabase/One-Pager-Layer-File-Spreading-Christian-eb6b64182a214e11b3fceceee688d843?pvs=4)).
+And it might make hot standbys / read-only pageservers less of a special case in the future.
+
+But, I have some uncertainties with regard to WAL ingestion, because it needs to be able to do some reads for the logical size feedback to safekeepers.
+
+And it's silly that we wouldn't be able to use the results of compaction or image layer generation before we're done with the upload.
+
+Lastly, a temporarily clogged-up upload queue (e.g. S3 is down) shouldn't immediately render ingestion unavailable.
+
+### Alternative 3: Sequence Numbers For Layers
+
+Instead of what's proposed in this RFC, we could use unique numbers to identify layer files:
+
+```
+# before
+tenants/$tenant/timelines/$timeline/$key_and_lsn_range
+# after
+tenants/$tenant/timelines/$timeline/$layer_file_id-$key_and_lsn_range
+```
+
+To guarantee uniqueness, the unqiue number is a sequence number, stored in `index_part.json`.
+
+This alternative does not solve atomic layer map updates.
+In our crash-during-compaction scenario above, the compaction run after the crash will not overwrite the L1s, but write/PUT new files with new sequence numbers.
+In fact, this alternative makes it worse because the data is now duplicated in the not-overwritten and overwritten L1 layer files.
+We'd need to write a deduplication pass that checks if perfectly overlapping layers have identical contents.
+
+However, this alternative is appealing because it systematically prevents overwrites at a lower level than this RFC.
+
+So, this alternative is sufficient for the needs of the split-brain safety RFC (immutable layer files locally and in S3).
+But it doesn't solve the problems with crash-during-compaction outlined earlier in this RFC, and in fact, makes it much more accute.
+The proposed design in this RFC addresses both.
+
+So, if this alternative sounds appealing, we should implement the proposal in this RFC first, then implement this alternative on top.
+That way, we avoid a phase where the crash-during-compaction problem is accute.
+
+## Related issues
+
+- https://github.com/neondatabase/neon/issues/4749
+- https://github.com/neondatabase/neon/issues/4418
+  - https://github.com/neondatabase/neon/pull/4422
+- https://github.com/neondatabase/neon/issues/5077
+- https://github.com/neondatabase/neon/issues/4088
+  - (re)resolutions:
+    - https://github.com/neondatabase/neon/pull/4696
+    - https://github.com/neondatabase/neon/pull/4094
+      - https://neondb.slack.com/archives/C033QLM5P7D/p1682519017949719
+
+Note that the test case introduced in https://github.com/neondatabase/neon/pull/4696/files#diff-13114949d1deb49ae394405d4c49558adad91150ba8a34004133653a8a5aeb76 will produce L1s with the same logical content, but, as outlined in the last paragraph of the _Problem Statement_ section above, we don't want to make that  assumption in order to fix the problem.
+
+
+## Implementation Plan
+
+1. Remove support for `remote_storage=None`, because we now rely on the existence of an index part.
+
+    - The nasty part here is to fix all the tests that fiddle with the local timeline directory.
+      Possibly they are just irrelevant with this change, but, each case will require inspection.
+
+2. Implement the design above.
+
+    - Initially, ship without the mitigations for restart and accept we will do some work twice.
+    - Measure the impact and implement one of the mitigations.
+
--- a/docs/rfcs/028-pageserver-migration.md
+++ b/docs/rfcs/028-pageserver-migration.md
@@ -0,0 +1,599 @@
+# Seamless tenant migration
+
+- Author: john@neon.tech
+- Created on 2023-08-11
+- Implemented on ..
+
+## Summary
+
+The preceding [generation numbers RFC](025-generation-numbers.md) may be thought of as "making tenant
+migration safe". Following that,
+this RFC is about how those migrations are to be done:
+
+1. Seamlessly (without interruption to client availability)
+2. Quickly (enabling faster operations)
+3. Efficiently (minimizing I/O and $ cost)
+
+These points are in priority order: if we have to sacrifice
+efficiency to make a migration seamless for clients, we will
+do so, etc.
+
+This is accomplished by introducing two high level changes:
+
+- A dual-attached state for tenants, used in a control-plane-orchestrated
+  migration procedure that preserves availability during a migration.
+- Warm secondary locations for tenants, where on-disk content is primed
+  for a fast migration of the tenant from its current attachment to this
+  secondary location.
+
+## Motivation
+
+Migrating tenants between pageservers is essential to operating a service
+at scale, in several contexts:
+
+1. Responding to a pageserver node failure by migrating tenants to other pageservers
+2. Balancing load and capacity across pageservers, for example when a user expands their
+   database and they need to migrate to a pageserver with more capacity.
+3. Restarting pageservers for upgrades and maintenance
+
+The current situation steps for migration are:
+
+- detach from old node; skip if old node is dead; (the [skip part is still WIP](https://github.com/neondatabase/cloud/issues/5426)).
+- attach to new node
+- re-configure endpoints to use the new node
+
+Once [generation numbers](025-generation-numbers.md) are implemented,
+the detach step is no longer critical for correctness. So, we can
+
+- attach to a new node,
+- re-configure endpoints to use the new node, and then
+- detach from the old node.
+
+However, this still does not meet our seamless/fast/efficient goals:
+
+- Not fast: The new node will have to download potentially large amounts
+  of data from S3, which may take many minutes.
+- Not seamless: If we attach to a new pageserver before detaching an old one,
+  the new one might delete some objects that interrupt availability of reads on the old one.
+- Not efficient: the old pageserver will continue uploading
+  S3 content during the migration that will never be read.
+
+The user expectations for availability are:
+
+- For planned maintenance, there should be zero availability
+  gap. This expectation is fulfilled by this RFC.
+- For unplanned changes (e.g. node failures), there should be
+  minimal availability gap. This RFC provides the _mechanism_
+  to fail over quickly, but does not provide the failure _detection_
+  nor failover _policy_.
+
+## Non Goals
+
+- Defining service tiers with different storage strategies: the same
+  level of HA & overhead will apply to all tenants. This doesn't rule out
+  adding such tiers in future.
+- Enabling pageserver failover in the absence of a control plane: the control
+  plane will remain the source of truth for what should be attached where.
+- Totally avoiding availability gaps on unplanned migrations during
+  a failure (we expect a small, bounded window of
+  read unavailability of very recent LSNs)
+- Workload balancing: this RFC defines the mechanism for moving tenants
+  around, not the higher level logic for deciding who goes where.
+- Defining all possible configuration flows for tenants: the migration process
+  defined in this RFC demonstrates the sufficiency of the pageserver API, but
+  is not the only kind of configuration change the control plane will ever do.
+  The APIs defined here should let the control plane move tenants around in
+  whatever way is needed while preserving data safety and read availability.
+
+## Impacted components
+
+Pageserver, control plane
+
+## Terminology
+
+- **Attachment**: a tenant is _attached_ to a pageserver if it has
+  been issued a generation number, and is running an instance of
+  the `Tenant` type, ingesting the WAL, and available to serve
+  page reads.
+- **Location**: locations are a superset of attachments. A location
+  is a combination of a tenant and a pageserver. We may _attach_ at a _location_.
+
+- **Secondary location**: a location which is not currently attached.
+- **Warm secondary location**: a location which is not currently attached, but is endeavoring to maintain a warm local cache of layers. We avoid calling this a _warm standby_ to avoid confusion with similar postgres features.
+
+## Implementation (high level)
+
+### Warm secondary locations
+
+To enable faster migrations, we will identify at least one _secondary location_
+for each tenant. This secondary location will keep a warm cache of layers
+for the tenant, so that if it is later attached, it can catch up with the
+latest LSN quickly: rather than downloading everything, it only has to replay
+the recent part of the WAL to advance from the remote_consistent_offset to the
+most recent LSN in the WAL.
+
+The control plane is responsible for selecting secondary locations, and
+calling into pageservers to configure tenants into a secondary mode at this
+new location, as well as attaching the tenant in its existing primary location.
+
+The attached pageserver for a tenant will publish a [layer heatmap](#layer-heatmap)
+to advise secondaries of which layers should be downloaded.
+
+### Location modes
+
+Currently, we consider a tenant to be in one of two states on a pageserver:
+
+- Attached: active `Tenant` object, and layers on local disk
+- Detached: no layers on local disk, no runtime state.
+
+We will extend this with finer-grained modes, whose purpose will become
+clear in later sections:
+
+- **AttachedSingle**: equivalent the existing attached state.
+- **AttachedMulti**: like AttachedSingle, holds an up to date generation, but
+  does not do deletions.
+- **AttachedStale**: like AttachedSingle, holds a stale generation,
+  do not do any remote storage operations.
+- **Secondary**: keep local state on disk, periodically update from S3.
+- **Detached**: equivalent to existing detached state.
+
+To control these finer grained states, a new pageserver API endpoint will be added.
+
+### Cutover procedure
+
+Define old location and new location as "Node A" and "Node B". Consider
+the case where both nodes are available, and Node B was previously configured
+as a secondary location for the tenant we are migrating.
+
+The cutover procedure is orchestrated by the control plane, calling into
+the pageservers' APIs:
+
+1. Call to Node A requesting it to flush to S3 and enter AttachedStale state
+2. Increment generation, and call to Node B requesting it to enter AttachedMulti
+   state with the new generation.
+3. Call to Node B, requesting it to download the latest hot layers from remote storage,
+   according to the latest heatmap flushed by Node A.
+4. Wait for Node B's WAL ingestion to catch up with node A's
+5. Update endpoints to use node B instead of node A
+6. Call to node B requesting it to enter state AttachedSingle.
+7. Call to node A requesting it to enter state Secondary
+
+The following table summarizes how the state of the system advances:
+
+|     Step      |     Node A     |     Node B     | Node used by endpoints |
+| :-----------: | :------------: | :------------: | :--------------------: |
+| 1 (_initial_) | AttachedSingle |   Secondary    |           A            |
+|       2       | AttachedStale  | AttachedMulti  |           A            |
+|       3       | AttachedStale  | AttachedMulti  |           A            |
+|       4       | AttachedStale  | AttachedMulti  |           A            |
+| 5 (_cutover_) | AttachedStale  | AttachedMulti  |           B            |
+|       6       | AttachedStale  | AttachedSingle |           B            |
+|  7 (_final_)  |   Secondary    | AttachedSingle |           B            |
+
+The procedure described for a clean handover from a live node to a secondary
+is also used for failure cases and for migrations to a location that is not
+configured as a secondary, by simply skipping irrelevant steps, as described in
+the following sections.
+
+#### Migration from an unresponsive node
+
+If node A is unavailable, then all calls into
+node A are skipped and we don't wait for B to catch up before
+switching updating the endpoints to use B.
+
+#### Migration to a location that is not a secondary
+
+If node B is initially in Detached state, the procedure is identical. Since Node B
+is coming from a Detached state rather than Secondary, the download of layers and
+catch up with WAL will take much longer.
+
+We might do this if:
+
+- Attached and secondary locations are both critically low on disk, and we need
+  to migrate to a third node with more resources available.
+- We are migrating a tenant which does not use secondary locations to save on cost.
+
+#### Permanent migration away from a node
+
+In the final step of the migration, we generally request the original node to enter a Secondary
+state. This is typical if we are doing a planned migration during maintenance, or to
+balance CPU/network load away from a node.
+
+One might also want to permanently migrate away: this can be done by simply removing the secondary
+location after the migration is complete, or as an optimization by substituting the Detached state
+for the Secondary state in the final step.
+
+#### Cutover diagram
+
+```mermaid
+sequenceDiagram
+participant CP as Control plane
+participant A as Node A
+participant B as Node B
+participant E as Endpoint
+
+CP->>A: PUT Flush & go to AttachedStale
+note right of A: A continues to ingest WAL
+CP->>B: PUT AttachedMulti
+CP->>B: PUT Download layers from latest heatmap
+note right of B: B downloads from S3
+loop Poll until download complete
+CP->>B: GET download status
+end
+activate B
+note right of B: B ingests WAL
+loop Poll until catch up
+CP->>B: GET visible WAL
+CP->>A: GET visible WAL
+end
+deactivate B
+CP->>E: Configure to use Node B
+E->>B: Connect for reads
+CP->>B: PUT AttachedSingle
+CP->>A: PUT Secondary
+```
+
+#### Cutover from an unavailable pageserver
+
+This case is far simpler: we may skip straight to our intended
+end state.
+
+```mermaid
+sequenceDiagram
+participant A as Node A
+participant CP as Control plane
+participant B as Node B
+participant E as Endpoint
+
+note right of A: Node A offline
+activate A
+CP->>B: PUT AttachedSingle
+CP->>E: Configure to use Node B
+E->>B: Connect for reads
+deactivate A
+```
+
+## Implementation (detail)
+
+### Purpose of AttachedMulti, AttachedStale
+
+#### AttachedMulti
+
+Ordinarily, an attached pageserver whose generation is the latest may delete
+layers at will (e.g. during compaction). If a previous generation pageserver
+is also still attached, and in use by endpoints, then this layer deletion could
+lead to a loss of availability for the endpoint when reading from the previous
+generation pageserver.
+
+The _AttachedMulti_ state simply disables deletions. These will be enqueued
+in `RemoteTimelineClient` until the control plane transitions the
+node into AttachedSingle, which unblocks deletions.  Other remote storage operations
+such as uploads are not blocked.
+
+AttachedMulti is not required for data safety, only to preserve availability
+on pageservers running with stale generations.
+
+A node enters AttachedMulti only when explicitly asked to by the control plane. It should
+only remain in this state for the duration of a migration.
+
+If a control plane bug leaves
+the node in AttachedMulti for a long time, then we must avoid unbounded memory use from enqueued
+deletions. This may be accomplished simply, by dropping enqueued deletions when some modest
+threshold of delayed deletions (e.g. 10k layers per tenant) is reached. As with all deletions,
+it is safe to skip them, and the leaked objects will be eventually cleaned up by scrub or
+by timeline deletion.
+
+During AttachedMulti, the Tenant is free to drop layers from local disk in response to
+disk pressure: only the deletion of remote layers is blocked.
+
+#### AttachedStale
+
+Currently, a pageserver with a stale generation number will continue to
+upload layers, but be prevented from completing deletions. This is safe, but inefficient: layers uploaded by this stale generation
+will not be read back by future generations of pageservers.
+
+The _AttachedStale_ state disables S3 uploads. The stale pageserver
+will continue to ingest the WAL and write layers to local disk, but not to
+do any uploads to S3.
+
+A node may enter AttachedStale in two ways:
+
+- Explicitly, when control plane calls into the node at the start of a migration.
+- Implicitly, when the node tries to validate some deletions and discovers
+  that its generation is stale.
+
+The AttachedStale state also disables sending consumption metrics from
+that location: it is interpreted as an indication that some other pageserver
+is already attached or is about to be attached, and that new pageserver will
+be responsible for sending consumption metrics.
+
+#### Disk Pressure & AttachedStale
+
+Over long periods of time, a tenant location in AttachedStale will accumulate data
+on local disk, as it cannot evict any layers written since it entered the
+AttachStale state. We rely on the control plane to revert the location to
+Secondary or Detached at the end of a migration.
+
+This scenario is particularly noteworthy when evacuating all tenants on a pageserver:
+since _all_ the attached tenants will go into AttachedStale, we will be doing no
+uploads at all, therefore ingested data will cause disk usage to increase continuously.
+Under nominal conditions, the available disk space on pageservers should be sufficient
+to complete the evacuation before this becomes a problem, but we must also handle
+the case where we hit a low disk situation while in this state.
+
+The concept of disk pressure already exists in the pageserver: the `disk_usage_eviction_task`
+touches each Tenant when it determines that a low-disk condition requires
+some layer eviction. Having selected layers for eviction, the eviction
+task calls `Timeline::evict_layers`.
+
+**Safety**: If evict_layers is called while in AttachedStale state, and some of the to-be-evicted
+layers are not yet uploaded to S3, then the block on uploads will be lifted. This
+will result in leaking some objects once a migration is complete, but will enable
+the node to manage its disk space properly: if a node is left with some tenants
+in AttachedStale indefinitely due to a network partition or control plane bug,
+these tenants will not cause a full disk condition.
+
+### Warm secondary updates
+
+#### Layer heatmap
+
+The secondary location's job is to serve reads **with the same quality of service as the original location
+was serving them around the time of a migration**. This does not mean the secondary
+location needs the whole set of layers: inactive layers that might soon
+be evicted on the attached pageserver need not be downloaded by the
+secondary. A totally idle tenant only needs to maintain enough on-disk
+state to enable a fast cold start (i.e. the most recent image layers are
+typically sufficient).
+
+To enable this, we introduce the concept of a _layer heatmap_, which
+acts as an advisory input to secondary locations to decide which
+layers to download from S3.
+
+#### Attached pageserver
+
+The attached pageserver, if in state AttachedSingle, periodically
+uploads a serialized heat map to S3. It may skip this if there
+is no change since the last time it uploaded (e.g. if the tenant
+is totally idle).
+
+Additionally, when the tenant is flushed to remote storage prior to a migration
+(the first step in [cutover procedure](#cutover-procedure)), 
+the heatmap is written out. This enables a future attached pageserver
+to get an up to date view when deciding which layers to download.
+
+#### Secondary location behavior
+
+Secondary warm locations run a simple loop, implemented separately from
+the main `Tenant` type, which represents attached tenants:
+
+- Download the layer heatmap
+- Select any "hot enough" layers to download, if there is sufficient
+  free disk space.
+- Download layers, if they were not previously evicted (see below)
+- Download the latest index_part.json
+- Check if any layers currently on disk are no longer referenced by
+  IndexPart & delete them
+
+Note that the heatmap is only advisory: if a secondary location has plenty
+of disk space, it may choose to retain layers that aren't referenced
+by the heatmap, as long as they are still referenced by the IndexPart. Conversely,
+if a node is very low on disk space, it might opt to raise the heat threshold required
+to both downloading a layer, until more disk space is available.
+
+#### Secondary locations & disk pressure
+
+Secondary locations are subject to eviction on disk pressure, just as
+attached locations are.  For eviction purposes, the access time of a
+layer in a secondary location will be the access time given in the heatmap,
+rather than the literal time at which the local layer file was accessed.
+
+The heatmap will indicate which layers are in local storage on the attached
+location.  The secondary will always attempt to get back to having that
+set of layers on disk, but to avoid flapping, it will remember the access
+time of the layer it was most recently asked to evict, and layers whose
+access time is below that will not be re-downloaded.
+
+The resulting behavior is that after a layer is evicted from a secondary
+location, it is only re-downloaded once the attached pageserver accesses
+the layer and uploads a heatmap reflecting that access time.  On a pageserver
+restart, the secondary location will attempt to download all layers in
+the heatmap again, if they are not on local disk.
+
+This behavior will be slightly different when secondary locations are
+used for "low energy tenants", but that is beyond the scope of this RFC.
+
+### Location configuration API
+
+Currently, the `/tenant/<tenant_id>/config` API defines various
+tunables like compaction settings, which apply to the tenant irrespective
+of which pageserver it is running on.
+
+A new "location config" structure will be introduced, which defines
+configuration which is per-tenant, but local to a particular pageserver,
+such as the attachment mode and whether it is a secondary.
+
+The pageserver will expose a new per-tenant API for setting
+the state: `/tenant/<tenant_id>/location/config`.
+
+Body content:
+
+```
+{
+  state: 'enum{Detached, Secondary, AttachedSingle, AttachedMulti, AttachedStale}',
+  generation: Option<u32>,
+  configuration: `Option<TenantConfig>`
+  flush: bool
+}
+```
+
+Existing `/attach` and `/detach` endpoint will have the same
+behavior as calling `/location/config` with `AttachedSingle` and `Detached`
+states respectively. These endpoints will be deprecated and later
+removed.
+
+The generation attribute is mandatory for entering `AttachedSingle` or
+`AttachedMulti`.
+
+The configuration attribute is mandatory when entering any state other
+than `Detached`. This configuration is the same as the body for
+the existing `/tenant/<tenant_id>/config` endpoint.
+
+The `flush` argument indicates whether the pageservers should flush
+to S3 before proceeding: this only has any effect if the node is
+currently in AttachedSingle or AttachedMulti. This is used
+during the first phase of migration, when transitioning the
+old pageserver to AttachedSingle.
+
+The `/re-attach` API response will be extended to include a `state` as
+well as a `generation`, enabling the pageserver to enter the
+correct state for each tenant on startup.
+
+### Database schema for locations
+
+A new table `ProjectLocation`:
+
+- pageserver_id: int
+- tenant_id: TenantId
+- generation: Option<int>
+- state: `enum(Secondary, AttachedSingle, AttachedMulti)`
+
+Notes:
+
+- It is legacy for a Project to have zero `ProjectLocation`s
+- The `pageserver` column in `Project` now means "to which pageserver should
+  endpoints connect", rather than simply which pageserver is attached.
+- The `generation` column in `Project` remains, and is incremented and used
+  to set the generation of `ProjectLocation` rows when they are set into
+  an attached state.
+- The `Detached` state is implicitly represented as the absence of
+  a `ProjectLocation`.
+
+### Executing migrations
+
+Migrations will be implemented as Go functions, within the
+existing `Operation` framework in the control plane. These
+operations are persistent, such that they will always keep
+trying until completion: this property is important to avoid
+leaving garbage behind on pageservers, such as AttachedStale
+locations.
+
+### Recovery from failures during migration
+
+During migration, the control plane may encounter failures of either
+the original or new pageserver, or both:
+
+- If the original fails, skip past waiting for the new pageserver
+  to catch up, and put it into AttachedSingle immediately.
+- If the new node fails, put the old pageserver into Secondary
+  and then back into AttachedSingle (this has the effect of
+  retaining on-disk state and granting it a fresh generation number).
+- If both nodes fail, keep trying until one of them is available
+  again.
+
+### Control plane -> Pageserver reconciliation
+
+A migration may be done while the old node is unavailable,
+in which case the old node may still be running in an AttachedStale
+state.
+
+In this case, it is undesirable to have the migration `Operation`
+stay alive until the old node eventually comes back online
+and can be cleaned up. To handle this, the control plane
+should run a background reconciliation process to compare
+a pageserver's attachments with the database, and clean up
+any that shouldn't be there any more.
+
+Note that there will be no work to do if the old node was really
+offline, as during startup it will call into `/re-attach` and
+be updated that way. The reconciliation will only be needed
+if the node was unavailable but still running.
+
+## Alternatives considered
+
+### Only enabling secondary locations for tenants on a higher service tier
+
+This will make sense in future, especially for tiny databases that may be
+downloaded from S3 in milliseconds when needed.
+
+However, it is not wise to do it immediately, because pageservers contain
+a mixture of higher and lower tier workloads. If we had 1 tenant with
+a secondary location and 9 without, then those other 9 tenants will do
+a lot of I/O as they try to recover from S3, which may degrade the
+service of the tenant which had a secondary location.
+
+Until we segregate tenant on different service tiers on different pageserver
+nodes, or implement & test QoS to ensure that tenants with secondaries are
+not harmed by tenants without, we should use the same failover approach
+for all the tenants.
+
+### Hot secondary locations (continuous WAL replay)
+
+Instead of secondary locations populating their caches from S3, we could
+have them consume the WAL from safekeepers. The downsides of this would be:
+
+- Double load on safekeepers, which are a less scalable service than S3
+- Secondary locations' on-disk state would end up subtly different to
+  the remote state, which would make synchronizing with S3 more complex/expensive
+  when going into attached state.
+
+The downside of only updating secondary locations from S3 is that we will
+have a delay during migration from replaying the LSN range between what's
+in S3 and what's in the pageserver. This range will be very small on
+planned migrations, as we have the old pageserver flush to S3 immediately
+before attaching the new pageserver. On unplanned migrations (old pageserver
+is unavailable), the range of LSNs to replay is bounded by the flush frequency
+on the old pageserver. However, the migration doesn't have to wait for the
+replay: it's just that not-yet-replayed LSNs will be unavailable for read
+until the new pageserver catches up.
+
+We expect that pageserver reads of the most recent LSNs will be relatively
+rare, as for an active endpoint those pages will usually still be in the postgres
+page cache: this leads us to prefer synchronizing from S3 on secondary
+locations, rather than consuming the WAL from safekeepers.
+
+### Cold secondary locations
+
+It is not functionally necessary to keep warm caches on secondary locations at all. However, if we do not, then
+we would experience a de-facto availability loss in unplanned migrations, as reads to the new node would take an extremely long time (many seconds, perhaps minutes).
+
+Warm caches on secondary locations are necessary to meet
+our availability goals.
+
+### Pageserver-granularity failover
+
+Instead of migrating tenants individually, we could have entire spare nodes,
+and on a node death, move all its work to one of these spares.
+
+This approach is avoided for several reasons:
+
+- we would still need fine-grained tenant migration for other
+  purposes such as balancing load
+- by sharing the spare capacity over many peers rather than one spare node,
+  these peers may use the capacity for other purposes, until it is needed
+  to handle migrated tenants. e.g. for keeping a deeper cache of their
+  attached tenants.
+
+### Readonly during migration
+
+We could simplify migrations by making both previous and new nodes go into a
+readonly state, then flush remote content from the previous node, then activate
+attachment on the secondary node.
+
+The downside to this approach is a potentially large gap in readability of
+recent LSNs while loading data onto the new node. To avoid this, it is worthwhile
+to incur the extra cost of double-replaying the WAL onto old and new nodes' local
+storage during a migration.
+
+### Peer-to-peer pageserver communication
+
+Rather than uploading the heatmap to S3, attached pageservers could make it
+available to peers.
+
+Currently, pageservers have no peer to peer communication, so adding this
+for heatmaps would incur significant overhead in deployment and configuration
+of the service, and ensuring that when a new pageserver is deployed, other
+pageservers are updated to be aware of it.
+
+As well as simplifying implementation, putting heatmaps in S3 will be useful
+for future analytics purposes -- gathering aggregated statistics on activity
+pattersn across many tenants may be done directly from data in S3.
--- a/docs/rfcs/029-sharding-phase1.md
+++ b/docs/rfcs/029-sharding-phase1.md
@@ -0,0 +1,244 @@
+# Sharding Phase 1: Static Key-space Sharding
+
+## Summary
+
+To enable databases with sizes approaching the capacity of a pageserver's disk,
+it is necessary to break up the storage for the database, or _shard_ it.
+
+Sharding in general is a complex area.  This RFC aims to define a modest initial
+capability that will permit creating large-capacity databases using a static configuration
+defined at time of Tenant creation.
+
+## Motivation
+
+Currently, all data for a Tenant, including all its timelines, is stored on a single
+pageserver.  The local storage required may be several times larger than the actual
+database size, due to LSM write inflation.
+
+If a database is larger than what one pageserver can hold, then it becomes impossible
+for the pageserver to hold it in local storage, as it must do to provide service to
+clients.
+
+### Prior art
+
+Numerous: sharding is a long-discussed feature for the pageserver.
+
+Prior art in other distributed systems is too broad to capture here: pretty much
+any scale out storage system does something like this.
+
+## Requirements
+
+- Enable creating a large (for example, 16TiB) database without requiring dedicated
+  pageserver nodes.
+- Share read/write bandwidth costs for large databases across pageservers, as well
+  as storage capacity, in order to avoid large capacity databases acting as I/O hotspots
+  that disrupt service to other tenants.
+- Our data distribution scheme should handle sparse/nonuniform keys well, since postgres
+  does not write out a single contiguous ranges of page numbers.
+
+*Note: the definition of 'large database' is arbitrary, but the lower bound is to ensure that a database
+that a user might create on a current-gen enterprise SSD should also work well on
+Neon.  The upper bound is whatever postgres can handle: i.e. we must make sure that the
+pageserver backend is not the limiting factor in the database size*.
+
+## Non Goals
+
+- Independently distributing timelines within the same tenant.  If a tenant has many
+  timelines, then sharding may be a less efficient mechanism for distributing load than
+  sharing out timelines between pageservers.
+- Distributing work in the LSN dimension: this RFC focuses on the Key dimension only,
+  based on the idea that separate mechanisms will make sense for each dimension.
+
+## Impacted Components
+
+pageserver, control plane, safekeeper (optional)
+
+## Terminology
+
+**Key**: a postgres page number.  In the sense that the pageserver is a versioned key-value store,
+the page number is the key in that store.
+
+**LSN dimension**: this just means the range of LSNs (history), when talking about the range
+of keys and LSNs as a two dimensional space.
+
+## Implementation
+
+### Key sharding vs. LSN sharding
+
+When we think of sharding across the two dimensional key/lsn space, this is an
+opportunity to think about how the two dimensions differ:
+- Sharding the key space distributes the _write_ workload of ingesting data
+  and compacting.  This work must be carefully managed so that exactly one
+  node owns a given key.
+- Sharding the LSN space distributes the _historical read_ workload.  This work
+  can be done by anyone without any special coordination, as long as they can
+  see the remote index and layers.
+
+The key sharding is the harder part, and also the more urgent one, to support larger
+capacity databases.  Because distributing historical LSN read work is a relatively
+simpler problem that most users don't have, we defer it to future work.  It is anticipated
+that some quite simple P2P offload model will enable distributing work for historical
+reads: a node which is low on space can call out to peer to ask it to download and
+serve reads from a historical layer.
+
+### Key mapping scheme
+
+Having decided to focus on key sharding, we must next decide how we will map
+keys to shards.
+
+It is proposed to use a "wide striping" approach, to obtain a good compromise
+between data locality and avoiding entire large relations mapping to the same shard.
+
+The mapping is quite simple:
+- Define a stripe size, such as 256MiB.  Map this to a key count, such that a contiguous
+  range of 256MiB keys would all fall into this stripe, i.e. divide by 8kiB to get 32k.
+- Map a key to a stripe by integer division.
+- Map a stripe to a shard by taking the shard index modulo the shard count.
+
+This scheme will achieve a good balance as long as there is no aliasing of the keys
+to the stripe width.  In the example above, if someone had 4 shards and wrote
+keys that were all 4*32k apart, they would all map to the same shard.  However, we do
+not have to worry about this, since end users do not control page numbers: as long as
+we do not pick stripe sizes that map to any problematic postgres behaviors, we'll be fine.
+
+### Important Types
+
+#### `ShardMap`
+
+Provides all the information needed to route a request for a particular
+key to the correct pageserver:
+- Stripe size
+- Shard count
+- Address of the pageserver hosting each shard
+
+This structure's size is linear with the number of shards.
+
+#### `ShardIdentity`
+
+Provides the information needed to know whether a particular key belongs
+to a particular shard:
+- Stripe size
+- Shard count
+- Shard index
+
+This structure's size is constant.
+
+### Pageserver changes
+
+Everywhere the Pageserver currently deals with Tenants, it will move to dealing with
+TenantShards, which are just a `Tenant` plus a `ShardIdentity` telling it which part
+of the keyspace it owns.
+
+When the pageserver subscribes to a safekeeper for WAL updates, it must provide
+its `ShardIdentity` to receive the relevant subset of the WAL.
+
+When the pageserver writes layers and index_part.json to remote storage, it must
+include the shard index & count in the name, to avoid collisions (the count is
+necessary for future-proofing: the count will vary in time).  These keys
+will also include a generation number: the [generation numbers](025-generation-numbers.md) system will work
+exactly the same for TenantShards as it does for Tenants today: each shard will have
+its own generation number.
+
+The pageserver doesn't have to do anything special during ingestion, compaction
+or GC.  It is implicitly operating on the subset of keys that map to its ShardIdentity.
+This will result in sparse layer files, containing keys only in the stripes that this
+shard owns.  Where optimizations currently exist in compaction for spotting "gaps" in
+the key range, these should be updated to ignore gaps that are due to sharding, to
+avoid spuriously splitting up layers ito stripe-sized pieces.
+
+### Pageserver Controller changes
+
+The pageserver controller is a new component, which is responsible for abstracting
+away the business of managing individual tenant placement on pagservers.  It will
+also act as the abstraction on top of sharding, so that the control plane continue
+to see a Tenant as a single object, even though the reality is that it is many
+TenantShards.
+
+For the rest of this RFC, think of the Pageserver Controller as a component of
+the control plane.  The actual implementation is beyond the scope of this RFC
+and will be described in more detail elsewhere.
+
+### Safekeeper changes
+
+The safekeeper's API for subscribing to a WAL will be extended to enable callers
+to provide a `ShardIdentity`.  In this mode it will only send WAL entries that
+fall within the keyspace belonging to the shard, and WAL entries that are to
+be mirrored to all shards.
+
+Metadata updates describing databases+relations are mirrored to
+all shards, and other WAL messages are only provided to the shard
+that owns the key being updated.  For any operation that updates multiple
+keys, it will be provided to all the shards whose key ranges intersect with
+one or more of the keys referenced in the WAL message.
+
+### Pageserver Controller
+
+### Endpoints
+
+Compute endpoints will need to:
+- Accept a ShardMap as part of their configuration from the control plane
+- Route pageserver requests according to that ShardMap
+
+### Control Plane
+
+#### Publishing ShardMap updates
+
+The control plane will provide an API for the pageserver controller to publish updates
+to the ShardMap for a tenant.  When such an update is provided, it will be used to
+update the configuration of any endpoints currently active for the tenant.
+
+The ShardMap will be opaque to the Control Plane: it doesn't need to do anything with it
+other than storing and passing on to endpoints.
+
+#### Attaching via the Pageserver Controller
+
+The Control Plane will issue attach/create API calls to the pageserver controller
+instead of directly to pageservers.  This will relieve the control plane of the need
+to know about sharding.
+
+#### Enabling sharding for large tenants
+
+When a Tenant is created, it is up to the control plane to provide a hint to
+the pageserver about how large it will be.  This may be implemented as a service tier,
+where users creating very large databases would be onboarded to the tier, and then
+the Tenants they create would be created with a larger number of shards.  For the
+general population of users we should continue to use 1 shard by default.
+
+## Next Steps
+
+Clearly, the mechanism described in this RFC has substantial limitations:
+- A) the number of shards in a tenant is defined at creation time.
+- B) data is not distributed across the LSN dimension
+
+To address `A`, a _splitting_ feature will later be added.  One shard can split its
+data into a number of children by doing a special compaction operation to generate
+image layers broken up child-shard-wise, and then writing out an index_part.json for
+each child.  This will then require coordination with the pageserver controller to
+safely attach these new child shards and then move them around to distribute work.
+The opposite _merging_ operation can also be imagined, but is unlikely to be implemented:
+once a Tenant has been sharded, there is little value in merging it again.
+
+To address `B`, it is envisaged to have some gossip mechanism for pageservers to communicate
+about their workload, and then a getpageatlsn offload mechanism where one pageserver can
+ask another to go read the necessary layers from remote storage to serve the read.  This
+requires relativly little coordination because it is read-only: any node can service any
+read.  All reads to a particular shard would still flow through one node, but the
+disk capactity & I/O impact of servicing the read would be distributed.
+
+## FAQ/Alternatives
+
+### Why stripe the data, rather than using contiguous ranges of keyspace for each shard?
+
+When a database is growing under a write workload, writes may predominantly hit the
+end of the keyspace, creating a bandwidth hotspot on that shard.  Similarly, if the user
+is intensively re-writing a particular relation, if that relation lived in a particular
+shard then it would not achieve our goal of distributing the write work across shards.
+
+### Why not proxy read requests through one pageserver, so that endpoints don't have to change?
+
+Two reasons:
+1. This would not achieve scale-out of network bandwidth: a busy tenant with a large
+   database would still cause a load hotspot on the pageserver routing its read requests. 
+2. Implementing a proxy model as a stop-gap would not be a cheap option, because
+   it requires making pageservers aware of their peers, and adding synchronisation to
+   keep pageservers aware of their peers as they come and go.
--- a/docs/rfcs/030-pageserver-controller-phase1.md
+++ b/docs/rfcs/030-pageserver-controller-phase1.md
@@ -0,0 +1,119 @@
+# Pageserver Controller Phase 1: Generations
+
+## Summary
+
+In the [generation numbers RFC](025-generation-numbers.md), it was proposed that
+the console/control plane would act as the central coordinator for issuing generation
+numbers.
+
+That approach has not proven practical, so this RFC proposes an alternative implementation
+where generation numbers are managed in a different service.
+
+Calls to generation-aware pageserver APIs like create/attach will call out to this
+new _pageserver controller_ to acquire generation numbers.  This service will also
+form the basis for satisfying future pageserver management requirements, such as
+coordinating sharding, doing automatic capacity balancing, and many more.
+
+## Motivation
+
+This is a dependency for delivering high availability.
+
+### Prior art
+
+None
+
+## Requirements
+
+- Provide a hook for the pageserver to use when it receives an attach/create/load API
+  call, which will yield a generation that is safe for the pageserver to use.
+- Implement the /re-attach and /validate APIs required for the generation numbers feature
+  to work. 
+
+## Non Goals
+
+- This is not intended to interact with any components other than the pageserver, or
+  to integrate with the broader control plane in any way.
+
+## Impacted Components
+
+pageserver, pageserver controller (new)
+
+## Implementation
+
+We may start from the minimal `attachment_service` used in automated tests.
+
+### Data store
+
+For generation numbers, we need a persistent, linearizable data store.  Postgres is sufficient for
+this: we already have postgres instances used for other control plane work.
+
+The storage for the Pageserver Controller will be independent of other components:
+it might use the same physical database server but would use an independent database.
+
+### Deployment
+
+There will be one instance per region.  In future we would aim to define the concept
+of a pageserver cluster and have one controller per cluster, but in the short term
+one per region will be functionally okay for current scale.
+
+The pageserver controller will be deployed within kubernetes, in the same way as
+the storage broker (which is currently via a [helm chart](https://github.com/neondatabase/helm-charts/tree/main/charts/neon-storage-broker)).
+
+### Security
+
+The pageserver controller's API will do authentication with JWT, the same as
+the pageserver's existing API.
+
+### Correctness
+
+It is essential that pageservers call into the controller at the _very start_ of
+handling attach/create/load API requests.  They should not do any work at all until
+they have acquired that generation number.
+
+If the call fails, they must retry: it is not safe to proceed without a generation number.
+
+## Future
+
+Having a call chain that goes `Control plane -> Pageserver -> Pageserver controller`
+is clearly a little strange: we are only doing this to avoid needing to make changes
+to the control plane.
+
+In future, we will change the control plane to call directly into the pageserver
+controller, which would then call onwards into the pageserver.  This would be a fairly
+small change to the controller, since all the logic around storing and updating
+generation numbers would stay the same: just the behavior of the API frontend
+would be different.
+
+The work to enable pageservers to communicate with the controller is not wasted,
+because they still communicate in that direction when invoking `/re-attach` 
+and `/validate`
+
+## Alternatives considered
+
+### Run in the console/control plane codebase
+
+The control plane is a large Go codebase that uses extensive code generation, and
+has to be quite generic to manage many different types of component.
+
+### Direct DB access
+
+We could have pageservers call directly into a shared database to acquire and update
+generation numbers (with carefully crafted transactions to protect against concurrent
+attaches getting the same generation, etc).   
+
+Pros:
+- No extra service required, simpler deployment
+
+Cons:
+- No future path to a cleaner architecture: the pageserver controller can be implemented
+  as an extensible place for implement more functionality in future, whereas a mechanism
+  to do generation numbers via SQL queries from the pageserver would be specialized
+  and the code would probably be disposed of in the relatively near future.
+- Puts onus entirely on SQL query correctness to mediate concurrent access.
+  The pageserver controller also has to be correct in this respect in case there
+  is more than one instance running, but it is much less likely to hit this path,
+  so the overall risk of issues is lower when using a central service.
+
+
+The main downside to that approach is that it doesn't provide the future path that
+the pageserver controller does
--- a/libs/compute_api/src/spec.rs
+++ b/libs/compute_api/src/spec.rs
@@ -89,6 +89,8 @@ impl RemoteExtSpec {
        &self,
        ext_name: &str,
        is_library: bool,
+        build_tag: &str,
+        pg_major_version: &str,
    ) -> anyhow::Result<(String, RemotePath)> {
        let mut real_ext_name = ext_name;
        if is_library {
@@ -104,11 +106,32 @@ impl RemoteExtSpec {
                .ok_or(anyhow::anyhow!("library {} is not found", lib_raw_name))?;
        }

+        // Check if extension is present in public or custom.
+        // If not, then it is not allowed to be used by this compute.
+        if let Some(public_extensions) = &self.public_extensions {
+            if !public_extensions.contains(&real_ext_name.to_string()) {
+                if let Some(custom_extensions) = &self.custom_extensions {
+                    if !custom_extensions.contains(&real_ext_name.to_string()) {
+                        return Err(anyhow::anyhow!("extension {} is not found", real_ext_name));
+                    }
+                }
+            }
+        }
+
        match self.extension_data.get(real_ext_name) {
-            Some(ext_data) => Ok((
-                real_ext_name.to_string(),
-                RemotePath::from_string(&ext_data.archive_path)?,
-            )),
+            Some(_ext_data) => {
+                // Construct the path to the extension archive
+                // BUILD_TAG/PG_MAJOR_VERSION/extensions/EXTENSION_NAME.tar.zst
+                //
+                // Keep it in sync with path generation in
+                // https://github.com/neondatabase/build-custom-extensions/tree/main
+                let archive_path_str =
+                    format!("{build_tag}/{pg_major_version}/extensions/{real_ext_name}.tar.zst");
+                Ok((
+                    real_ext_name.to_string(),
+                    RemotePath::from_string(&archive_path_str)?,
+                ))
+            }
            None => Err(anyhow::anyhow!(
                "real_ext_name {} is not found",
                real_ext_name
--- a/libs/consumption_metrics/src/lib.rs
+++ b/libs/consumption_metrics/src/lib.rs
@@ -3,9 +3,9 @@
 //!
 use chrono::{DateTime, Utc};
 use rand::Rng;
-use serde::Serialize;
+use serde::{Deserialize, Serialize};

-#[derive(Serialize, Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Serialize, serde::Deserialize, Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
 #[serde(tag = "type")]
 pub enum EventType {
    #[serde(rename = "absolute")]
@@ -27,7 +27,8 @@ impl EventType {
    }

    pub fn incremental_timerange(&self) -> Option<std::ops::Range<&DateTime<Utc>>> {
-        // these can most likely be thought of as Range or RangeFull
+        // these can most likely be thought of as Range or RangeFull, at least pageserver creates
+        // incremental ranges where the stop and next start are equal.
        use EventType::*;
        match self {
            Incremental {
@@ -41,15 +42,25 @@ impl EventType {
    pub fn is_incremental(&self) -> bool {
        matches!(self, EventType::Incremental { .. })
    }
+
+    /// Returns the absolute time, or for incremental ranges, the stop time.
+    pub fn recorded_at(&self) -> &DateTime<Utc> {
+        use EventType::*;
+
+        match self {
+            Absolute { time } => time,
+            Incremental { stop_time, .. } => stop_time,
+        }
+    }
 }

-#[derive(Serialize, Debug, Clone, Eq, PartialEq, Ord, PartialOrd)]
-pub struct Event<Extra> {
+#[derive(Serialize, Deserialize, Debug, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub struct Event<Extra, Metric> {
    #[serde(flatten)]
    #[serde(rename = "type")]
    pub kind: EventType,

-    pub metric: &'static str,
+    pub metric: Metric,
    pub idempotency_key: String,
    pub value: u64,

@@ -58,12 +69,38 @@ pub struct Event<Extra> {
 }

 pub fn idempotency_key(node_id: &str) -> String {
-    format!(
-        "{}-{}-{:04}",
-        Utc::now(),
-        node_id,
-        rand::thread_rng().gen_range(0..=9999)
-    )
+    IdempotencyKey::generate(node_id).to_string()
+}
+
+/// Downstream users will use these to detect upload retries.
+pub struct IdempotencyKey<'a> {
+    now: chrono::DateTime<Utc>,
+    node_id: &'a str,
+    nonce: u16,
+}
+
+impl std::fmt::Display for IdempotencyKey<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}-{}-{:04}", self.now, self.node_id, self.nonce)
+    }
+}
+
+impl<'a> IdempotencyKey<'a> {
+    pub fn generate(node_id: &'a str) -> Self {
+        IdempotencyKey {
+            now: Utc::now(),
+            node_id,
+            nonce: rand::thread_rng().gen_range(0..=9999),
+        }
+    }
+
+    pub fn for_tests(now: DateTime<Utc>, node_id: &'a str, nonce: u16) -> Self {
+        IdempotencyKey {
+            now,
+            node_id,
+            nonce,
+        }
+    }
 }

 pub const CHUNK_SIZE: usize = 1000;
--- a/libs/pageserver_api/src/control_api.rs
+++ b/libs/pageserver_api/src/control_api.rs
@@ -0,0 +1,52 @@
+//! Types in this file are for pageserver's upward-facing API calls to the control plane,
+//! required for acquiring and validating tenant generation numbers.
+//!
+//! See docs/rfcs/025-generation-numbers.md
+
+use serde::{Deserialize, Serialize};
+use serde_with::{serde_as, DisplayFromStr};
+use utils::id::{NodeId, TenantId};
+
+#[derive(Serialize, Deserialize)]
+pub struct ReAttachRequest {
+    pub node_id: NodeId,
+}
+
+#[serde_as]
+#[derive(Serialize, Deserialize)]
+pub struct ReAttachResponseTenant {
+    #[serde_as(as = "DisplayFromStr")]
+    pub id: TenantId,
+    pub generation: u32,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct ReAttachResponse {
+    pub tenants: Vec<ReAttachResponseTenant>,
+}
+
+#[serde_as]
+#[derive(Serialize, Deserialize)]
+pub struct ValidateRequestTenant {
+    #[serde_as(as = "DisplayFromStr")]
+    pub id: TenantId,
+    pub gen: u32,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct ValidateRequest {
+    pub tenants: Vec<ValidateRequestTenant>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct ValidateResponse {
+    pub tenants: Vec<ValidateResponseTenant>,
+}
+
+#[serde_as]
+#[derive(Serialize, Deserialize)]
+pub struct ValidateResponseTenant {
+    #[serde_as(as = "DisplayFromStr")]
+    pub id: TenantId,
+    pub valid: bool,
+}
--- a/libs/pageserver_api/src/lib.rs
+++ b/libs/pageserver_api/src/lib.rs
@@ -1,6 +1,7 @@
 use const_format::formatcp;

 /// Public API types
+pub mod control_api;
 pub mod models;
 pub mod reltag;

--- a/libs/pageserver_api/src/models.rs
+++ b/libs/pageserver_api/src/models.rs
@@ -194,10 +194,22 @@ pub struct TimelineCreateRequest {
 pub struct TenantCreateRequest {
    #[serde_as(as = "DisplayFromStr")]
    pub new_tenant_id: TenantId,
+    #[serde(default)]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub generation: Option<u32>,
    #[serde(flatten)]
    pub config: TenantConfig, // as we have a flattened field, we should reject all unknown fields in it
 }

+#[serde_as]
+#[derive(Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct TenantLoadRequest {
+    #[serde(default)]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub generation: Option<u32>,
+}
+
 impl std::ops::Deref for TenantCreateRequest {
    type Target = TenantConfig;

@@ -241,15 +253,6 @@ pub struct StatusResponse {
    pub id: NodeId,
 }

-impl TenantCreateRequest {
-    pub fn new(new_tenant_id: TenantId) -> TenantCreateRequest {
-        TenantCreateRequest {
-            new_tenant_id,
-            config: TenantConfig::default(),
-        }
-    }
-}
-
 #[serde_as]
 #[derive(Serialize, Deserialize, Debug)]
 #[serde(deny_unknown_fields)]
@@ -293,9 +296,11 @@ impl TenantConfigRequest {
    }
 }

-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Deserialize)]
 pub struct TenantAttachRequest {
    pub config: TenantAttachConfig,
+    #[serde(default)]
+    pub generation: Option<u32>,
 }

 /// Newtype to enforce deny_unknown_fields on TenantConfig for
@@ -376,6 +381,8 @@ pub struct TimelineInfo {
    pub pg_version: u32,

    pub state: TimelineState,
+
+    pub walreceiver_status: String,
 }

 #[derive(Debug, Clone, Serialize)]
--- a/libs/postgres_ffi/README.md
+++ b/libs/postgres_ffi/README.md
@@ -10,9 +10,11 @@ should be auto-generated too, but that's a TODO.
 The PostgreSQL on-disk file format is not portable across different
 CPU architectures and operating systems. It is also subject to change
 in each major PostgreSQL version. Currently, this module supports
-PostgreSQL v14 and v15: bindings and code that depends on them are version-specific.
-This code is organized in modules: `postgres_ffi::v14` and `postgres_ffi::v15`
-Version independend code is explicitly exported into shared `postgres_ffi`.
+PostgreSQL v14, v15 and v16: bindings and code that depends on them are
+version-specific.
+This code is organized in modules `postgres_ffi::v14`, `postgres_ffi::v15` and
+`postgres_ffi::v16`. Version independent code is explicitly exported into
+shared `postgres_ffi`.


 TODO: Currently, there is also some code that deals with WAL records
--- a/libs/postgres_ffi/build.rs
+++ b/libs/postgres_ffi/build.rs
@@ -56,7 +56,7 @@ fn main() -> anyhow::Result<()> {
        PathBuf::from("pg_install")
    };

-    for pg_version in &["v14", "v15"] {
+    for pg_version in &["v14", "v15", "v16"] {
        let mut pg_install_dir_versioned = pg_install_dir.join(pg_version);
        if pg_install_dir_versioned.is_relative() {
            let cwd = env::current_dir().context("Failed to get current_dir")?;
@@ -125,6 +125,7 @@ fn main() -> anyhow::Result<()> {
            .allowlist_var("PG_CONTROLFILEDATA_OFFSETOF_CRC")
            .allowlist_type("PageHeaderData")
            .allowlist_type("DBState")
+            .allowlist_type("RelMapFile")
            // Because structs are used for serialization, tell bindgen to emit
            // explicit padding fields.
            .explicit_padding(true)
--- a/libs/postgres_ffi/src/lib.rs
+++ b/libs/postgres_ffi/src/lib.rs
@@ -51,11 +51,59 @@ macro_rules! for_all_postgres_versions {
    ($macro:tt) => {
        $macro!(v14);
        $macro!(v15);
+        $macro!(v16);
    };
 }

 for_all_postgres_versions! { postgres_ffi }

+/// dispatch_pgversion
+///
+/// Run a code block in a context where the postgres_ffi bindings for a
+/// specific (supported) PostgreSQL version are `use`-ed in scope under the pgv
+/// identifier.
+/// If the provided pg_version is not supported, we panic!(), unless the
+/// optional third argument was provided (in which case that code will provide
+/// the default handling instead).
+///
+/// Use like
+///
+/// dispatch_pgversion!(my_pgversion, { pgv::constants::XLOG_DBASE_CREATE })
+/// dispatch_pgversion!(my_pgversion, pgv::constants::XLOG_DBASE_CREATE)
+///
+/// Other uses are for macro-internal purposes only and strictly unsupported.
+///
+#[macro_export]
+macro_rules! dispatch_pgversion {
+    ($version:expr, $code:expr) => {
+        dispatch_pgversion!($version, $code, panic!("Unknown PostgreSQL version {}", $version))
+    };
+    ($version:expr, $code:expr, $invalid_pgver_handling:expr) => {
+        dispatch_pgversion!(
+            $version => $code,
+            default = $invalid_pgver_handling,
+            pgversions = [
+                14 : v14,
+                15 : v15,
+                16 : v16,
+            ]
+        )
+    };
+    ($pgversion:expr => $code:expr,
+     default = $default:expr,
+     pgversions = [$($sv:literal : $vsv:ident),+ $(,)?]) => {
+        match ($pgversion) {
+            $($sv => {
+                use $crate::$vsv as pgv;
+                $code
+            },)+
+            _ => {
+                $default
+            }
+        }
+    };
+}
+
 pub mod pg_constants;
 pub mod relfile_utils;

@@ -90,13 +138,7 @@ pub use v14::xlog_utils::XLogFileName;
 pub use v14::bindings::DBState_DB_SHUTDOWNED;

 pub fn bkpimage_is_compressed(bimg_info: u8, version: u32) -> anyhow::Result<bool> {
-    match version {
-        14 => Ok(bimg_info & v14::bindings::BKPIMAGE_IS_COMPRESSED != 0),
-        15 => Ok(bimg_info & v15::bindings::BKPIMAGE_COMPRESS_PGLZ != 0
-            || bimg_info & v15::bindings::BKPIMAGE_COMPRESS_LZ4 != 0
-            || bimg_info & v15::bindings::BKPIMAGE_COMPRESS_ZSTD != 0),
-        _ => anyhow::bail!("Unknown version {}", version),
-    }
+    dispatch_pgversion!(version, Ok(pgv::bindings::bkpimg_is_compressed(bimg_info)))
 }

 pub fn generate_wal_segment(
@@ -107,11 +149,11 @@ pub fn generate_wal_segment(
 ) -> Result<Bytes, SerializeError> {
    assert_eq!(segno, lsn.segment_number(WAL_SEGMENT_SIZE));

-    match pg_version {
-        14 => v14::xlog_utils::generate_wal_segment(segno, system_id, lsn),
-        15 => v15::xlog_utils::generate_wal_segment(segno, system_id, lsn),
-        _ => Err(SerializeError::BadInput),
-    }
+    dispatch_pgversion!(
+        pg_version,
+        pgv::xlog_utils::generate_wal_segment(segno, system_id, lsn),
+        Err(SerializeError::BadInput)
+    )
 }

 pub fn generate_pg_control(
@@ -120,11 +162,11 @@ pub fn generate_pg_control(
    lsn: Lsn,
    pg_version: u32,
 ) -> anyhow::Result<(Bytes, u64)> {
-    match pg_version {
-        14 => v14::xlog_utils::generate_pg_control(pg_control_bytes, checkpoint_bytes, lsn),
-        15 => v15::xlog_utils::generate_pg_control(pg_control_bytes, checkpoint_bytes, lsn),
-        _ => anyhow::bail!("Unknown version {}", pg_version),
-    }
+    dispatch_pgversion!(
+        pg_version,
+        pgv::xlog_utils::generate_pg_control(pg_control_bytes, checkpoint_bytes, lsn),
+        anyhow::bail!("Unknown version {}", pg_version)
+    )
 }

 // PG timeline is always 1, changing it doesn't have any useful meaning in Neon.
@@ -196,8 +238,6 @@ pub fn fsm_logical_to_physical(addr: BlockNumber) -> BlockNumber {
 }

 pub mod waldecoder {
-
-    use crate::{v14, v15};
    use bytes::{Buf, Bytes, BytesMut};
    use std::num::NonZeroU32;
    use thiserror::Error;
@@ -248,22 +288,17 @@ pub mod waldecoder {
        }

        pub fn poll_decode(&mut self) -> Result<Option<(Lsn, Bytes)>, WalDecodeError> {
-            match self.pg_version {
-                // This is a trick to support both versions simultaneously.
-                // See WalStreamDecoderHandler comments.
-                14 => {
-                    use self::v14::waldecoder_handler::WalStreamDecoderHandler;
+            dispatch_pgversion!(
+                self.pg_version,
+                {
+                    use pgv::waldecoder_handler::WalStreamDecoderHandler;
                    self.poll_decode_internal()
-                }
-                15 => {
-                    use self::v15::waldecoder_handler::WalStreamDecoderHandler;
-                    self.poll_decode_internal()
-                }
-                _ => Err(WalDecodeError {
+                },
+                Err(WalDecodeError {
                    msg: format!("Unknown version {}", self.pg_version),
                    lsn: self.lsn,
-                }),
-            }
+                })
+            )
        }
    }
 }
--- a/libs/postgres_ffi/src/pg_constants.rs
+++ b/libs/postgres_ffi/src/pg_constants.rs
@@ -137,9 +137,12 @@ pub const XLOG_HEAP_INSERT: u8 = 0x00;
 pub const XLOG_HEAP_DELETE: u8 = 0x10;
 pub const XLOG_HEAP_UPDATE: u8 = 0x20;
 pub const XLOG_HEAP_HOT_UPDATE: u8 = 0x40;
+pub const XLOG_HEAP_LOCK: u8 = 0x60;
 pub const XLOG_HEAP_INIT_PAGE: u8 = 0x80;
 pub const XLOG_HEAP2_VISIBLE: u8 = 0x40;
 pub const XLOG_HEAP2_MULTI_INSERT: u8 = 0x50;
+pub const XLOG_HEAP2_LOCK_UPDATED: u8 = 0x60;
+pub const XLH_LOCK_ALL_FROZEN_CLEARED: u8 = 0x01;
 pub const XLH_INSERT_ALL_FROZEN_SET: u8 = (1 << 5) as u8;
 pub const XLH_INSERT_ALL_VISIBLE_CLEARED: u8 = (1 << 0) as u8;
 pub const XLH_UPDATE_OLD_ALL_VISIBLE_CLEARED: u8 = (1 << 0) as u8;
@@ -163,6 +166,20 @@ pub const RM_HEAP2_ID: u8 = 9;
 pub const RM_HEAP_ID: u8 = 10;
 pub const RM_LOGICALMSG_ID: u8 = 21;

+// from neon_rmgr.h
+pub const RM_NEON_ID: u8 = 134;
+
+pub const XLOG_NEON_HEAP_INIT_PAGE: u8 = 0x80;
+
+pub const XLOG_NEON_HEAP_INSERT: u8 = 0x00;
+pub const XLOG_NEON_HEAP_DELETE: u8 = 0x10;
+pub const XLOG_NEON_HEAP_UPDATE: u8 = 0x20;
+pub const XLOG_NEON_HEAP_HOT_UPDATE: u8 = 0x30;
+pub const XLOG_NEON_HEAP_LOCK: u8 = 0x40;
+pub const XLOG_NEON_HEAP_MULTI_INSERT: u8 = 0x50;
+
+pub const XLOG_NEON_HEAP_VISIBLE: u8 = 0x40;
+
 // from xlogreader.h
 pub const XLR_INFO_MASK: u8 = 0x0F;
 pub const XLR_RMGR_INFO_MASK: u8 = 0xF0;
--- a/libs/postgres_ffi/src/pg_constants_v14.rs
+++ b/libs/postgres_ffi/src/pg_constants_v14.rs
@@ -3,3 +3,8 @@ pub const XLOG_DBASE_DROP: u8 = 0x10;

 pub const BKPIMAGE_IS_COMPRESSED: u8 = 0x02; /* page image is compressed */
 pub const BKPIMAGE_APPLY: u8 = 0x04; /* page image should be restored during replay */
+pub const SIZEOF_RELMAPFILE: usize = 512; /* sizeof(RelMapFile) in relmapper.c */
+
+pub fn bkpimg_is_compressed(bimg_info: u8) -> bool {
+    (bimg_info & BKPIMAGE_IS_COMPRESSED) != 0
+}
--- a/libs/postgres_ffi/src/pg_constants_v15.rs
+++ b/libs/postgres_ffi/src/pg_constants_v15.rs
@@ -1,10 +1,18 @@
 pub const XACT_XINFO_HAS_DROPPED_STATS: u32 = 1u32 << 8;

 pub const XLOG_DBASE_CREATE_FILE_COPY: u8 = 0x00;
-pub const XLOG_DBASE_CREATE_WAL_LOG: u8 = 0x00;
+pub const XLOG_DBASE_CREATE_WAL_LOG: u8 = 0x10;
 pub const XLOG_DBASE_DROP: u8 = 0x20;

 pub const BKPIMAGE_APPLY: u8 = 0x02; /* page image should be restored during replay */
 pub const BKPIMAGE_COMPRESS_PGLZ: u8 = 0x04; /* page image is compressed */
 pub const BKPIMAGE_COMPRESS_LZ4: u8 = 0x08; /* page image is compressed */
 pub const BKPIMAGE_COMPRESS_ZSTD: u8 = 0x10; /* page image is compressed */
+
+pub const SIZEOF_RELMAPFILE: usize = 512; /* sizeof(RelMapFile) in relmapper.c */
+
+pub fn bkpimg_is_compressed(bimg_info: u8) -> bool {
+    const ANY_COMPRESS_FLAG: u8 = BKPIMAGE_COMPRESS_PGLZ | BKPIMAGE_COMPRESS_LZ4 | BKPIMAGE_COMPRESS_ZSTD;
+
+    (bimg_info & ANY_COMPRESS_FLAG) != 0
+}
--- a/libs/postgres_ffi/src/pg_constants_v16.rs
+++ b/libs/postgres_ffi/src/pg_constants_v16.rs
@@ -0,0 +1,18 @@
+pub const XACT_XINFO_HAS_DROPPED_STATS: u32 = 1u32 << 8;
+
+pub const XLOG_DBASE_CREATE_FILE_COPY: u8 = 0x00;
+pub const XLOG_DBASE_CREATE_WAL_LOG: u8 = 0x10;
+pub const XLOG_DBASE_DROP: u8 = 0x20;
+
+pub const BKPIMAGE_APPLY: u8 = 0x02; /* page image should be restored during replay */
+pub const BKPIMAGE_COMPRESS_PGLZ: u8 = 0x04; /* page image is compressed */
+pub const BKPIMAGE_COMPRESS_LZ4: u8 = 0x08; /* page image is compressed */
+pub const BKPIMAGE_COMPRESS_ZSTD: u8 = 0x10; /* page image is compressed */
+
+pub const SIZEOF_RELMAPFILE: usize = 524; /* sizeof(RelMapFile) in relmapper.c */
+
+pub fn bkpimg_is_compressed(bimg_info: u8) -> bool {
+    const ANY_COMPRESS_FLAG: u8 = BKPIMAGE_COMPRESS_PGLZ | BKPIMAGE_COMPRESS_LZ4 | BKPIMAGE_COMPRESS_ZSTD;
+
+    (bimg_info & ANY_COMPRESS_FLAG) != 0
+}
--- a/libs/postgres_ffi/wal_craft/src/lib.rs
+++ b/libs/postgres_ffi/wal_craft/src/lib.rs
@@ -49,9 +49,9 @@ impl Conf {
    pub fn pg_distrib_dir(&self) -> anyhow::Result<PathBuf> {
        let path = self.pg_distrib_dir.clone();

+        #[allow(clippy::manual_range_patterns)]
        match self.pg_version {
-            14 => Ok(path.join(format!("v{}", self.pg_version))),
-            15 => Ok(path.join(format!("v{}", self.pg_version))),
+            14 | 15 | 16 => Ok(path.join(format!("v{}", self.pg_version))),
            _ => bail!("Unsupported postgres version: {}", self.pg_version),
        }
    }
@@ -250,11 +250,18 @@ fn craft_internal<C: postgres::GenericClient>(
    let (mut intermediate_lsns, last_lsn) = f(client, initial_lsn)?;
    let last_lsn = match last_lsn {
        None => client.pg_current_wal_insert_lsn()?,
-        Some(last_lsn) => match last_lsn.cmp(&client.pg_current_wal_insert_lsn()?) {
-            Ordering::Less => bail!("Some records were inserted after the crafted WAL"),
-            Ordering::Equal => last_lsn,
-            Ordering::Greater => bail!("Reported LSN is greater than insert_lsn"),
-        },
+        Some(last_lsn) => {
+            let insert_lsn = client.pg_current_wal_insert_lsn()?;
+            match last_lsn.cmp(&insert_lsn) {
+                Ordering::Less => bail!(
+                    "Some records were inserted after the crafted WAL: {} vs {}",
+                    last_lsn,
+                    insert_lsn
+                ),
+                Ordering::Equal => last_lsn,
+                Ordering::Greater => bail!("Reported LSN is greater than insert_lsn"),
+            }
+        }
    };
    if !intermediate_lsns.starts_with(&[initial_lsn]) {
        intermediate_lsns.insert(0, initial_lsn);
@@ -363,8 +370,9 @@ impl Crafter for LastWalRecordXlogSwitchEndsOnPageBoundary {
        );
        ensure!(
            u64::from(after_xlog_switch) as usize % XLOG_BLCKSZ == XLOG_SIZE_OF_XLOG_SHORT_PHD,
-            "XLOG_SWITCH message ended not on page boundary: {}",
-            after_xlog_switch
+            "XLOG_SWITCH message ended not on page boundary: {}, offset = {}",
+            after_xlog_switch,
+            u64::from(after_xlog_switch) as usize % XLOG_BLCKSZ
        );
        Ok((vec![before_xlog_switch, after_xlog_switch], next_segment))
    }
--- a/libs/pq_proto/src/lib.rs
+++ b/libs/pq_proto/src/lib.rs
@@ -959,7 +959,7 @@ mod tests {
        let make_params = |options| StartupMessageParams::new([("options", options)]);

        let params = StartupMessageParams::new([]);
-        assert!(matches!(params.options_escaped(), None));
+        assert!(params.options_escaped().is_none());

        let params = make_params("");
        assert!(split_options(&params).is_empty());
--- a/libs/remote_storage/src/local_fs.rs
+++ b/libs/remote_storage/src/local_fs.rs
@@ -148,21 +148,55 @@ impl RemoteStorage for LocalFs {
            Some(folder) => folder.with_base(&self.storage_root),
            None => self.storage_root.clone(),
        };
-        let mut files = vec![];
-        let mut directory_queue = vec![full_path.clone()];

+        // If we were given a directory, we may use it as our starting point.
+        // Otherwise, we must go up to the parent directory.  This is because
+        // S3 object list prefixes can be arbitrary strings, but when reading
+        // the local filesystem we need a directory to start calling read_dir on.
+        let mut initial_dir = full_path.clone();
+        match fs::metadata(full_path.clone()).await {
+            Ok(meta) => {
+                if !meta.is_dir() {
+                    // It's not a directory: strip back to the parent
+                    initial_dir.pop();
+                }
+            }
+            Err(e) if e.kind() == ErrorKind::NotFound => {
+                // It's not a file that exists: strip the prefix back to the parent directory
+                initial_dir.pop();
+            }
+            Err(e) => {
+                // Unexpected I/O error
+                anyhow::bail!(e)
+            }
+        }
+
+        // Note that PathBuf starts_with only considers full path segments, but
+        // object prefixes are arbitrary strings, so we need the strings for doing
+        // starts_with later.
+        let prefix = full_path.to_string_lossy();
+
+        let mut files = vec![];
+        let mut directory_queue = vec![initial_dir.clone()];
        while let Some(cur_folder) = directory_queue.pop() {
            let mut entries = fs::read_dir(cur_folder.clone()).await?;
            while let Some(entry) = entries.next_entry().await? {
                let file_name: PathBuf = entry.file_name().into();
                let full_file_name = cur_folder.clone().join(&file_name);
-                let file_remote_path = self.local_file_to_relative_path(full_file_name.clone());
-                files.push(file_remote_path.clone());
-                if full_file_name.is_dir() {
-                    directory_queue.push(full_file_name);
+                if full_file_name
+                    .to_str()
+                    .map(|s| s.starts_with(prefix.as_ref()))
+                    .unwrap_or(false)
+                {
+                    let file_remote_path = self.local_file_to_relative_path(full_file_name.clone());
+                    files.push(file_remote_path.clone());
+                    if full_file_name.is_dir() {
+                        directory_queue.push(full_file_name);
+                    }
                }
            }
        }
+
        Ok(files)
    }

--- a/libs/remote_storage/src/s3_bucket.rs
+++ b/libs/remote_storage/src/s3_bucket.rs
@@ -573,7 +573,7 @@ mod tests {

    #[test]
    fn relative_path() {
-        let all_paths = vec!["", "some/path", "some/path/"];
+        let all_paths = ["", "some/path", "some/path/"];
        let all_paths: Vec<RemotePath> = all_paths
            .iter()
            .map(|x| RemotePath::new(Path::new(x)).expect("bad path"))
--- a/libs/utils/scripts/restore_from_wal.sh
+++ b/libs/utils/scripts/restore_from_wal.sh
@@ -9,11 +9,12 @@ PORT=$4
 SYSID=$(od -A n -j 24 -N 8 -t d8 "$WAL_PATH"/000000010000000000000002* | cut -c 3-)
 rm -fr "$DATA_DIR"
 env -i LD_LIBRARY_PATH="$PG_BIN"/../lib "$PG_BIN"/initdb -E utf8 -U cloud_admin -D "$DATA_DIR" --sysid="$SYSID"
-echo port="$PORT" >> "$DATA_DIR"/postgresql.conf
+echo "port=$PORT" >> "$DATA_DIR"/postgresql.conf
+echo "shared_preload_libraries='\$libdir/neon_rmgr.so'" >> "$DATA_DIR"/postgresql.conf
 REDO_POS=0x$("$PG_BIN"/pg_controldata -D "$DATA_DIR" | grep -F "REDO location"| cut -c 42-)
 declare -i WAL_SIZE=$REDO_POS+114
-"$PG_BIN"/pg_ctl -D "$DATA_DIR" -l logfile start
-"$PG_BIN"/pg_ctl -D "$DATA_DIR" -l logfile stop -m immediate
+"$PG_BIN"/pg_ctl -D "$DATA_DIR" -l "$DATA_DIR/logfile.log" start
+"$PG_BIN"/pg_ctl -D "$DATA_DIR" -l "$DATA_DIR/logfile.log" stop -m immediate
 cp "$DATA_DIR"/pg_wal/000000010000000000000001 .
 cp "$WAL_PATH"/* "$DATA_DIR"/pg_wal/
 for partial in "$DATA_DIR"/pg_wal/*.partial ; do mv "$partial" "${partial%.partial}" ; done
--- a/libs/utils/src/generation.rs
+++ b/libs/utils/src/generation.rs
@@ -0,0 +1,138 @@
+use std::fmt::Debug;
+
+use serde::{Deserialize, Serialize};
+
+/// Tenant generations are used to provide split-brain safety and allow
+/// multiple pageservers to attach the same tenant concurrently.
+///
+/// See docs/rfcs/025-generation-numbers.md for detail on how generation
+/// numbers are used.
+#[derive(Copy, Clone, Eq, PartialEq, PartialOrd, Ord)]
+pub enum Generation {
+    // Generations with this magic value will not add a suffix to S3 keys, and will not
+    // be included in persisted index_part.json.  This value is only to be used
+    // during migration from pre-generation metadata to generation-aware metadata,
+    // and should eventually go away.
+    //
+    // A special Generation is used rather than always wrapping Generation in an Option,
+    // so that code handling generations doesn't have to be aware of the legacy
+    // case everywhere it touches a generation.
+    None,
+    // Generations with this magic value may never be used to construct S3 keys:
+    // we will panic if someone tries to.  This is for Tenants in the "Broken" state,
+    // so that we can satisfy their constructor with a Generation without risking
+    // a code bug using it in an S3 write (broken tenants should never write)
+    Broken,
+    Valid(u32),
+}
+
+/// The Generation type represents a number associated with a Tenant, which
+/// increments every time the tenant is attached to a new pageserver, or
+/// an attached pageserver restarts.
+///
+/// It is included as a suffix in S3 keys, as a protection against split-brain
+/// scenarios where pageservers might otherwise issue conflicting writes to
+/// remote storage
+impl Generation {
+    /// Create a new Generation that represents a legacy key format with
+    /// no generation suffix
+    pub fn none() -> Self {
+        Self::None
+    }
+
+    // Create a new generation that will panic if you try to use get_suffix
+    pub fn broken() -> Self {
+        Self::Broken
+    }
+
+    pub fn new(v: u32) -> Self {
+        Self::Valid(v)
+    }
+
+    pub fn is_none(&self) -> bool {
+        matches!(self, Self::None)
+    }
+
+    #[track_caller]
+    pub fn get_suffix(&self) -> String {
+        match self {
+            Self::Valid(v) => {
+                format!("-{:08x}", v)
+            }
+            Self::None => "".into(),
+            Self::Broken => {
+                panic!("Tried to use a broken generation");
+            }
+        }
+    }
+
+    /// `suffix` is the part after "-" in a key
+    ///
+    /// Returns None if parsing was unsuccessful
+    pub fn parse_suffix(suffix: &str) -> Option<Generation> {
+        u32::from_str_radix(suffix, 16).map(Generation::new).ok()
+    }
+
+    #[track_caller]
+    pub fn previous(&self) -> Generation {
+        match self {
+            Self::Valid(n) => {
+                if *n == 0 {
+                    // Since a tenant may be upgraded from a pre-generations state, interpret the "previous" generation
+                    // to 0 as being "no generation".
+                    Self::None
+                } else {
+                    Self::Valid(n - 1)
+                }
+            }
+            Self::None => Self::None,
+            Self::Broken => panic!("Attempted to use a broken generation"),
+        }
+    }
+}
+
+impl Serialize for Generation {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        if let Self::Valid(v) = self {
+            v.serialize(serializer)
+        } else {
+            // We should never be asked to serialize a None or Broken.  Structures
+            // that include an optional generation should convert None to an
+            // Option<Generation>::None
+            Err(serde::ser::Error::custom(
+                "Tried to serialize invalid generation ({self})",
+            ))
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for Generation {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        Ok(Self::Valid(u32::deserialize(deserializer)?))
+    }
+}
+
+// We intentionally do not implement Display for Generation, to reduce the
+// risk of a bug where the generation is used in a format!() string directly
+// instead of using get_suffix().
+impl Debug for Generation {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Valid(v) => {
+                write!(f, "{:08x}", v)
+            }
+            Self::None => {
+                write!(f, "<none>")
+            }
+            Self::Broken => {
+                write!(f, "<broken>")
+            }
+        }
+    }
+}
--- a/libs/utils/src/lib.rs
+++ b/libs/utils/src/lib.rs
@@ -27,6 +27,9 @@ pub mod id;
 // http endpoint utils
 pub mod http;

+// definition of the Generation type for pageserver attachment APIs
+pub mod generation;
+
 // common log initialisation routine
 pub mod logging;

--- a/libs/vm_monitor/src/cgroup.rs
+++ b/libs/vm_monitor/src/cgroup.rs
@@ -315,12 +315,8 @@ impl CgroupWatcher {
    where
        E: Stream<Item = Sequenced<u64>>,
    {
-        // There are several actions might do when receiving a `memory.high`,
-        // such as freezing the cgroup, or increasing its `memory.high`. We don't
-        // want to do these things too often (because postgres needs to run, and
-        // we only have so much memory). These timers serve as rate limits for this.
        let mut wait_to_freeze = pin!(tokio::time::sleep(Duration::ZERO));
-        let mut wait_to_increase_memory_high = pin!(tokio::time::sleep(Duration::ZERO));
+        let mut last_memory_high_increase_at: Option<Instant> = None;
        let mut events = pin!(events);

        // Are we waiting to be upscaled? Could be true if we request upscale due
@@ -332,6 +328,8 @@ impl CgroupWatcher {
                upscale = upscales.recv() => {
                    let Sequenced { seqnum, data } = upscale
                        .context("failed to listen on upscale notification channel")?;
+                    waiting_on_upscale = false;
+                    last_memory_high_increase_at = None;
                    self.last_upscale_seqnum.store(seqnum, Ordering::Release);
                    info!(cpu = data.cpu, mem_bytes = data.mem, "received upscale");
                }
@@ -396,12 +394,17 @@ impl CgroupWatcher {
                            .send(())
                            .await
                            .context("failed to request upscale")?;
+                        waiting_on_upscale = true;
                        continue;
                    }

                    // Shoot, we can't freeze or and we're still waiting on upscale,
                    // increase memory.high to reduce throttling
-                    if wait_to_increase_memory_high.is_elapsed() {
+                    let can_increase_memory_high = match last_memory_high_increase_at {
+                        None => true,
+                        Some(t) => t.elapsed() > self.config.memory_high_increase_every,
+                    };
+                    if can_increase_memory_high {
                        info!(
                            "received memory.high event, \
                            but too soon to refreeze and already requested upscale \
@@ -437,12 +440,11 @@ impl CgroupWatcher {
                        );
                        self.set_high_bytes(new_high)
                            .context("failed to set memory.high")?;
-                        wait_to_increase_memory_high
-                            .as_mut()
-                            .reset(Instant::now() + self.config.memory_high_increase_every)
+                        last_memory_high_increase_at = Some(Instant::now());
+                        continue;
                    }

-                    // we can't do anything
+                    info!("received memory.high event, but can't do anything");
                }
            };
        }
@@ -559,14 +561,7 @@ impl CgroupWatcher {
 /// Setting these values also affects the thresholds for receiving usage alerts.
 #[derive(Debug)]
 pub struct MemoryLimits {
-    high: u64,
-    max: u64,
-}
-
-impl MemoryLimits {
-    pub fn new(high: u64, max: u64) -> Self {
-        Self { max, high }
-    }
+    pub high: u64,
 }

 // Methods for manipulating the actual cgroup
@@ -643,12 +638,7 @@ impl CgroupWatcher {

    /// Set cgroup memory.high and memory.max.
    pub fn set_limits(&self, limits: &MemoryLimits) -> anyhow::Result<()> {
-        info!(
-            limits.high,
-            limits.max,
-            path = self.path(),
-            "writing new memory limits",
-        );
+        info!(limits.high, path = self.path(), "writing new memory limits",);
        self.memory()
            .context("failed to get memory subsystem while setting memory limits")?
            .set_mem(cgroups_rs::memory::SetMemory {
@@ -657,7 +647,7 @@ impl CgroupWatcher {
                high: Some(MaxValue::Value(
                    u64::min(limits.high, i64::MAX as u64) as i64
                )),
-                max: Some(MaxValue::Value(u64::min(limits.max, i64::MAX as u64) as i64)),
+                max: None,
            })
            .context("failed to set memory limits")
    }
@@ -665,7 +655,7 @@ impl CgroupWatcher {
    /// Given some amount of available memory, set the desired cgroup memory limits
    pub fn set_memory_limits(&mut self, available_memory: u64) -> anyhow::Result<()> {
        let new_high = self.config.calculate_memory_high_value(available_memory);
-        let limits = MemoryLimits::new(new_high, available_memory);
+        let limits = MemoryLimits { high: new_high };
        info!(
            path = self.path(),
            memory = ?limits,
--- a/libs/vm_monitor/src/lib.rs
+++ b/libs/vm_monitor/src/lib.rs
@@ -178,14 +178,17 @@ pub async fn ws_handler(

 /// Starts the monitor. If startup fails or the monitor exits, an error will
 /// be logged and our internal state will be reset to allow for new connections.
-#[tracing::instrument(skip_all, fields(?args))]
+#[tracing::instrument(skip_all)]
 async fn start_monitor(
    ws: WebSocket,
    args: &Args,
    kill: broadcast::Receiver<()>,
    token: CancellationToken,
 ) {
-    info!("accepted new websocket connection -> starting monitor");
+    info!(
+        ?args,
+        "accepted new websocket connection -> starting monitor"
+    );
    let timeout = Duration::from_secs(4);
    let monitor = tokio::time::timeout(
        timeout,
--- a/libs/vm_monitor/src/runner.rs
+++ b/libs/vm_monitor/src/runner.rs
@@ -5,6 +5,7 @@
 //! all functionality.

 use std::sync::Arc;
+use std::time::{Duration, Instant};
 use std::{fmt::Debug, mem};

 use anyhow::{bail, Context};
@@ -36,6 +37,8 @@ pub struct Runner {
    /// by us vs the autoscaler-agent.
    counter: usize,

+    last_upscale_request_at: Option<Instant>,
+
    /// A signal to kill the main thread produced by `self.run()`. This is triggered
    /// when the server receives a new connection. When the thread receives the
    /// signal off this channel, it will gracefully shutdown.
@@ -99,6 +102,7 @@ impl Runner {
            cgroup: None,
            dispatcher,
            counter: 1, // NB: must be odd, see the comment about the field for more.
+            last_upscale_request_at: None,
            kill,
        };

@@ -253,12 +257,11 @@ impl Runner {
                new_cgroup_mem_high = cgroup.config.calculate_memory_high_value(available_memory);
            }

-            let limits = MemoryLimits::new(
+            let limits = MemoryLimits {
                // new_cgroup_mem_high is initialized to 0 but it is guarancontextd to not be here
                // since it is properly initialized in the previous cgroup if let block
-                new_cgroup_mem_high,
-                available_memory,
-            );
+                high: new_cgroup_mem_high,
+            };
            cgroup
                .set_limits(&limits)
                .context("failed to set cgroup memory limits")?;
@@ -324,7 +327,9 @@ impl Runner {
                name = cgroup.path(),
                "updating cgroup memory.high",
            );
-            let limits = MemoryLimits::new(new_cgroup_mem_high, available_memory);
+            let limits = MemoryLimits {
+                high: new_cgroup_mem_high,
+            };
            cgroup
                .set_limits(&limits)
                .context("failed to set file cache size")?;
@@ -397,6 +402,20 @@ impl Runner {
                    if request.is_none() {
                        bail!("failed to listen for upscale event from cgroup")
                    }
+
+                    // If it's been less than 1 second since the last time we requested upscaling,
+                    // ignore the event, to avoid spamming the agent (otherwise, this can happen
+                    // ~1k times per second).
+                    if let Some(t) = self.last_upscale_request_at {
+                        let elapsed = t.elapsed();
+                        if elapsed < Duration::from_secs(1) {
+                            info!(elapsed_millis = elapsed.as_millis(), "cgroup asked for upscale but too soon to forward the request, ignoring");
+                            continue;
+                        }
+                    }
+
+                    self.last_upscale_request_at = Some(Instant::now());
+
                    info!("cgroup asking for upscale; forwarding request");
                    self.counter += 2; // Increment, preserving parity (i.e. keep the
                                       // counter odd). See the field comment for more.
--- a/pageserver/Cargo.toml
+++ b/pageserver/Cargo.toml
@@ -80,11 +80,11 @@ enum-map.workspace = true
 enumset.workspace = true
 strum.workspace = true
 strum_macros.workspace = true
+tempfile.workspace = true

 [dev-dependencies]
 criterion.workspace = true
 hex-literal.workspace = true
-tempfile.workspace = true
 tokio = { workspace = true, features = ["process", "sync", "fs", "rt", "io-util", "time", "test-util"] }

 [[bench]]
--- a/pageserver/ctl/src/layer_map_analyzer.rs
+++ b/pageserver/ctl/src/layer_map_analyzer.rs
@@ -3,6 +3,9 @@
 //! Currently it only analyzes holes, which are regions within the layer range that the layer contains no updates for. In the future it might do more analysis (maybe key quantiles?) but it should never return sensitive data.

 use anyhow::Result;
+use pageserver::context::{DownloadBehavior, RequestContext};
+use pageserver::task_mgr::TaskKind;
+use pageserver::tenant::{TENANTS_SEGMENT_NAME, TIMELINES_SEGMENT_NAME};
 use std::cmp::Ordering;
 use std::collections::BinaryHeap;
 use std::ops::Range;
@@ -95,9 +98,9 @@ pub(crate) fn parse_filename(name: &str) -> Option<LayerFile> {
 }

 // Finds the max_holes largest holes, ignoring any that are smaller than MIN_HOLE_LENGTH"
-async fn get_holes(path: &Path, max_holes: usize) -> Result<Vec<Hole>> {
-    let file = FileBlockReader::new(VirtualFile::open(path)?);
-    let summary_blk = file.read_blk(0).await?;
+async fn get_holes(path: &Path, max_holes: usize, ctx: &RequestContext) -> Result<Vec<Hole>> {
+    let file = FileBlockReader::new(VirtualFile::open(path).await?);
+    let summary_blk = file.read_blk(0, ctx).await?;
    let actual_summary = Summary::des_prefix(summary_blk.as_ref())?;
    let tree_reader = DiskBtreeReader::<_, DELTA_KEY_SIZE>::new(
        actual_summary.index_start_blk,
@@ -124,6 +127,7 @@ async fn get_holes(path: &Path, max_holes: usize) -> Result<Vec<Hole>> {
                prev_key = Some(curr.next());
                true
            },
+            ctx,
        )
        .await?;
    let mut holes = heap.into_vec();
@@ -134,6 +138,7 @@ async fn get_holes(path: &Path, max_holes: usize) -> Result<Vec<Hole>> {
 pub(crate) async fn main(cmd: &AnalyzeLayerMapCmd) -> Result<()> {
    let storage_path = &cmd.path;
    let max_holes = cmd.max_holes.unwrap_or(DEFAULT_MAX_HOLES);
+    let ctx = RequestContext::new(TaskKind::DebugTool, DownloadBehavior::Error);

    // Initialize virtual_file (file desriptor cache) and page cache which are needed to access layer persistent B-Tree.
    pageserver::virtual_file::init(10);
@@ -142,12 +147,12 @@ pub(crate) async fn main(cmd: &AnalyzeLayerMapCmd) -> Result<()> {
    let mut total_delta_layers = 0usize;
    let mut total_image_layers = 0usize;
    let mut total_excess_layers = 0usize;
-    for tenant in fs::read_dir(storage_path.join("tenants"))? {
+    for tenant in fs::read_dir(storage_path.join(TENANTS_SEGMENT_NAME))? {
        let tenant = tenant?;
        if !tenant.file_type()?.is_dir() {
            continue;
        }
-        for timeline in fs::read_dir(tenant.path().join("timelines"))? {
+        for timeline in fs::read_dir(tenant.path().join(TIMELINES_SEGMENT_NAME))? {
            let timeline = timeline?;
            if !timeline.file_type()?.is_dir() {
                continue;
@@ -162,7 +167,7 @@ pub(crate) async fn main(cmd: &AnalyzeLayerMapCmd) -> Result<()> {
                    parse_filename(&layer.file_name().into_string().unwrap())
                {
                    if layer_file.is_delta {
-                        layer_file.holes = get_holes(&layer.path(), max_holes).await?;
+                        layer_file.holes = get_holes(&layer.path(), max_holes, &ctx).await?;
                        n_deltas += 1;
                    }
                    layers.push(layer_file);
--- a/pageserver/ctl/src/layers.rs
+++ b/pageserver/ctl/src/layers.rs
@@ -2,9 +2,12 @@ use std::path::{Path, PathBuf};

 use anyhow::Result;
 use clap::Subcommand;
+use pageserver::context::{DownloadBehavior, RequestContext};
+use pageserver::task_mgr::TaskKind;
 use pageserver::tenant::block_io::BlockCursor;
 use pageserver::tenant::disk_btree::DiskBtreeReader;
 use pageserver::tenant::storage_layer::delta_layer::{BlobRef, Summary};
+use pageserver::tenant::{TENANTS_SEGMENT_NAME, TIMELINES_SEGMENT_NAME};
 use pageserver::{page_cache, virtual_file};
 use pageserver::{
    repository::{Key, KEY_SIZE},
@@ -43,12 +46,12 @@ pub(crate) enum LayerCmd {
    },
 }

-async fn read_delta_file(path: impl AsRef<Path>) -> Result<()> {
+async fn read_delta_file(path: impl AsRef<Path>, ctx: &RequestContext) -> Result<()> {
    let path = path.as_ref();
    virtual_file::init(10);
    page_cache::init(100);
-    let file = FileBlockReader::new(VirtualFile::open(path)?);
-    let summary_blk = file.read_blk(0).await?;
+    let file = FileBlockReader::new(VirtualFile::open(path).await?);
+    let summary_blk = file.read_blk(0, ctx).await?;
    let actual_summary = Summary::des_prefix(summary_blk.as_ref())?;
    let tree_reader = DiskBtreeReader::<_, DELTA_KEY_SIZE>::new(
        actual_summary.index_start_blk,
@@ -66,11 +69,12 @@ async fn read_delta_file(path: impl AsRef<Path>) -> Result<()> {
                all.push((curr, BlobRef(value_offset)));
                true
            },
+            ctx,
        )
        .await?;
-    let cursor = BlockCursor::new_fileblockreader_virtual(&file);
+    let cursor = BlockCursor::new_fileblockreader(&file);
    for (k, v) in all {
-        let value = cursor.read_blob(v.pos()).await?;
+        let value = cursor.read_blob(v.pos(), ctx).await?;
        println!("key:{} value_len:{}", k, value.len());
    }
    // TODO(chi): special handling for last key?
@@ -78,15 +82,16 @@ async fn read_delta_file(path: impl AsRef<Path>) -> Result<()> {
 }

 pub(crate) async fn main(cmd: &LayerCmd) -> Result<()> {
+    let ctx = RequestContext::new(TaskKind::DebugTool, DownloadBehavior::Error);
    match cmd {
        LayerCmd::List { path } => {
-            for tenant in fs::read_dir(path.join("tenants"))? {
+            for tenant in fs::read_dir(path.join(TENANTS_SEGMENT_NAME))? {
                let tenant = tenant?;
                if !tenant.file_type()?.is_dir() {
                    continue;
                }
                println!("tenant {}", tenant.file_name().to_string_lossy());
-                for timeline in fs::read_dir(tenant.path().join("timelines"))? {
+                for timeline in fs::read_dir(tenant.path().join(TIMELINES_SEGMENT_NAME))? {
                    let timeline = timeline?;
                    if !timeline.file_type()?.is_dir() {
                        continue;
@@ -101,9 +106,9 @@ pub(crate) async fn main(cmd: &LayerCmd) -> Result<()> {
            timeline,
        } => {
            let timeline_path = path
-                .join("tenants")
+                .join(TENANTS_SEGMENT_NAME)
                .join(tenant)
-                .join("timelines")
+                .join(TIMELINES_SEGMENT_NAME)
                .join(timeline);
            let mut idx = 0;
            for layer in fs::read_dir(timeline_path)? {
@@ -152,7 +157,7 @@ pub(crate) async fn main(cmd: &LayerCmd) -> Result<()> {
                        );

                        if layer_file.is_delta {
-                            read_delta_file(layer.path()).await?;
+                            read_delta_file(layer.path(), &ctx).await?;
                        } else {
                            anyhow::bail!("not supported yet :(");
                        }
--- a/pageserver/src/basebackup.rs
+++ b/pageserver/src/basebackup.rs
@@ -25,6 +25,7 @@ use crate::context::RequestContext;
 use crate::tenant::Timeline;
 use pageserver_api::reltag::{RelTag, SlruKind};

+use postgres_ffi::dispatch_pgversion;
 use postgres_ffi::pg_constants::{DEFAULTTABLESPACE_OID, GLOBALTABLESPACE_OID};
 use postgres_ffi::pg_constants::{PGDATA_SPECIAL_FILES, PGDATA_SUBDIRS, PG_HBA};
 use postgres_ffi::relfile_utils::{INIT_FORKNUM, MAIN_FORKNUM};
@@ -323,14 +324,25 @@ where
                .timeline
                .get_relmap_file(spcnode, dbnode, self.lsn, self.ctx)
                .await?;
-            ensure!(img.len() == 512);
+
+            ensure!(
+                img.len()
+                    == dispatch_pgversion!(
+                        self.timeline.pg_version,
+                        pgv::bindings::SIZEOF_RELMAPFILE
+                    )
+            );
+
            Some(img)
        } else {
            None
        };

        if spcnode == GLOBALTABLESPACE_OID {
-            let pg_version_str = self.timeline.pg_version.to_string();
+            let pg_version_str = match self.timeline.pg_version {
+                14 | 15 => self.timeline.pg_version.to_string(),
+                ver => format!("{ver}\x0A"),
+            };
            let header = new_tar_header("PG_VERSION", pg_version_str.len() as u64)?;
            self.ar.append(&header, pg_version_str.as_bytes()).await?;

@@ -374,7 +386,10 @@ where
            if let Some(img) = relmap_img {
                let dst_path = format!("base/{}/PG_VERSION", dbnode);

-                let pg_version_str = self.timeline.pg_version.to_string();
+                let pg_version_str = match self.timeline.pg_version {
+                    14 | 15 => self.timeline.pg_version.to_string(),
+                    ver => format!("{ver}\x0A"),
+                };
                let header = new_tar_header(&dst_path, pg_version_str.len() as u64)?;
                self.ar.append(&header, pg_version_str.as_bytes()).await?;

--- a/pageserver/src/bin/pageserver.rs
+++ b/pageserver/src/bin/pageserver.rs
@@ -388,6 +388,7 @@ fn start_pageserver(
            remote_storage: remote_storage.clone(),
        },
        order,
+        shutdown_pageserver.clone(),
    ))?;

    BACKGROUND_RUNTIME.spawn({
@@ -476,16 +477,19 @@ fn start_pageserver(
    {
        let _rt_guard = MGMT_REQUEST_RUNTIME.enter();

-        let router = http::make_router(
-            conf,
-            launch_ts,
-            http_auth,
-            broker_client.clone(),
-            remote_storage,
-            disk_usage_eviction_state,
-        )?
-        .build()
-        .map_err(|err| anyhow!(err))?;
+        let router_state = Arc::new(
+            http::routes::State::new(
+                conf,
+                http_auth.clone(),
+                remote_storage,
+                broker_client.clone(),
+                disk_usage_eviction_state,
+            )
+            .context("Failed to initialize router state")?,
+        );
+        let router = http::make_router(router_state, launch_ts, http_auth.clone())?
+            .build()
+            .map_err(|err| anyhow!(err))?;
        let service = utils::http::RouterService::new(router).unwrap();
        let server = hyper::Server::from_tcp(http_listener)?
            .serve(service)
@@ -514,6 +518,9 @@ fn start_pageserver(
            // creates a child context with the right DownloadBehavior.
            DownloadBehavior::Error,
        );
+
+        let local_disk_storage = conf.workdir.join("last_consumption_metrics.json");
+
        task_mgr::spawn(
            crate::BACKGROUND_RUNTIME.handle(),
            TaskKind::MetricsCollection,
@@ -540,6 +547,7 @@ fn start_pageserver(
                    conf.cached_metric_collection_interval,
                    conf.synthetic_size_calculation_interval,
                    conf.id,
+                    local_disk_storage,
                    metrics_ctx,
                )
                .instrument(info_span!("metrics_collection"))
--- a/pageserver/src/config.rs
+++ b/pageserver/src/config.rs
@@ -32,7 +32,8 @@ use crate::disk_usage_eviction_task::DiskUsageEvictionTaskConfig;
 use crate::tenant::config::TenantConf;
 use crate::tenant::config::TenantConfOpt;
 use crate::tenant::{
-    TENANT_ATTACHING_MARKER_FILENAME, TENANT_DELETED_MARKER_FILE_NAME, TIMELINES_SEGMENT_NAME,
+    TENANTS_SEGMENT_NAME, TENANT_ATTACHING_MARKER_FILENAME, TENANT_DELETED_MARKER_FILE_NAME,
+    TIMELINES_SEGMENT_NAME,
 };
 use crate::{
    IGNORED_TENANT_FILE_NAME, METADATA_FILE_NAME, TENANT_CONFIG_NAME, TIMELINE_DELETE_MARK_SUFFIX,
@@ -63,7 +64,7 @@ pub mod defaults {
        super::ConfigurableSemaphore::DEFAULT_INITIAL.get();

    pub const DEFAULT_METRIC_COLLECTION_INTERVAL: &str = "10 min";
-    pub const DEFAULT_CACHED_METRIC_COLLECTION_INTERVAL: &str = "1 hour";
+    pub const DEFAULT_CACHED_METRIC_COLLECTION_INTERVAL: &str = "0s";
    pub const DEFAULT_METRIC_COLLECTION_ENDPOINT: Option<reqwest::Url> = None;
    pub const DEFAULT_SYNTHETIC_SIZE_CALCULATION_INTERVAL: &str = "10 min";
    pub const DEFAULT_BACKGROUND_TASK_MAXIMUM_DELAY: &str = "10s";
@@ -72,7 +73,7 @@ pub mod defaults {
    /// Default built-in configuration file.
    ///
    pub const DEFAULT_CONFIG_FILE: &str = formatcp!(
-        r###"
+        r#"
 # Initial configuration file created by 'pageserver --init'
 #listen_pg_addr = '{DEFAULT_PG_LISTEN_ADDR}'
 #listen_http_addr = '{DEFAULT_HTTP_LISTEN_ADDR}'
@@ -117,7 +118,7 @@ pub mod defaults {

 [remote_storage]

-"###
+"#
    );
 }

@@ -204,6 +205,8 @@ pub struct PageServerConf {
    /// has it's initial logical size calculated. Not running background tasks for some seconds is
    /// not terrible.
    pub background_task_maximum_delay: Duration,
+
+    pub control_plane_api: Option<Url>,
 }

 /// We do not want to store this in a PageServerConf because the latter may be logged
@@ -278,6 +281,8 @@ struct PageServerConfigBuilder {
    ondemand_download_behavior_treat_error_as_warn: BuilderValue<bool>,

    background_task_maximum_delay: BuilderValue<Duration>,
+
+    control_plane_api: BuilderValue<Option<Url>>,
 }

 impl Default for PageServerConfigBuilder {
@@ -340,6 +345,8 @@ impl Default for PageServerConfigBuilder {
                DEFAULT_BACKGROUND_TASK_MAXIMUM_DELAY,
            )
            .unwrap()),
+
+            control_plane_api: Set(None),
        }
    }
 }
@@ -468,6 +475,10 @@ impl PageServerConfigBuilder {
        self.background_task_maximum_delay = BuilderValue::Set(delay);
    }

+    pub fn control_plane_api(&mut self, api: Url) {
+        self.control_plane_api = BuilderValue::Set(Some(api))
+    }
+
    pub fn build(self) -> anyhow::Result<PageServerConf> {
        let concurrent_tenant_size_logical_size_queries = self
            .concurrent_tenant_size_logical_size_queries
@@ -553,6 +564,9 @@ impl PageServerConfigBuilder {
            background_task_maximum_delay: self
                .background_task_maximum_delay
                .ok_or(anyhow!("missing background_task_maximum_delay"))?,
+            control_plane_api: self
+                .control_plane_api
+                .ok_or(anyhow!("missing control_plane_api"))?,
        })
    }
 }
@@ -563,7 +577,7 @@ impl PageServerConf {
    //

    pub fn tenants_path(&self) -> PathBuf {
-        self.workdir.join("tenants")
+        self.workdir.join(TENANTS_SEGMENT_NAME)
    }

    pub fn tenant_path(&self, tenant_id: &TenantId) -> PathBuf {
@@ -643,23 +657,6 @@ impl PageServerConf {
            .join(METADATA_FILE_NAME)
    }

-    /// Files on the remote storage are stored with paths, relative to the workdir.
-    /// That path includes in itself both tenant and timeline ids, allowing to have a unique remote storage path.
-    ///
-    /// Errors if the path provided does not start from pageserver's workdir.
-    pub fn remote_path(&self, local_path: &Path) -> anyhow::Result<RemotePath> {
-        local_path
-            .strip_prefix(&self.workdir)
-            .context("Failed to strip workdir prefix")
-            .and_then(RemotePath::new)
-            .with_context(|| {
-                format!(
-                    "Failed to resolve remote part of path {:?} for base {:?}",
-                    local_path, self.workdir
-                )
-            })
-    }
-
    /// Turns storage remote path of a file into its local path.
    pub fn local_path(&self, remote_path: &RemotePath) -> PathBuf {
        remote_path.with_base(&self.workdir)
@@ -671,26 +668,18 @@ impl PageServerConf {
    pub fn pg_distrib_dir(&self, pg_version: u32) -> anyhow::Result<PathBuf> {
        let path = self.pg_distrib_dir.clone();

+        #[allow(clippy::manual_range_patterns)]
        match pg_version {
-            14 => Ok(path.join(format!("v{pg_version}"))),
-            15 => Ok(path.join(format!("v{pg_version}"))),
+            14 | 15 | 16 => Ok(path.join(format!("v{pg_version}"))),
            _ => bail!("Unsupported postgres version: {}", pg_version),
        }
    }

    pub fn pg_bin_dir(&self, pg_version: u32) -> anyhow::Result<PathBuf> {
-        match pg_version {
-            14 => Ok(self.pg_distrib_dir(pg_version)?.join("bin")),
-            15 => Ok(self.pg_distrib_dir(pg_version)?.join("bin")),
-            _ => bail!("Unsupported postgres version: {}", pg_version),
-        }
+        Ok(self.pg_distrib_dir(pg_version)?.join("bin"))
    }
    pub fn pg_lib_dir(&self, pg_version: u32) -> anyhow::Result<PathBuf> {
-        match pg_version {
-            14 => Ok(self.pg_distrib_dir(pg_version)?.join("lib")),
-            15 => Ok(self.pg_distrib_dir(pg_version)?.join("lib")),
-            _ => bail!("Unsupported postgres version: {}", pg_version),
-        }
+        Ok(self.pg_distrib_dir(pg_version)?.join("lib"))
    }

    /// Parse a configuration file (pageserver.toml) into a PageServerConf struct,
@@ -758,6 +747,7 @@ impl PageServerConf {
                },
                "ondemand_download_behavior_treat_error_as_warn" => builder.ondemand_download_behavior_treat_error_as_warn(parse_toml_bool(key, item)?),
                "background_task_maximum_delay" => builder.background_task_maximum_delay(parse_toml_duration(key, item)?),
+                "control_plane_api" => builder.control_plane_api(parse_toml_string(key, item)?.parse().context("failed to parse control plane URL")?),
                _ => bail!("unrecognized pageserver option '{key}'"),
            }
        }
@@ -926,6 +916,7 @@ impl PageServerConf {
            test_remote_failures: 0,
            ondemand_download_behavior_treat_error_as_warn: false,
            background_task_maximum_delay: Duration::ZERO,
+            control_plane_api: None,
        }
    }
 }
@@ -1149,6 +1140,7 @@ background_task_maximum_delay = '334 s'
                background_task_maximum_delay: humantime::parse_duration(
                    defaults::DEFAULT_BACKGROUND_TASK_MAXIMUM_DELAY
                )?,
+                control_plane_api: None
            },
            "Correct defaults should be used when no config values are provided"
        );
@@ -1204,6 +1196,7 @@ background_task_maximum_delay = '334 s'
                test_remote_failures: 0,
                ondemand_download_behavior_treat_error_as_warn: false,
                background_task_maximum_delay: Duration::from_secs(334),
+                control_plane_api: None
            },
            "Should be able to parse all basic config values correctly"
        );
--- a/pageserver/src/consumption_metrics.rs
+++ b/pageserver/src/consumption_metrics.rs
@@ -1,188 +1,54 @@
-//!
 //! Periodically collect consumption metrics for all active tenants
 //! and push them to a HTTP endpoint.
-//! Cache metrics to send only the updated ones.
-//!
 use crate::context::{DownloadBehavior, RequestContext};
 use crate::task_mgr::{self, TaskKind, BACKGROUND_RUNTIME};
 use crate::tenant::{mgr, LogicalSizeCalculationCause};
-use anyhow;
-use chrono::{DateTime, Utc};
-use consumption_metrics::{idempotency_key, Event, EventChunk, EventType, CHUNK_SIZE};
+use consumption_metrics::EventType;
 use pageserver_api::models::TenantState;
 use reqwest::Url;
-use serde::Serialize;
-use serde_with::{serde_as, DisplayFromStr};
 use std::collections::HashMap;
+use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::{Duration, SystemTime};
 use tracing::*;
-use utils::id::{NodeId, TenantId, TimelineId};
-use utils::lsn::Lsn;
+use utils::id::NodeId;
+
+mod metrics;
+use metrics::MetricsKey;
+mod disk_cache;
+mod upload;

 const DEFAULT_HTTP_REPORTING_TIMEOUT: Duration = Duration::from_secs(60);

-#[serde_as]
-#[derive(Serialize, Debug, Clone, Copy)]
-struct Ids {
-    #[serde_as(as = "DisplayFromStr")]
-    tenant_id: TenantId,
-    #[serde_as(as = "Option<DisplayFromStr>")]
-    #[serde(skip_serializing_if = "Option::is_none")]
-    timeline_id: Option<TimelineId>,
-}
+/// Basically a key-value pair, but usually in a Vec except for [`Cache`].
+///
+/// This is as opposed to `consumption_metrics::Event` which is the externally communicated form.
+/// Difference is basically the missing idempotency key, which lives only for the duration of
+/// upload attempts.
+type RawMetric = (MetricsKey, (EventType, u64));

-/// Key that uniquely identifies the object, this metric describes.
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-struct MetricsKey {
-    tenant_id: TenantId,
-    timeline_id: Option<TimelineId>,
-    metric: &'static str,
-}
-
-impl MetricsKey {
-    const fn absolute_values(self) -> AbsoluteValueFactory {
-        AbsoluteValueFactory(self)
-    }
-    const fn incremental_values(self) -> IncrementalValueFactory {
-        IncrementalValueFactory(self)
-    }
-}
-
-/// Helper type which each individual metric kind can return to produce only absolute values.
-struct AbsoluteValueFactory(MetricsKey);
-
-impl AbsoluteValueFactory {
-    fn at(self, time: DateTime<Utc>, val: u64) -> (MetricsKey, (EventType, u64)) {
-        let key = self.0;
-        (key, (EventType::Absolute { time }, val))
-    }
-}
-
-/// Helper type which each individual metric kind can return to produce only incremental values.
-struct IncrementalValueFactory(MetricsKey);
-
-impl IncrementalValueFactory {
-    #[allow(clippy::wrong_self_convention)]
-    fn from_previous_up_to(
-        self,
-        prev_end: DateTime<Utc>,
-        up_to: DateTime<Utc>,
-        val: u64,
-    ) -> (MetricsKey, (EventType, u64)) {
-        let key = self.0;
-        // cannot assert prev_end < up_to because these are realtime clock based
-        (
-            key,
-            (
-                EventType::Incremental {
-                    start_time: prev_end,
-                    stop_time: up_to,
-                },
-                val,
-            ),
-        )
-    }
-
-    fn key(&self) -> &MetricsKey {
-        &self.0
-    }
-}
-
-// the static part of a MetricsKey
-impl MetricsKey {
-    /// Absolute value of [`Timeline::get_last_record_lsn`].
-    ///
-    /// [`Timeline::get_last_record_lsn`]: crate::tenant::Timeline::get_last_record_lsn
-    const fn written_size(tenant_id: TenantId, timeline_id: TimelineId) -> AbsoluteValueFactory {
-        MetricsKey {
-            tenant_id,
-            timeline_id: Some(timeline_id),
-            metric: "written_size",
-        }
-        .absolute_values()
-    }
-
-    /// Values will be the difference of the latest [`MetricsKey::written_size`] to what we
-    /// previously sent, starting from the previously sent incremental time range ending at the
-    /// latest absolute measurement.
-    const fn written_size_delta(
-        tenant_id: TenantId,
-        timeline_id: TimelineId,
-    ) -> IncrementalValueFactory {
-        MetricsKey {
-            tenant_id,
-            timeline_id: Some(timeline_id),
-            // the name here is correctly about data not size, because that is what is wanted by
-            // downstream pipeline
-            metric: "written_data_bytes_delta",
-        }
-        .incremental_values()
-    }
-
-    /// Exact [`Timeline::get_current_logical_size`].
-    ///
-    /// [`Timeline::get_current_logical_size`]: crate::tenant::Timeline::get_current_logical_size
-    const fn timeline_logical_size(
-        tenant_id: TenantId,
-        timeline_id: TimelineId,
-    ) -> AbsoluteValueFactory {
-        MetricsKey {
-            tenant_id,
-            timeline_id: Some(timeline_id),
-            metric: "timeline_logical_size",
-        }
-        .absolute_values()
-    }
-
-    /// [`Tenant::remote_size`]
-    ///
-    /// [`Tenant::remote_size`]: crate::tenant::Tenant::remote_size
-    const fn remote_storage_size(tenant_id: TenantId) -> AbsoluteValueFactory {
-        MetricsKey {
-            tenant_id,
-            timeline_id: None,
-            metric: "remote_storage_size",
-        }
-        .absolute_values()
-    }
-
-    /// Sum of [`Timeline::resident_physical_size`] for each `Tenant`.
-    ///
-    /// [`Timeline::resident_physical_size`]: crate::tenant::Timeline::resident_physical_size
-    const fn resident_size(tenant_id: TenantId) -> AbsoluteValueFactory {
-        MetricsKey {
-            tenant_id,
-            timeline_id: None,
-            metric: "resident_size",
-        }
-        .absolute_values()
-    }
-
-    /// [`Tenant::cached_synthetic_size`] as refreshed by [`calculate_synthetic_size_worker`].
-    ///
-    /// [`Tenant::cached_synthetic_size`]: crate::tenant::Tenant::cached_synthetic_size
-    const fn synthetic_size(tenant_id: TenantId) -> AbsoluteValueFactory {
-        MetricsKey {
-            tenant_id,
-            timeline_id: None,
-            metric: "synthetic_storage_size",
-        }
-        .absolute_values()
-    }
-}
+/// Caches the [`RawMetric`]s
+///
+/// In practice, during startup, last sent values are stored here to be used in calculating new
+/// ones. After successful uploading, the cached values are updated to cache. This used to be used
+/// for deduplication, but that is no longer needed.
+type Cache = HashMap<MetricsKey, (EventType, u64)>;

 /// Main thread that serves metrics collection
 pub async fn collect_metrics(
    metric_collection_endpoint: &Url,
    metric_collection_interval: Duration,
-    cached_metric_collection_interval: Duration,
+    _cached_metric_collection_interval: Duration,
    synthetic_size_calculation_interval: Duration,
    node_id: NodeId,
+    local_disk_storage: PathBuf,
    ctx: RequestContext,
 ) -> anyhow::Result<()> {
-    let mut ticker = tokio::time::interval(metric_collection_interval);
-    info!("starting collect_metrics");
+    if _cached_metric_collection_interval != Duration::ZERO {
+        tracing::warn!(
+            "cached_metric_collection_interval is no longer used, please set it to zero."
+        )
+    }

    // spin up background worker that caclulates tenant sizes
    let worker_ctx =
@@ -202,543 +68,216 @@ pub async fn collect_metrics(
        },
    );

+    let path: Arc<PathBuf> = Arc::new(local_disk_storage);
+
+    let cancel = task_mgr::shutdown_token();
+
+    let restore_and_reschedule = restore_and_reschedule(&path, metric_collection_interval);
+
+    let mut cached_metrics = tokio::select! {
+        _ = cancel.cancelled() => return Ok(()),
+        ret = restore_and_reschedule => ret,
+    };
+
    // define client here to reuse it for all requests
    let client = reqwest::ClientBuilder::new()
        .timeout(DEFAULT_HTTP_REPORTING_TIMEOUT)
        .build()
        .expect("Failed to create http client with timeout");
-    let mut cached_metrics = HashMap::new();
-    let mut prev_iteration_time: std::time::Instant = std::time::Instant::now();
-
-    loop {
-        tokio::select! {
-            _ = task_mgr::shutdown_watcher() => {
-                info!("collect_metrics received cancellation request");
-                return Ok(());
-            },
-            tick_at = ticker.tick() => {
-
-                // send cached metrics every cached_metric_collection_interval
-                let send_cached = prev_iteration_time.elapsed() >= cached_metric_collection_interval;
-
-                if send_cached {
-                    prev_iteration_time = std::time::Instant::now();
-                }
-
-                collect_metrics_iteration(&client, &mut cached_metrics, metric_collection_endpoint, node_id, &ctx, send_cached).await;
-
-                crate::tenant::tasks::warn_when_period_overrun(
-                    tick_at.elapsed(),
-                    metric_collection_interval,
-                    "consumption_metrics_collect_metrics",
-                );
-            }
-        }
-    }
-}
-
-/// One iteration of metrics collection
-///
-/// Gather per-tenant and per-timeline metrics and send them to the `metric_collection_endpoint`.
-/// Cache metrics to avoid sending the same metrics multiple times.
-///
-/// This function handles all errors internally
-/// and doesn't break iteration if just one tenant fails.
-///
-/// TODO
-/// - refactor this function (chunking+sending part) to reuse it in proxy module;
-async fn collect_metrics_iteration(
-    client: &reqwest::Client,
-    cached_metrics: &mut HashMap<MetricsKey, (EventType, u64)>,
-    metric_collection_endpoint: &reqwest::Url,
-    node_id: NodeId,
-    ctx: &RequestContext,
-    send_cached: bool,
-) {
-    let mut current_metrics: Vec<(MetricsKey, (EventType, u64))> = Vec::new();
-    trace!(
-        "starting collect_metrics_iteration. metric_collection_endpoint: {}",
-        metric_collection_endpoint
-    );
-
-    // get list of tenants
-    let tenants = match mgr::list_tenants().await {
-        Ok(tenants) => tenants,
-        Err(err) => {
-            error!("failed to list tenants: {:?}", err);
-            return;
-        }
-    };
-
-    // iterate through list of Active tenants and collect metrics
-    for (tenant_id, tenant_state) in tenants {
-        if tenant_state != TenantState::Active {
-            continue;
-        }
-
-        let tenant = match mgr::get_tenant(tenant_id, true).await {
-            Ok(tenant) => tenant,
-            Err(err) => {
-                // It is possible that tenant was deleted between
-                // `list_tenants` and `get_tenant`, so just warn about it.
-                warn!("failed to get tenant {tenant_id:?}: {err:?}");
-                continue;
-            }
-        };
-
-        let mut tenant_resident_size = 0;
-
-        // iterate through list of timelines in tenant
-        for timeline in tenant.list_timelines() {
-            // collect per-timeline metrics only for active timelines
-
-            let timeline_id = timeline.timeline_id;
-
-            match TimelineSnapshot::collect(&timeline, ctx) {
-                Ok(Some(snap)) => {
-                    snap.to_metrics(
-                        tenant_id,
-                        timeline_id,
-                        Utc::now(),
-                        &mut current_metrics,
-                        cached_metrics,
-                    );
-                }
-                Ok(None) => {}
-                Err(e) => {
-                    error!(
-                        "failed to get metrics values for tenant {tenant_id} timeline {}: {e:#?}",
-                        timeline.timeline_id
-                    );
-                    continue;
-                }
-            }
-
-            tenant_resident_size += timeline.resident_physical_size();
-        }
-
-        current_metrics
-            .push(MetricsKey::remote_storage_size(tenant_id).at(Utc::now(), tenant.remote_size()));
-
-        current_metrics
-            .push(MetricsKey::resident_size(tenant_id).at(Utc::now(), tenant_resident_size));
-
-        // Note that this metric is calculated in a separate bgworker
-        // Here we only use cached value, which may lag behind the real latest one
-        let synthetic_size = tenant.cached_synthetic_size();
-
-        if synthetic_size != 0 {
-            // only send non-zeroes because otherwise these show up as errors in logs
-            current_metrics
-                .push(MetricsKey::synthetic_size(tenant_id).at(Utc::now(), synthetic_size));
-        }
-    }
-
-    // Filter metrics, unless we want to send all metrics, including cached ones.
-    // See: https://github.com/neondatabase/neon/issues/3485
-    if !send_cached {
-        current_metrics.retain(|(curr_key, (kind, curr_val))| {
-            if kind.is_incremental() {
-                // incremental values (currently only written_size_delta) should not get any cache
-                // deduplication because they will be used by upstream for "is still alive."
-                true
-            } else {
-                match cached_metrics.get(curr_key) {
-                    Some((_, val)) => val != curr_val,
-                    None => true,
-                }
-            }
-        });
-    }
-
-    if current_metrics.is_empty() {
-        trace!("no new metrics to send");
-        return;
-    }
-
-    // Send metrics.
-    // Split into chunks of 1000 metrics to avoid exceeding the max request size
-    let chunks = current_metrics.chunks(CHUNK_SIZE);
-
-    let mut chunk_to_send: Vec<Event<Ids>> = Vec::with_capacity(CHUNK_SIZE);

    let node_id = node_id.to_string();

-    for chunk in chunks {
-        chunk_to_send.clear();
+    // reminder: ticker is ready immediatedly
+    let mut ticker = tokio::time::interval(metric_collection_interval);

-        // enrich metrics with type,timestamp and idempotency key before sending
-        chunk_to_send.extend(chunk.iter().map(|(curr_key, (when, curr_val))| Event {
-            kind: *when,
-            metric: curr_key.metric,
-            idempotency_key: idempotency_key(&node_id),
-            value: *curr_val,
-            extra: Ids {
-                tenant_id: curr_key.tenant_id,
-                timeline_id: curr_key.timeline_id,
-            },
-        }));
+    loop {
+        let tick_at = tokio::select! {
+            _ = cancel.cancelled() => return Ok(()),
+            tick_at = ticker.tick() => tick_at,
+        };

-        const MAX_RETRIES: u32 = 3;
+        // these are point in time, with variable "now"
+        let metrics = metrics::collect_all_metrics(&cached_metrics, &ctx).await;

-        for attempt in 0..MAX_RETRIES {
-            let res = client
-                .post(metric_collection_endpoint.clone())
-                .json(&EventChunk {
-                    events: (&chunk_to_send).into(),
-                })
-                .send()
-                .await;
+        if metrics.is_empty() {
+            continue;
+        }

-            match res {
-                Ok(res) => {
-                    if res.status().is_success() {
-                        // update cached metrics after they were sent successfully
-                        for (curr_key, curr_val) in chunk.iter() {
-                            cached_metrics.insert(curr_key.clone(), *curr_val);
-                        }
-                    } else {
-                        error!("metrics endpoint refused the sent metrics: {:?}", res);
-                        for metric in chunk_to_send
-                            .iter()
-                            .filter(|metric| metric.value > (1u64 << 40))
-                        {
-                            // Report if the metric value is suspiciously large
-                            error!("potentially abnormal metric value: {:?}", metric);
-                        }
-                    }
-                    break;
+        let metrics = Arc::new(metrics);
+
+        // why not race cancellation here? because we are one of the last tasks, and if we are
+        // already here, better to try to flush the new values.
+
+        let flush = async {
+            match disk_cache::flush_metrics_to_disk(&metrics, &path).await {
+                Ok(()) => {
+                    tracing::debug!("flushed metrics to disk");
                }
-                Err(err) if err.is_timeout() => {
-                    error!(attempt, "timeout sending metrics, retrying immediately");
-                    continue;
-                }
-                Err(err) => {
-                    error!(attempt, ?err, "failed to send metrics");
-                    break;
+                Err(e) => {
+                    // idea here is that if someone creates a directory as our path, then they
+                    // might notice it from the logs before shutdown and remove it
+                    tracing::error!("failed to persist metrics to {path:?}: {e:#}");
                }
            }
+        };
+
+        let upload = async {
+            let res = upload::upload_metrics(
+                &client,
+                metric_collection_endpoint,
+                &cancel,
+                &node_id,
+                &metrics,
+                &mut cached_metrics,
+            )
+            .await;
+            if let Err(e) = res {
+                // serialization error which should never happen
+                tracing::error!("failed to upload due to {e:#}");
+            }
+        };
+
+        // let these run concurrently
+        let (_, _) = tokio::join!(flush, upload);
+
+        crate::tenant::tasks::warn_when_period_overrun(
+            tick_at.elapsed(),
+            metric_collection_interval,
+            "consumption_metrics_collect_metrics",
+        );
+    }
+}
+
+/// Called on the first iteration in an attempt to join the metric uploading schedule from previous
+/// pageserver session. Pageserver is supposed to upload at intervals regardless of restarts.
+///
+/// Cancellation safe.
+async fn restore_and_reschedule(
+    path: &Arc<PathBuf>,
+    metric_collection_interval: Duration,
+) -> Cache {
+    let (cached, earlier_metric_at) = match disk_cache::read_metrics_from_disk(path.clone()).await {
+        Ok(found_some) => {
+            // there is no min needed because we write these sequentially in
+            // collect_all_metrics
+            let earlier_metric_at = found_some
+                .iter()
+                .map(|(_, (et, _))| et.recorded_at())
+                .copied()
+                .next();
+
+            let cached = found_some.into_iter().collect::<Cache>();
+
+            (cached, earlier_metric_at)
+        }
+        Err(e) => {
+            use std::io::{Error, ErrorKind};
+
+            let root = e.root_cause();
+            let maybe_ioerr = root.downcast_ref::<Error>();
+            let is_not_found = maybe_ioerr.is_some_and(|e| e.kind() == ErrorKind::NotFound);
+
+            if !is_not_found {
+                tracing::info!("failed to read any previous metrics from {path:?}: {e:#}");
+            }
+
+            (HashMap::new(), None)
+        }
+    };
+
+    if let Some(earlier_metric_at) = earlier_metric_at {
+        let earlier_metric_at: SystemTime = earlier_metric_at.into();
+
+        let error = reschedule(earlier_metric_at, metric_collection_interval).await;
+
+        if let Some(error) = error {
+            if error.as_secs() >= 60 {
+                tracing::info!(
+                    error_ms = error.as_millis(),
+                    "startup scheduling error due to restart"
+                )
+            }
        }
    }
+
+    cached
 }

-/// Internal type to make timeline metric production testable.
-///
-/// As this value type contains all of the information needed from a timeline to produce the
-/// metrics, it can easily be created with different values in test.
-struct TimelineSnapshot {
-    loaded_at: (Lsn, SystemTime),
-    last_record_lsn: Lsn,
-    current_exact_logical_size: Option<u64>,
-}
+async fn reschedule(
+    earlier_metric_at: SystemTime,
+    metric_collection_interval: Duration,
+) -> Option<Duration> {
+    let now = SystemTime::now();
+    match now.duration_since(earlier_metric_at) {
+        Ok(from_last_send) if from_last_send < metric_collection_interval => {
+            let sleep_for = metric_collection_interval - from_last_send;

-impl TimelineSnapshot {
-    /// Collect the metrics from an actual timeline.
-    ///
-    /// Fails currently only when [`Timeline::get_current_logical_size`] fails.
-    ///
-    /// [`Timeline::get_current_logical_size`]: crate::tenant::Timeline::get_current_logical_size
-    fn collect(
-        t: &Arc<crate::tenant::Timeline>,
-        ctx: &RequestContext,
-    ) -> anyhow::Result<Option<Self>> {
-        use anyhow::Context;
+            let deadline = std::time::Instant::now() + sleep_for;

-        if !t.is_active() {
-            // no collection for broken or stopping needed, we will still keep the cached values
-            // though at the caller.
-            Ok(None)
-        } else {
-            let loaded_at = t.loaded_at;
-            let last_record_lsn = t.get_last_record_lsn();
+            tokio::time::sleep_until(deadline.into()).await;

-            let current_exact_logical_size = {
-                let span = info_span!("collect_metrics_iteration", tenant_id = %t.tenant_id, timeline_id = %t.timeline_id);
-                let res = span
-                    .in_scope(|| t.get_current_logical_size(ctx))
-                    .context("get_current_logical_size");
-                match res? {
-                    // Only send timeline logical size when it is fully calculated.
-                    (size, is_exact) if is_exact => Some(size),
-                    (_, _) => None,
-                }
-            };
+            let now = std::time::Instant::now();

-            Ok(Some(TimelineSnapshot {
-                loaded_at,
-                last_record_lsn,
-                current_exact_logical_size,
-            }))
-        }
-    }
-
-    /// Produce the timeline consumption metrics into the `metrics` argument.
-    fn to_metrics(
-        &self,
-        tenant_id: TenantId,
-        timeline_id: TimelineId,
-        now: DateTime<Utc>,
-        metrics: &mut Vec<(MetricsKey, (EventType, u64))>,
-        cache: &HashMap<MetricsKey, (EventType, u64)>,
-    ) {
-        let timeline_written_size = u64::from(self.last_record_lsn);
-
-        let (key, written_size_now) =
-            MetricsKey::written_size(tenant_id, timeline_id).at(now, timeline_written_size);
-
-        // last_record_lsn can only go up, right now at least, TODO: #2592 or related
-        // features might change this.
-
-        let written_size_delta_key = MetricsKey::written_size_delta(tenant_id, timeline_id);
-
-        // use this when available, because in a stream of incremental values, it will be
-        // accurate where as when last_record_lsn stops moving, we will only cache the last
-        // one of those.
-        let last_stop_time = cache
-            .get(written_size_delta_key.key())
-            .map(|(until, _val)| {
-                until
-                    .incremental_timerange()
-                    .expect("never create EventType::Absolute for written_size_delta")
-                    .end
-            });
-
-        // by default, use the last sent written_size as the basis for
-        // calculating the delta. if we don't yet have one, use the load time value.
-        let prev = cache
-            .get(&key)
-            .map(|(prev_at, prev)| {
-                // use the prev time from our last incremental update, or default to latest
-                // absolute update on the first round.
-                let prev_at = prev_at
-                    .absolute_time()
-                    .expect("never create EventType::Incremental for written_size");
-                let prev_at = last_stop_time.unwrap_or(prev_at);
-                (*prev_at, *prev)
-            })
-            .unwrap_or_else(|| {
-                // if we don't have a previous point of comparison, compare to the load time
-                // lsn.
-                let (disk_consistent_lsn, loaded_at) = &self.loaded_at;
-                (DateTime::from(*loaded_at), disk_consistent_lsn.0)
-            });
-
-        // written_size_bytes_delta
-        metrics.extend(
-            if let Some(delta) = written_size_now.1.checked_sub(prev.1) {
-                let up_to = written_size_now
-                    .0
-                    .absolute_time()
-                    .expect("never create EventType::Incremental for written_size");
-                let key_value = written_size_delta_key.from_previous_up_to(prev.0, *up_to, delta);
-                Some(key_value)
+            // executor threads might be busy, add extra measurements
+            Some(if now < deadline {
+                deadline - now
            } else {
-                None
-            },
-        );
-
-        // written_size
-        metrics.push((key, written_size_now));
-
-        if let Some(size) = self.current_exact_logical_size {
-            metrics.push(MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, size));
+                now - deadline
+            })
+        }
+        Ok(from_last_send) => Some(from_last_send.saturating_sub(metric_collection_interval)),
+        Err(_) => {
+            tracing::warn!(
+                ?now,
+                ?earlier_metric_at,
+                "oldest recorded metric is in future; first values will come out with inconsistent timestamps"
+            );
+            earlier_metric_at.duration_since(now).ok()
        }
    }
 }

 /// Caclculate synthetic size for each active tenant
-pub async fn calculate_synthetic_size_worker(
+async fn calculate_synthetic_size_worker(
    synthetic_size_calculation_interval: Duration,
    ctx: &RequestContext,
 ) -> anyhow::Result<()> {
    info!("starting calculate_synthetic_size_worker");

+    // reminder: ticker is ready immediatedly
    let mut ticker = tokio::time::interval(synthetic_size_calculation_interval);
+    let cause = LogicalSizeCalculationCause::ConsumptionMetricsSyntheticSize;

    loop {
-        tokio::select! {
-            _ = task_mgr::shutdown_watcher() => {
-                return Ok(());
-            },
-            tick_at = ticker.tick() => {
+        let tick_at = tokio::select! {
+            _ = task_mgr::shutdown_watcher() => return Ok(()),
+            tick_at = ticker.tick() => tick_at,
+        };

-                let tenants = match mgr::list_tenants().await {
-                    Ok(tenants) => tenants,
-                    Err(e) => {
-                        warn!("cannot get tenant list: {e:#}");
-                        continue;
-                    }
-                };
-                // iterate through list of Active tenants and collect metrics
-                for (tenant_id, tenant_state) in tenants {
+        let tenants = match mgr::list_tenants().await {
+            Ok(tenants) => tenants,
+            Err(e) => {
+                warn!("cannot get tenant list: {e:#}");
+                continue;
+            }
+        };

-                    if tenant_state != TenantState::Active {
-                        continue;
-                    }
-
-                    if let Ok(tenant) = mgr::get_tenant(tenant_id, true).await
-                    {
-                        if let Err(e) = tenant.calculate_synthetic_size(
-                            LogicalSizeCalculationCause::ConsumptionMetricsSyntheticSize,
-                            ctx).await {
-                            error!("failed to calculate synthetic size for tenant {}: {}", tenant_id, e);
-                        }
-                    }
+        for (tenant_id, tenant_state) in tenants {
+            if tenant_state != TenantState::Active {
+                continue;
+            }

+            if let Ok(tenant) = mgr::get_tenant(tenant_id, true).await {
+                if let Err(e) = tenant.calculate_synthetic_size(cause, ctx).await {
+                    error!("failed to calculate synthetic size for tenant {tenant_id}: {e:#}");
                }
-
-                crate::tenant::tasks::warn_when_period_overrun(
-                    tick_at.elapsed(),
-                    synthetic_size_calculation_interval,
-                    "consumption_metrics_synthetic_size_worker",
-                );
            }
        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use std::collections::HashMap;
-
-    use std::time::SystemTime;
-    use utils::{
-        id::{TenantId, TimelineId},
-        lsn::Lsn,
-    };
-
-    use crate::consumption_metrics::MetricsKey;
-
-    use super::TimelineSnapshot;
-    use chrono::{DateTime, Utc};
-
-    #[test]
-    fn startup_collected_timeline_metrics_before_advancing() {
-        let tenant_id = TenantId::generate();
-        let timeline_id = TimelineId::generate();
-
-        let mut metrics = Vec::new();
-        let cache = HashMap::new();
-
-        let initdb_lsn = Lsn(0x10000);
-        let disk_consistent_lsn = Lsn(initdb_lsn.0 * 2);
-
-        let snap = TimelineSnapshot {
-            loaded_at: (disk_consistent_lsn, SystemTime::now()),
-            last_record_lsn: disk_consistent_lsn,
-            current_exact_logical_size: Some(0x42000),
-        };
-
-        let now = DateTime::<Utc>::from(SystemTime::now());
-
-        snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
-
-        assert_eq!(
-            metrics,
-            &[
-                MetricsKey::written_size_delta(tenant_id, timeline_id).from_previous_up_to(
-                    snap.loaded_at.1.into(),
-                    now,
-                    0
-                ),
-                MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
-                MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
-            ]
-        );
-    }
-
-    #[test]
-    fn startup_collected_timeline_metrics_second_round() {
-        let tenant_id = TenantId::generate();
-        let timeline_id = TimelineId::generate();
-
-        let [now, before, init] = time_backwards();
-
-        let now = DateTime::<Utc>::from(now);
-        let before = DateTime::<Utc>::from(before);
-
-        let initdb_lsn = Lsn(0x10000);
-        let disk_consistent_lsn = Lsn(initdb_lsn.0 * 2);
-
-        let mut metrics = Vec::new();
-        let cache = HashMap::from([
-            MetricsKey::written_size(tenant_id, timeline_id).at(before, disk_consistent_lsn.0)
-        ]);
-
-        let snap = TimelineSnapshot {
-            loaded_at: (disk_consistent_lsn, init),
-            last_record_lsn: disk_consistent_lsn,
-            current_exact_logical_size: Some(0x42000),
-        };
-
-        snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
-
-        assert_eq!(
-            metrics,
-            &[
-                MetricsKey::written_size_delta(tenant_id, timeline_id)
-                    .from_previous_up_to(before, now, 0),
-                MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
-                MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
-            ]
-        );
-    }
-
-    #[test]
-    fn startup_collected_timeline_metrics_nth_round_at_same_lsn() {
-        let tenant_id = TenantId::generate();
-        let timeline_id = TimelineId::generate();
-
-        let [now, just_before, before, init] = time_backwards();
-
-        let now = DateTime::<Utc>::from(now);
-        let just_before = DateTime::<Utc>::from(just_before);
-        let before = DateTime::<Utc>::from(before);
-
-        let initdb_lsn = Lsn(0x10000);
-        let disk_consistent_lsn = Lsn(initdb_lsn.0 * 2);
-
-        let mut metrics = Vec::new();
-        let cache = HashMap::from([
-            // at t=before was the last time the last_record_lsn changed
-            MetricsKey::written_size(tenant_id, timeline_id).at(before, disk_consistent_lsn.0),
-            // end time of this event is used for the next ones
-            MetricsKey::written_size_delta(tenant_id, timeline_id).from_previous_up_to(
-                before,
-                just_before,
-                0,
-            ),
-        ]);
-
-        let snap = TimelineSnapshot {
-            loaded_at: (disk_consistent_lsn, init),
-            last_record_lsn: disk_consistent_lsn,
-            current_exact_logical_size: Some(0x42000),
-        };
-
-        snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
-
-        assert_eq!(
-            metrics,
-            &[
-                MetricsKey::written_size_delta(tenant_id, timeline_id).from_previous_up_to(
-                    just_before,
-                    now,
-                    0
-                ),
-                MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
-                MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
-            ]
-        );
-    }
-
-    fn time_backwards<const N: usize>() -> [std::time::SystemTime; N] {
-        let mut times = [std::time::SystemTime::UNIX_EPOCH; N];
-        times[0] = std::time::SystemTime::now();
-        for behind in 1..N {
-            times[behind] = times[0] - std::time::Duration::from_secs(behind as u64);
-        }
-
-        times
+
+        crate::tenant::tasks::warn_when_period_overrun(
+            tick_at.elapsed(),
+            synthetic_size_calculation_interval,
+            "consumption_metrics_synthetic_size_worker",
+        );
    }
 }
--- a/pageserver/src/consumption_metrics/disk_cache.rs
+++ b/pageserver/src/consumption_metrics/disk_cache.rs
@@ -0,0 +1,117 @@
+use anyhow::Context;
+use std::path::PathBuf;
+use std::sync::Arc;
+
+use super::RawMetric;
+
+pub(super) async fn read_metrics_from_disk(path: Arc<PathBuf>) -> anyhow::Result<Vec<RawMetric>> {
+    // do not add context to each error, callsite will log with full path
+    let span = tracing::Span::current();
+    tokio::task::spawn_blocking(move || {
+        let _e = span.entered();
+
+        if let Some(parent) = path.parent() {
+            if let Err(e) = scan_and_delete_with_same_prefix(&path) {
+                tracing::info!("failed to cleanup temporary files in {parent:?}: {e:#}");
+            }
+        }
+
+        let mut file = std::fs::File::open(&*path)?;
+        let reader = std::io::BufReader::new(&mut file);
+        anyhow::Ok(serde_json::from_reader::<_, Vec<RawMetric>>(reader)?)
+    })
+    .await
+    .context("read metrics join error")
+    .and_then(|x| x)
+}
+
+fn scan_and_delete_with_same_prefix(path: &std::path::Path) -> std::io::Result<()> {
+    let it = std::fs::read_dir(path.parent().expect("caller checked"))?;
+
+    let prefix = path.file_name().expect("caller checked").to_string_lossy();
+
+    for entry in it {
+        let entry = entry?;
+        if !entry.metadata()?.is_file() {
+            continue;
+        }
+        let file_name = entry.file_name();
+
+        if path.file_name().unwrap() == file_name {
+            // do not remove our actual file
+            continue;
+        }
+
+        let file_name = file_name.to_string_lossy();
+
+        if !file_name.starts_with(&*prefix) {
+            continue;
+        }
+
+        let path = entry.path();
+
+        if let Err(e) = std::fs::remove_file(&path) {
+            tracing::warn!("cleaning up old tempfile {file_name:?} failed: {e:#}");
+        } else {
+            tracing::info!("cleaned up old tempfile {file_name:?}");
+        }
+    }
+
+    Ok(())
+}
+
+pub(super) async fn flush_metrics_to_disk(
+    current_metrics: &Arc<Vec<RawMetric>>,
+    path: &Arc<PathBuf>,
+) -> anyhow::Result<()> {
+    use std::io::Write;
+
+    anyhow::ensure!(path.parent().is_some(), "path must have parent: {path:?}");
+    anyhow::ensure!(
+        path.file_name().is_some(),
+        "path must have filename: {path:?}"
+    );
+
+    let span = tracing::Span::current();
+    tokio::task::spawn_blocking({
+        let current_metrics = current_metrics.clone();
+        let path = path.clone();
+        move || {
+            let _e = span.entered();
+
+            let parent = path.parent().expect("existence checked");
+            let file_name = path.file_name().expect("existence checked");
+            let mut tempfile = tempfile::Builder::new()
+                .prefix(file_name)
+                .suffix(".tmp")
+                .tempfile_in(parent)?;
+
+            tracing::debug!("using tempfile {:?}", tempfile.path());
+
+            // write out all of the raw metrics, to be read out later on restart as cached values
+            {
+                let mut writer = std::io::BufWriter::new(&mut tempfile);
+                serde_json::to_writer(&mut writer, &*current_metrics)
+                    .context("serialize metrics")?;
+                writer
+                    .into_inner()
+                    .map_err(|_| anyhow::anyhow!("flushing metrics failed"))?;
+            }
+
+            tempfile.flush()?;
+            tempfile.as_file().sync_all()?;
+
+            fail::fail_point!("before-persist-last-metrics-collected");
+
+            drop(tempfile.persist(&*path).map_err(|e| e.error)?);
+
+            let f = std::fs::File::open(path.parent().unwrap())?;
+            f.sync_all()?;
+
+            anyhow::Ok(())
+        }
+    })
+    .await
+    .with_context(|| format!("write metrics to {path:?} join error"))
+    .and_then(|x| x.with_context(|| format!("write metrics to {path:?}")))
+}
--- a/pageserver/src/consumption_metrics/metrics.rs
+++ b/pageserver/src/consumption_metrics/metrics.rs
@@ -0,0 +1,455 @@
+use crate::context::RequestContext;
+use anyhow::Context;
+use chrono::{DateTime, Utc};
+use consumption_metrics::EventType;
+use futures::stream::StreamExt;
+use serde_with::serde_as;
+use std::{sync::Arc, time::SystemTime};
+use utils::{
+    id::{TenantId, TimelineId},
+    lsn::Lsn,
+};
+
+use super::{Cache, RawMetric};
+
+/// Name of the metric, used by `MetricsKey` factory methods and `deserialize_cached_events`
+/// instead of static str.
+// Do not rename any of these without first consulting with data team and partner
+// management.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+pub(super) enum Name {
+    /// Timeline last_record_lsn, absolute
+    #[serde(rename = "written_size")]
+    WrittenSize,
+    /// Timeline last_record_lsn, incremental
+    #[serde(rename = "written_data_bytes_delta")]
+    WrittenSizeDelta,
+    /// Timeline logical size
+    #[serde(rename = "timeline_logical_size")]
+    LogicalSize,
+    /// Tenant remote size
+    #[serde(rename = "remote_storage_size")]
+    RemoteSize,
+    /// Tenant resident size
+    #[serde(rename = "resident_size")]
+    ResidentSize,
+    /// Tenant synthetic size
+    #[serde(rename = "synthetic_storage_size")]
+    SyntheticSize,
+}
+
+/// Key that uniquely identifies the object this metric describes.
+///
+/// This is a denormalization done at the MetricsKey const methods; these should not be constructed
+/// elsewhere.
+#[serde_with::serde_as]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+pub(crate) struct MetricsKey {
+    #[serde_as(as = "serde_with::DisplayFromStr")]
+    pub(super) tenant_id: TenantId,
+
+    #[serde_as(as = "Option<serde_with::DisplayFromStr>")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(super) timeline_id: Option<TimelineId>,
+
+    pub(super) metric: Name,
+}
+
+impl MetricsKey {
+    const fn absolute_values(self) -> AbsoluteValueFactory {
+        AbsoluteValueFactory(self)
+    }
+    const fn incremental_values(self) -> IncrementalValueFactory {
+        IncrementalValueFactory(self)
+    }
+}
+
+/// Helper type which each individual metric kind can return to produce only absolute values.
+struct AbsoluteValueFactory(MetricsKey);
+
+impl AbsoluteValueFactory {
+    const fn at(self, time: DateTime<Utc>, val: u64) -> RawMetric {
+        let key = self.0;
+        (key, (EventType::Absolute { time }, val))
+    }
+
+    fn key(&self) -> &MetricsKey {
+        &self.0
+    }
+}
+
+/// Helper type which each individual metric kind can return to produce only incremental values.
+struct IncrementalValueFactory(MetricsKey);
+
+impl IncrementalValueFactory {
+    #[allow(clippy::wrong_self_convention)]
+    const fn from_until(
+        self,
+        prev_end: DateTime<Utc>,
+        up_to: DateTime<Utc>,
+        val: u64,
+    ) -> RawMetric {
+        let key = self.0;
+        // cannot assert prev_end < up_to because these are realtime clock based
+        let when = EventType::Incremental {
+            start_time: prev_end,
+            stop_time: up_to,
+        };
+        (key, (when, val))
+    }
+
+    fn key(&self) -> &MetricsKey {
+        &self.0
+    }
+}
+
+// the static part of a MetricsKey
+impl MetricsKey {
+    /// Absolute value of [`Timeline::get_last_record_lsn`].
+    ///
+    /// [`Timeline::get_last_record_lsn`]: crate::tenant::Timeline::get_last_record_lsn
+    const fn written_size(tenant_id: TenantId, timeline_id: TimelineId) -> AbsoluteValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: Some(timeline_id),
+            metric: Name::WrittenSize,
+        }
+        .absolute_values()
+    }
+
+    /// Values will be the difference of the latest [`MetricsKey::written_size`] to what we
+    /// previously sent, starting from the previously sent incremental time range ending at the
+    /// latest absolute measurement.
+    const fn written_size_delta(
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+    ) -> IncrementalValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: Some(timeline_id),
+            metric: Name::WrittenSizeDelta,
+        }
+        .incremental_values()
+    }
+
+    /// Exact [`Timeline::get_current_logical_size`].
+    ///
+    /// [`Timeline::get_current_logical_size`]: crate::tenant::Timeline::get_current_logical_size
+    const fn timeline_logical_size(
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+    ) -> AbsoluteValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: Some(timeline_id),
+            metric: Name::LogicalSize,
+        }
+        .absolute_values()
+    }
+
+    /// [`Tenant::remote_size`]
+    ///
+    /// [`Tenant::remote_size`]: crate::tenant::Tenant::remote_size
+    const fn remote_storage_size(tenant_id: TenantId) -> AbsoluteValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: None,
+            metric: Name::RemoteSize,
+        }
+        .absolute_values()
+    }
+
+    /// Sum of [`Timeline::resident_physical_size`] for each `Tenant`.
+    ///
+    /// [`Timeline::resident_physical_size`]: crate::tenant::Timeline::resident_physical_size
+    const fn resident_size(tenant_id: TenantId) -> AbsoluteValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: None,
+            metric: Name::ResidentSize,
+        }
+        .absolute_values()
+    }
+
+    /// [`Tenant::cached_synthetic_size`] as refreshed by [`calculate_synthetic_size_worker`].
+    ///
+    /// [`Tenant::cached_synthetic_size`]: crate::tenant::Tenant::cached_synthetic_size
+    /// [`calculate_synthetic_size_worker`]: super::calculate_synthetic_size_worker
+    const fn synthetic_size(tenant_id: TenantId) -> AbsoluteValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: None,
+            metric: Name::SyntheticSize,
+        }
+        .absolute_values()
+    }
+}
+
+pub(super) async fn collect_all_metrics(
+    cached_metrics: &Cache,
+    ctx: &RequestContext,
+) -> Vec<RawMetric> {
+    use pageserver_api::models::TenantState;
+
+    let started_at = std::time::Instant::now();
+
+    let tenants = match crate::tenant::mgr::list_tenants().await {
+        Ok(tenants) => tenants,
+        Err(err) => {
+            tracing::error!("failed to list tenants: {:?}", err);
+            return vec![];
+        }
+    };
+
+    let tenants = futures::stream::iter(tenants).filter_map(|(id, state)| async move {
+        if state != TenantState::Active {
+            None
+        } else {
+            crate::tenant::mgr::get_tenant(id, true)
+                .await
+                .ok()
+                .map(|tenant| (id, tenant))
+        }
+    });
+
+    let res = collect(tenants, cached_metrics, ctx).await;
+
+    tracing::info!(
+        elapsed_ms = started_at.elapsed().as_millis(),
+        total = res.len(),
+        "collected metrics"
+    );
+
+    res
+}
+
+async fn collect<S>(tenants: S, cache: &Cache, ctx: &RequestContext) -> Vec<RawMetric>
+where
+    S: futures::stream::Stream<Item = (TenantId, Arc<crate::tenant::Tenant>)>,
+{
+    let mut current_metrics: Vec<RawMetric> = Vec::new();
+
+    let mut tenants = std::pin::pin!(tenants);
+
+    while let Some((tenant_id, tenant)) = tenants.next().await {
+        let mut tenant_resident_size = 0;
+
+        for timeline in tenant.list_timelines() {
+            let timeline_id = timeline.timeline_id;
+
+            match TimelineSnapshot::collect(&timeline, ctx) {
+                Ok(Some(snap)) => {
+                    snap.to_metrics(
+                        tenant_id,
+                        timeline_id,
+                        Utc::now(),
+                        &mut current_metrics,
+                        cache,
+                    );
+                }
+                Ok(None) => {}
+                Err(e) => {
+                    tracing::error!(
+                        "failed to get metrics values for tenant {tenant_id} timeline {}: {e:#?}",
+                        timeline.timeline_id
+                    );
+                    continue;
+                }
+            }
+
+            tenant_resident_size += timeline.resident_physical_size();
+        }
+
+        let snap = TenantSnapshot::collect(&tenant, tenant_resident_size);
+        snap.to_metrics(tenant_id, Utc::now(), cache, &mut current_metrics);
+    }
+
+    current_metrics
+}
+
+/// In-between abstraction to allow testing metrics without actual Tenants.
+struct TenantSnapshot {
+    resident_size: u64,
+    remote_size: u64,
+    synthetic_size: u64,
+}
+
+impl TenantSnapshot {
+    /// Collect tenant status to have metrics created out of it.
+    ///
+    /// `resident_size` is calculated of the timelines we had access to for other metrics, so we
+    /// cannot just list timelines here.
+    fn collect(t: &Arc<crate::tenant::Tenant>, resident_size: u64) -> Self {
+        TenantSnapshot {
+            resident_size,
+            remote_size: t.remote_size(),
+            // Note that this metric is calculated in a separate bgworker
+            // Here we only use cached value, which may lag behind the real latest one
+            synthetic_size: t.cached_synthetic_size(),
+        }
+    }
+
+    fn to_metrics(
+        &self,
+        tenant_id: TenantId,
+        now: DateTime<Utc>,
+        cached: &Cache,
+        metrics: &mut Vec<RawMetric>,
+    ) {
+        let remote_size = MetricsKey::remote_storage_size(tenant_id).at(now, self.remote_size);
+
+        let resident_size = MetricsKey::resident_size(tenant_id).at(now, self.resident_size);
+
+        let synthetic_size = {
+            let factory = MetricsKey::synthetic_size(tenant_id);
+            let mut synthetic_size = self.synthetic_size;
+
+            if synthetic_size == 0 {
+                if let Some((_, value)) = cached.get(factory.key()) {
+                    // use the latest value from previous session
+                    synthetic_size = *value;
+                }
+            }
+
+            if synthetic_size != 0 {
+                // only send non-zeroes because otherwise these show up as errors in logs
+                Some(factory.at(now, synthetic_size))
+            } else {
+                None
+            }
+        };
+
+        metrics.extend(
+            [Some(remote_size), Some(resident_size), synthetic_size]
+                .into_iter()
+                .flatten(),
+        );
+    }
+}
+
+/// Internal type to make timeline metric production testable.
+///
+/// As this value type contains all of the information needed from a timeline to produce the
+/// metrics, it can easily be created with different values in test.
+struct TimelineSnapshot {
+    loaded_at: (Lsn, SystemTime),
+    last_record_lsn: Lsn,
+    current_exact_logical_size: Option<u64>,
+}
+
+impl TimelineSnapshot {
+    /// Collect the metrics from an actual timeline.
+    ///
+    /// Fails currently only when [`Timeline::get_current_logical_size`] fails.
+    ///
+    /// [`Timeline::get_current_logical_size`]: crate::tenant::Timeline::get_current_logical_size
+    fn collect(
+        t: &Arc<crate::tenant::Timeline>,
+        ctx: &RequestContext,
+    ) -> anyhow::Result<Option<Self>> {
+        if !t.is_active() {
+            // no collection for broken or stopping needed, we will still keep the cached values
+            // though at the caller.
+            Ok(None)
+        } else {
+            let loaded_at = t.loaded_at;
+            let last_record_lsn = t.get_last_record_lsn();
+
+            let current_exact_logical_size = {
+                let span = tracing::info_span!("collect_metrics_iteration", tenant_id = %t.tenant_id, timeline_id = %t.timeline_id);
+                let res = span
+                    .in_scope(|| t.get_current_logical_size(ctx))
+                    .context("get_current_logical_size");
+                match res? {
+                    // Only send timeline logical size when it is fully calculated.
+                    (size, is_exact) if is_exact => Some(size),
+                    (_, _) => None,
+                }
+            };
+
+            Ok(Some(TimelineSnapshot {
+                loaded_at,
+                last_record_lsn,
+                current_exact_logical_size,
+            }))
+        }
+    }
+
+    /// Produce the timeline consumption metrics into the `metrics` argument.
+    fn to_metrics(
+        &self,
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+        now: DateTime<Utc>,
+        metrics: &mut Vec<RawMetric>,
+        cache: &Cache,
+    ) {
+        let timeline_written_size = u64::from(self.last_record_lsn);
+
+        let written_size_delta_key = MetricsKey::written_size_delta(tenant_id, timeline_id);
+
+        let last_stop_time = cache
+            .get(written_size_delta_key.key())
+            .map(|(until, _val)| {
+                until
+                    .incremental_timerange()
+                    .expect("never create EventType::Absolute for written_size_delta")
+                    .end
+            });
+
+        let (key, written_size_now) =
+            MetricsKey::written_size(tenant_id, timeline_id).at(now, timeline_written_size);
+
+        // by default, use the last sent written_size as the basis for
+        // calculating the delta. if we don't yet have one, use the load time value.
+        let prev = cache
+            .get(&key)
+            .map(|(prev_at, prev)| {
+                // use the prev time from our last incremental update, or default to latest
+                // absolute update on the first round.
+                let prev_at = prev_at
+                    .absolute_time()
+                    .expect("never create EventType::Incremental for written_size");
+                let prev_at = last_stop_time.unwrap_or(prev_at);
+                (*prev_at, *prev)
+            })
+            .unwrap_or_else(|| {
+                // if we don't have a previous point of comparison, compare to the load time
+                // lsn.
+                let (disk_consistent_lsn, loaded_at) = &self.loaded_at;
+                (DateTime::from(*loaded_at), disk_consistent_lsn.0)
+            });
+
+        let up_to = now;
+
+        if let Some(delta) = written_size_now.1.checked_sub(prev.1) {
+            let key_value = written_size_delta_key.from_until(prev.0, up_to, delta);
+            // written_size_delta
+            metrics.push(key_value);
+            // written_size
+            metrics.push((key, written_size_now));
+        } else {
+            // the cached value was ahead of us, report zero until we've caught up
+            metrics.push(written_size_delta_key.from_until(prev.0, up_to, 0));
+            // the cached value was ahead of us, report the same until we've caught up
+            metrics.push((key, (written_size_now.0, prev.1)));
+        }
+
+        {
+            let factory = MetricsKey::timeline_logical_size(tenant_id, timeline_id);
+            let current_or_previous = self
+                .current_exact_logical_size
+                .or_else(|| cache.get(factory.key()).map(|(_, val)| *val));
+
+            if let Some(size) = current_or_previous {
+                metrics.push(factory.at(now, size));
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;
+
+#[cfg(test)]
+pub(crate) use tests::metric_examples;
--- a/pageserver/src/consumption_metrics/metrics/tests.rs
+++ b/pageserver/src/consumption_metrics/metrics/tests.rs
@@ -0,0 +1,297 @@
+use super::*;
+use std::collections::HashMap;
+use std::time::SystemTime;
+use utils::lsn::Lsn;
+
+#[test]
+fn startup_collected_timeline_metrics_before_advancing() {
+    let tenant_id = TenantId::generate();
+    let timeline_id = TimelineId::generate();
+
+    let mut metrics = Vec::new();
+    let cache = HashMap::new();
+
+    let initdb_lsn = Lsn(0x10000);
+    let disk_consistent_lsn = Lsn(initdb_lsn.0 * 2);
+
+    let snap = TimelineSnapshot {
+        loaded_at: (disk_consistent_lsn, SystemTime::now()),
+        last_record_lsn: disk_consistent_lsn,
+        current_exact_logical_size: Some(0x42000),
+    };
+
+    let now = DateTime::<Utc>::from(SystemTime::now());
+
+    snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(
+                snap.loaded_at.1.into(),
+                now,
+                0
+            ),
+            MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
+            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
+        ]
+    );
+}
+
+#[test]
+fn startup_collected_timeline_metrics_second_round() {
+    let tenant_id = TenantId::generate();
+    let timeline_id = TimelineId::generate();
+
+    let [now, before, init] = time_backwards();
+
+    let now = DateTime::<Utc>::from(now);
+    let before = DateTime::<Utc>::from(before);
+
+    let initdb_lsn = Lsn(0x10000);
+    let disk_consistent_lsn = Lsn(initdb_lsn.0 * 2);
+
+    let mut metrics = Vec::new();
+    let cache = HashMap::from([
+        MetricsKey::written_size(tenant_id, timeline_id).at(before, disk_consistent_lsn.0)
+    ]);
+
+    let snap = TimelineSnapshot {
+        loaded_at: (disk_consistent_lsn, init),
+        last_record_lsn: disk_consistent_lsn,
+        current_exact_logical_size: Some(0x42000),
+    };
+
+    snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(before, now, 0),
+            MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
+            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
+        ]
+    );
+}
+
+#[test]
+fn startup_collected_timeline_metrics_nth_round_at_same_lsn() {
+    let tenant_id = TenantId::generate();
+    let timeline_id = TimelineId::generate();
+
+    let [now, just_before, before, init] = time_backwards();
+
+    let now = DateTime::<Utc>::from(now);
+    let just_before = DateTime::<Utc>::from(just_before);
+    let before = DateTime::<Utc>::from(before);
+
+    let initdb_lsn = Lsn(0x10000);
+    let disk_consistent_lsn = Lsn(initdb_lsn.0 * 2);
+
+    let mut metrics = Vec::new();
+    let cache = HashMap::from([
+        // at t=before was the last time the last_record_lsn changed
+        MetricsKey::written_size(tenant_id, timeline_id).at(before, disk_consistent_lsn.0),
+        // end time of this event is used for the next ones
+        MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(before, just_before, 0),
+    ]);
+
+    let snap = TimelineSnapshot {
+        loaded_at: (disk_consistent_lsn, init),
+        last_record_lsn: disk_consistent_lsn,
+        current_exact_logical_size: Some(0x42000),
+    };
+
+    snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(just_before, now, 0),
+            MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
+            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
+        ]
+    );
+}
+
+#[test]
+fn post_restart_written_sizes_with_rolled_back_last_record_lsn() {
+    // it can happen that we lose the inmemorylayer but have previously sent metrics and we
+    // should never go backwards
+
+    let tenant_id = TenantId::generate();
+    let timeline_id = TimelineId::generate();
+
+    let [later, now, at_restart] = time_backwards();
+
+    // FIXME: tests would be so much easier if we did not need to juggle back and forth
+    // SystemTime and DateTime::<Utc> ... Could do the conversion only at upload time?
+    let now = DateTime::<Utc>::from(now);
+    let later = DateTime::<Utc>::from(later);
+    let before_restart = at_restart - std::time::Duration::from_secs(5 * 60);
+    let way_before = before_restart - std::time::Duration::from_secs(10 * 60);
+    let before_restart = DateTime::<Utc>::from(before_restart);
+    let way_before = DateTime::<Utc>::from(way_before);
+
+    let snap = TimelineSnapshot {
+        loaded_at: (Lsn(50), at_restart),
+        last_record_lsn: Lsn(50),
+        current_exact_logical_size: None,
+    };
+
+    let mut cache = HashMap::from([
+        MetricsKey::written_size(tenant_id, timeline_id).at(before_restart, 100),
+        MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(
+            way_before,
+            before_restart,
+            // not taken into account, but the timestamps are important
+            999_999_999,
+        ),
+    ]);
+
+    let mut metrics = Vec::new();
+    snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(
+                before_restart,
+                now,
+                0
+            ),
+            MetricsKey::written_size(tenant_id, timeline_id).at(now, 100),
+        ]
+    );
+
+    // now if we cache these metrics, and re-run while "still in recovery"
+    cache.extend(metrics.drain(..));
+
+    // "still in recovery", because our snapshot did not change
+    snap.to_metrics(tenant_id, timeline_id, later, &mut metrics, &cache);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(now, later, 0),
+            MetricsKey::written_size(tenant_id, timeline_id).at(later, 100),
+        ]
+    );
+}
+
+#[test]
+fn post_restart_current_exact_logical_size_uses_cached() {
+    let tenant_id = TenantId::generate();
+    let timeline_id = TimelineId::generate();
+
+    let [now, at_restart] = time_backwards();
+
+    let now = DateTime::<Utc>::from(now);
+    let before_restart = at_restart - std::time::Duration::from_secs(5 * 60);
+    let before_restart = DateTime::<Utc>::from(before_restart);
+
+    let snap = TimelineSnapshot {
+        loaded_at: (Lsn(50), at_restart),
+        last_record_lsn: Lsn(50),
+        current_exact_logical_size: None,
+    };
+
+    let cache = HashMap::from([
+        MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(before_restart, 100)
+    ]);
+
+    let mut metrics = Vec::new();
+    snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
+
+    metrics.retain(|(key, _)| key.metric == Name::LogicalSize);
+
+    assert_eq!(
+        metrics,
+        &[MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 100)]
+    );
+}
+
+#[test]
+fn post_restart_synthetic_size_uses_cached_if_available() {
+    let tenant_id = TenantId::generate();
+
+    let ts = TenantSnapshot {
+        resident_size: 1000,
+        remote_size: 1000,
+        // not yet calculated
+        synthetic_size: 0,
+    };
+
+    let now = SystemTime::now();
+    let before_restart = DateTime::<Utc>::from(now - std::time::Duration::from_secs(5 * 60));
+    let now = DateTime::<Utc>::from(now);
+
+    let cached = HashMap::from([MetricsKey::synthetic_size(tenant_id).at(before_restart, 1000)]);
+
+    let mut metrics = Vec::new();
+    ts.to_metrics(tenant_id, now, &cached, &mut metrics);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::remote_storage_size(tenant_id).at(now, 1000),
+            MetricsKey::resident_size(tenant_id).at(now, 1000),
+            MetricsKey::synthetic_size(tenant_id).at(now, 1000),
+        ]
+    );
+}
+
+#[test]
+fn post_restart_synthetic_size_is_not_sent_when_not_cached() {
+    let tenant_id = TenantId::generate();
+
+    let ts = TenantSnapshot {
+        resident_size: 1000,
+        remote_size: 1000,
+        // not yet calculated
+        synthetic_size: 0,
+    };
+
+    let now = SystemTime::now();
+    let now = DateTime::<Utc>::from(now);
+
+    let cached = HashMap::new();
+
+    let mut metrics = Vec::new();
+    ts.to_metrics(tenant_id, now, &cached, &mut metrics);
+
+    assert_eq!(
+        metrics,
+        &[
+            MetricsKey::remote_storage_size(tenant_id).at(now, 1000),
+            MetricsKey::resident_size(tenant_id).at(now, 1000),
+            // no synthetic size here
+        ]
+    );
+}
+
+fn time_backwards<const N: usize>() -> [std::time::SystemTime; N] {
+    let mut times = [std::time::SystemTime::UNIX_EPOCH; N];
+    times[0] = std::time::SystemTime::now();
+    for behind in 1..N {
+        times[behind] = times[0] - std::time::Duration::from_secs(behind as u64);
+    }
+
+    times
+}
+
+pub(crate) const fn metric_examples(
+    tenant_id: TenantId,
+    timeline_id: TimelineId,
+    now: DateTime<Utc>,
+    before: DateTime<Utc>,
+) -> [RawMetric; 6] {
+    [
+        MetricsKey::written_size(tenant_id, timeline_id).at(now, 0),
+        MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(before, now, 0),
+        MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0),
+        MetricsKey::remote_storage_size(tenant_id).at(now, 0),
+        MetricsKey::resident_size(tenant_id).at(now, 0),
+        MetricsKey::synthetic_size(tenant_id).at(now, 1),
+    ]
+}
--- a/pageserver/src/consumption_metrics/upload.rs
+++ b/pageserver/src/consumption_metrics/upload.rs
@@ -0,0 +1,443 @@
+use consumption_metrics::{Event, EventChunk, IdempotencyKey, CHUNK_SIZE};
+use serde_with::serde_as;
+use tokio_util::sync::CancellationToken;
+use tracing::Instrument;
+
+use super::{metrics::Name, Cache, MetricsKey, RawMetric};
+use utils::id::{TenantId, TimelineId};
+
+/// How the metrics from pageserver are identified.
+#[serde_with::serde_as]
+#[derive(serde::Serialize, serde::Deserialize, Debug, Clone, Copy, PartialEq)]
+struct Ids {
+    #[serde_as(as = "serde_with::DisplayFromStr")]
+    pub(super) tenant_id: TenantId,
+    #[serde_as(as = "Option<serde_with::DisplayFromStr>")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(super) timeline_id: Option<TimelineId>,
+}
+
+#[tracing::instrument(skip_all, fields(metrics_total = %metrics.len()))]
+pub(super) async fn upload_metrics(
+    client: &reqwest::Client,
+    metric_collection_endpoint: &reqwest::Url,
+    cancel: &CancellationToken,
+    node_id: &str,
+    metrics: &[RawMetric],
+    cached_metrics: &mut Cache,
+) -> anyhow::Result<()> {
+    let mut uploaded = 0;
+    let mut failed = 0;
+
+    let started_at = std::time::Instant::now();
+
+    let mut iter = serialize_in_chunks(CHUNK_SIZE, metrics, node_id);
+
+    while let Some(res) = iter.next() {
+        let (chunk, body) = res?;
+
+        let event_bytes = body.len();
+
+        let is_last = iter.len() == 0;
+
+        let res = upload(client, metric_collection_endpoint, body, cancel, is_last)
+            .instrument(tracing::info_span!(
+                "upload",
+                %event_bytes,
+                uploaded,
+                total = metrics.len(),
+            ))
+            .await;
+
+        match res {
+            Ok(()) => {
+                for (curr_key, curr_val) in chunk {
+                    cached_metrics.insert(*curr_key, *curr_val);
+                }
+                uploaded += chunk.len();
+            }
+            Err(_) => {
+                // failure(s) have already been logged
+                //
+                // however this is an inconsistency: if we crash here, we will start with the
+                // values as uploaded. in practice, the rejections no longer happen.
+                failed += chunk.len();
+            }
+        }
+    }
+
+    let elapsed = started_at.elapsed();
+
+    tracing::info!(
+        uploaded,
+        failed,
+        elapsed_ms = elapsed.as_millis(),
+        "done sending metrics"
+    );
+
+    Ok(())
+}
+
+// The return type is quite ugly, but we gain testability in isolation
+fn serialize_in_chunks<'a, F>(
+    chunk_size: usize,
+    input: &'a [RawMetric],
+    factory: F,
+) -> impl ExactSizeIterator<Item = Result<(&'a [RawMetric], bytes::Bytes), serde_json::Error>> + 'a
+where
+    F: KeyGen<'a> + 'a,
+{
+    use bytes::BufMut;
+
+    struct Iter<'a, F> {
+        inner: std::slice::Chunks<'a, RawMetric>,
+        chunk_size: usize,
+
+        // write to a BytesMut so that we can cheaply clone the frozen Bytes for retries
+        buffer: bytes::BytesMut,
+        // chunk amount of events are reused to produce the serialized document
+        scratch: Vec<Event<Ids, Name>>,
+        factory: F,
+    }
+
+    impl<'a, F: KeyGen<'a>> Iterator for Iter<'a, F> {
+        type Item = Result<(&'a [RawMetric], bytes::Bytes), serde_json::Error>;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            let chunk = self.inner.next()?;
+
+            if self.scratch.is_empty() {
+                // first round: create events with N strings
+                self.scratch.extend(
+                    chunk
+                        .iter()
+                        .map(|raw_metric| raw_metric.as_event(&self.factory.generate())),
+                );
+            } else {
+                // next rounds: update_in_place to reuse allocations
+                assert_eq!(self.scratch.len(), self.chunk_size);
+                self.scratch
+                    .iter_mut()
+                    .zip(chunk.iter())
+                    .for_each(|(slot, raw_metric)| {
+                        raw_metric.update_in_place(slot, &self.factory.generate())
+                    });
+            }
+
+            let res = serde_json::to_writer(
+                (&mut self.buffer).writer(),
+                &EventChunk {
+                    events: (&self.scratch[..chunk.len()]).into(),
+                },
+            );
+
+            match res {
+                Ok(()) => Some(Ok((chunk, self.buffer.split().freeze()))),
+                Err(e) => Some(Err(e)),
+            }
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            self.inner.size_hint()
+        }
+    }
+
+    impl<'a, F: KeyGen<'a>> ExactSizeIterator for Iter<'a, F> {}
+
+    let buffer = bytes::BytesMut::new();
+    let inner = input.chunks(chunk_size);
+    let scratch = Vec::new();
+
+    Iter {
+        inner,
+        chunk_size,
+        buffer,
+        scratch,
+        factory,
+    }
+}
+
+trait RawMetricExt {
+    fn as_event(&self, key: &IdempotencyKey<'_>) -> Event<Ids, Name>;
+    fn update_in_place(&self, event: &mut Event<Ids, Name>, key: &IdempotencyKey<'_>);
+}
+
+impl RawMetricExt for RawMetric {
+    fn as_event(&self, key: &IdempotencyKey<'_>) -> Event<Ids, Name> {
+        let MetricsKey {
+            metric,
+            tenant_id,
+            timeline_id,
+        } = self.0;
+
+        let (kind, value) = self.1;
+
+        Event {
+            kind,
+            metric,
+            idempotency_key: key.to_string(),
+            value,
+            extra: Ids {
+                tenant_id,
+                timeline_id,
+            },
+        }
+    }
+
+    fn update_in_place(&self, event: &mut Event<Ids, Name>, key: &IdempotencyKey<'_>) {
+        use std::fmt::Write;
+
+        let MetricsKey {
+            metric,
+            tenant_id,
+            timeline_id,
+        } = self.0;
+
+        let (kind, value) = self.1;
+
+        *event = Event {
+            kind,
+            metric,
+            idempotency_key: {
+                event.idempotency_key.clear();
+                write!(event.idempotency_key, "{key}").unwrap();
+                std::mem::take(&mut event.idempotency_key)
+            },
+            value,
+            extra: Ids {
+                tenant_id,
+                timeline_id,
+            },
+        };
+    }
+}
+
+trait KeyGen<'a>: Copy {
+    fn generate(&self) -> IdempotencyKey<'a>;
+}
+
+impl<'a> KeyGen<'a> for &'a str {
+    fn generate(&self) -> IdempotencyKey<'a> {
+        IdempotencyKey::generate(self)
+    }
+}
+
+enum UploadError {
+    Rejected(reqwest::StatusCode),
+    Reqwest(reqwest::Error),
+    Cancelled,
+}
+
+impl std::fmt::Debug for UploadError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        // use same impl because backoff::retry will log this using both
+        std::fmt::Display::fmt(self, f)
+    }
+}
+
+impl std::fmt::Display for UploadError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use UploadError::*;
+
+        match self {
+            Rejected(code) => write!(f, "server rejected the metrics with {code}"),
+            Reqwest(e) => write!(f, "request failed: {e}"),
+            Cancelled => write!(f, "cancelled"),
+        }
+    }
+}
+
+impl UploadError {
+    fn is_reject(&self) -> bool {
+        matches!(self, UploadError::Rejected(_))
+    }
+}
+
+// this is consumed by the test verifiers
+static LAST_IN_BATCH: reqwest::header::HeaderName =
+    reqwest::header::HeaderName::from_static("pageserver-metrics-last-upload-in-batch");
+
+async fn upload(
+    client: &reqwest::Client,
+    metric_collection_endpoint: &reqwest::Url,
+    body: bytes::Bytes,
+    cancel: &CancellationToken,
+    is_last: bool,
+) -> Result<(), UploadError> {
+    let warn_after = 3;
+    let max_attempts = 10;
+    let res = utils::backoff::retry(
+        move || {
+            let body = body.clone();
+            async move {
+                let res = client
+                    .post(metric_collection_endpoint.clone())
+                    .header(reqwest::header::CONTENT_TYPE, "application/json")
+                    .header(
+                        LAST_IN_BATCH.clone(),
+                        if is_last { "true" } else { "false" },
+                    )
+                    .body(body)
+                    .send()
+                    .await;
+
+                let res = res.and_then(|res| res.error_for_status());
+
+                // 10 redirects are normally allowed, so we don't need worry about 3xx
+                match res {
+                    Ok(_response) => Ok(()),
+                    Err(e) => {
+                        let status = e.status().filter(|s| s.is_client_error());
+                        if let Some(status) = status {
+                            // rejection used to be a thing when the server could reject a
+                            // whole batch of metrics if one metric was bad.
+                            Err(UploadError::Rejected(status))
+                        } else {
+                            Err(UploadError::Reqwest(e))
+                        }
+                    }
+                }
+            }
+        },
+        UploadError::is_reject,
+        warn_after,
+        max_attempts,
+        "upload consumption_metrics",
+        utils::backoff::Cancel::new(cancel.clone(), || UploadError::Cancelled),
+    )
+    .await;
+
+    match &res {
+        Ok(_) => {}
+        Err(e) if e.is_reject() => {
+            // permanent errors currently do not get logged by backoff::retry
+            // display alternate has no effect, but keeping it here for easier pattern matching.
+            tracing::error!("failed to upload metrics: {e:#}");
+        }
+        Err(_) => {
+            // these have been logged already
+        }
+    }
+
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::{DateTime, Utc};
+    use once_cell::sync::Lazy;
+
+    #[test]
+    fn chunked_serialization() {
+        let examples = metric_samples();
+        assert!(examples.len() > 1);
+
+        let factory = FixedGen::new(Utc::now(), "1", 42);
+
+        // need to use Event here because serde_json::Value uses default hashmap, not linked
+        // hashmap
+        #[derive(serde::Deserialize)]
+        struct EventChunk {
+            events: Vec<Event<Ids, Name>>,
+        }
+
+        let correct = serialize_in_chunks(examples.len(), &examples, factory)
+            .map(|res| res.unwrap().1)
+            .flat_map(|body| serde_json::from_slice::<EventChunk>(&body).unwrap().events)
+            .collect::<Vec<_>>();
+
+        for chunk_size in 1..examples.len() {
+            let actual = serialize_in_chunks(chunk_size, &examples, factory)
+                .map(|res| res.unwrap().1)
+                .flat_map(|body| serde_json::from_slice::<EventChunk>(&body).unwrap().events)
+                .collect::<Vec<_>>();
+
+            // if these are equal, it means that multi-chunking version works as well
+            assert_eq!(correct, actual);
+        }
+    }
+
+    #[derive(Clone, Copy)]
+    struct FixedGen<'a>(chrono::DateTime<chrono::Utc>, &'a str, u16);
+
+    impl<'a> FixedGen<'a> {
+        fn new(now: chrono::DateTime<chrono::Utc>, node_id: &'a str, nonce: u16) -> Self {
+            FixedGen(now, node_id, nonce)
+        }
+    }
+
+    impl<'a> KeyGen<'a> for FixedGen<'a> {
+        fn generate(&self) -> IdempotencyKey<'a> {
+            IdempotencyKey::for_tests(self.0, self.1, self.2)
+        }
+    }
+
+    static SAMPLES_NOW: Lazy<DateTime<Utc>> = Lazy::new(|| {
+        DateTime::parse_from_rfc3339("2023-09-15T00:00:00.123456789Z")
+            .unwrap()
+            .into()
+    });
+
+    #[test]
+    fn metric_image_stability() {
+        // it is important that these strings stay as they are
+
+        let examples = [
+            (
+                line!(),
+                r#"{"type":"absolute","time":"2023-09-15T00:00:00.123456789Z","metric":"written_size","idempotency_key":"2023-09-15 00:00:00.123456789 UTC-1-0000","value":0,"tenant_id":"00000000000000000000000000000000","timeline_id":"ffffffffffffffffffffffffffffffff"}"#,
+            ),
+            (
+                line!(),
+                r#"{"type":"incremental","start_time":"2023-09-14T00:00:00.123456789Z","stop_time":"2023-09-15T00:00:00.123456789Z","metric":"written_data_bytes_delta","idempotency_key":"2023-09-15 00:00:00.123456789 UTC-1-0000","value":0,"tenant_id":"00000000000000000000000000000000","timeline_id":"ffffffffffffffffffffffffffffffff"}"#,
+            ),
+            (
+                line!(),
+                r#"{"type":"absolute","time":"2023-09-15T00:00:00.123456789Z","metric":"timeline_logical_size","idempotency_key":"2023-09-15 00:00:00.123456789 UTC-1-0000","value":0,"tenant_id":"00000000000000000000000000000000","timeline_id":"ffffffffffffffffffffffffffffffff"}"#,
+            ),
+            (
+                line!(),
+                r#"{"type":"absolute","time":"2023-09-15T00:00:00.123456789Z","metric":"remote_storage_size","idempotency_key":"2023-09-15 00:00:00.123456789 UTC-1-0000","value":0,"tenant_id":"00000000000000000000000000000000"}"#,
+            ),
+            (
+                line!(),
+                r#"{"type":"absolute","time":"2023-09-15T00:00:00.123456789Z","metric":"resident_size","idempotency_key":"2023-09-15 00:00:00.123456789 UTC-1-0000","value":0,"tenant_id":"00000000000000000000000000000000"}"#,
+            ),
+            (
+                line!(),
+                r#"{"type":"absolute","time":"2023-09-15T00:00:00.123456789Z","metric":"synthetic_storage_size","idempotency_key":"2023-09-15 00:00:00.123456789 UTC-1-0000","value":1,"tenant_id":"00000000000000000000000000000000"}"#,
+            ),
+        ];
+
+        let idempotency_key = consumption_metrics::IdempotencyKey::for_tests(*SAMPLES_NOW, "1", 0);
+        let examples = examples.into_iter().zip(metric_samples());
+
+        for ((line, expected), (key, (kind, value))) in examples {
+            let e = consumption_metrics::Event {
+                kind,
+                metric: key.metric,
+                idempotency_key: idempotency_key.to_string(),
+                value,
+                extra: Ids {
+                    tenant_id: key.tenant_id,
+                    timeline_id: key.timeline_id,
+                },
+            };
+            let actual = serde_json::to_string(&e).unwrap();
+            assert_eq!(expected, actual, "example for {kind:?} from line {line}");
+        }
+    }
+
+    fn metric_samples() -> [RawMetric; 6] {
+        let tenant_id = TenantId::from_array([0; 16]);
+        let timeline_id = TimelineId::from_array([0xff; 16]);
+
+        let before = DateTime::parse_from_rfc3339("2023-09-14T00:00:00.123456789Z")
+            .unwrap()
+            .into();
+        let [now, before] = [*SAMPLES_NOW, before];
+
+        super::super::metrics::metric_examples(tenant_id, timeline_id, now, before)
+    }
+}
--- a/pageserver/src/context.rs
+++ b/pageserver/src/context.rs
@@ -94,6 +94,18 @@ pub struct RequestContext {
    task_kind: TaskKind,
    download_behavior: DownloadBehavior,
    access_stats_behavior: AccessStatsBehavior,
+    page_content_kind: PageContentKind,
+}
+
+/// The kind of access to the page cache.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, enum_map::Enum, strum_macros::IntoStaticStr)]
+pub enum PageContentKind {
+    Unknown,
+    DeltaLayerBtreeNode,
+    DeltaLayerValue,
+    ImageLayerBtreeNode,
+    ImageLayerValue,
+    InMemoryLayer,
 }

 /// Desired behavior if the operation requires an on-demand download
@@ -137,6 +149,7 @@ impl RequestContextBuilder {
                task_kind,
                download_behavior: DownloadBehavior::Download,
                access_stats_behavior: AccessStatsBehavior::Update,
+                page_content_kind: PageContentKind::Unknown,
            },
        }
    }
@@ -149,6 +162,7 @@ impl RequestContextBuilder {
                task_kind: original.task_kind,
                download_behavior: original.download_behavior,
                access_stats_behavior: original.access_stats_behavior,
+                page_content_kind: original.page_content_kind,
            },
        }
    }
@@ -167,6 +181,11 @@ impl RequestContextBuilder {
        self
    }

+    pub(crate) fn page_content_kind(mut self, k: PageContentKind) -> Self {
+        self.inner.page_content_kind = k;
+        self
+    }
+
    pub fn build(self) -> RequestContext {
        self.inner
    }
@@ -263,4 +282,8 @@ impl RequestContext {
    pub(crate) fn access_stats_behavior(&self) -> AccessStatsBehavior {
        self.access_stats_behavior
    }
+
+    pub(crate) fn page_content_kind(&self) -> PageContentKind {
+        self.page_content_kind
+    }
 }
--- a/pageserver/src/control_plane_client.rs
+++ b/pageserver/src/control_plane_client.rs
@@ -0,0 +1,119 @@
+use std::collections::HashMap;
+
+use hyper::StatusCode;
+use pageserver_api::control_api::{ReAttachRequest, ReAttachResponse};
+use tokio_util::sync::CancellationToken;
+use url::Url;
+use utils::{
+    backoff,
+    generation::Generation,
+    id::{NodeId, TenantId},
+};
+
+use crate::config::PageServerConf;
+
+// Backoffs when control plane requests do not succeed: compromise between reducing load
+// on control plane, and retrying frequently when we are blocked on a control plane
+// response to make progress.
+const BACKOFF_INCREMENT: f64 = 0.1;
+const BACKOFF_MAX: f64 = 10.0;
+
+/// The Pageserver's client for using the control plane API: this is a small subset
+/// of the overall control plane API, for dealing with generations (see docs/rfcs/025-generation-numbers.md)
+pub(crate) struct ControlPlaneClient {
+    http_client: reqwest::Client,
+    base_url: Url,
+    node_id: NodeId,
+    cancel: CancellationToken,
+}
+
+impl ControlPlaneClient {
+    /// A None return value indicates that the input `conf` object does not have control
+    /// plane API enabled.
+    pub(crate) fn new(conf: &'static PageServerConf, cancel: &CancellationToken) -> Option<Self> {
+        let mut url = match conf.control_plane_api.as_ref() {
+            Some(u) => u.clone(),
+            None => return None,
+        };
+
+        if let Ok(mut segs) = url.path_segments_mut() {
+            // This ensures that `url` ends with a slash if it doesn't already.
+            // That way, we can subsequently use join() to safely attach extra path elements.
+            segs.pop_if_empty().push("");
+        }
+
+        let client = reqwest::ClientBuilder::new()
+            .build()
+            .expect("Failed to construct http client");
+
+        Some(Self {
+            http_client: client,
+            base_url: url,
+            node_id: conf.id,
+            cancel: cancel.clone(),
+        })
+    }
+
+    async fn try_re_attach(
+        &self,
+        url: Url,
+        request: &ReAttachRequest,
+    ) -> anyhow::Result<ReAttachResponse> {
+        match self.http_client.post(url).json(request).send().await {
+            Err(e) => Err(anyhow::Error::from(e)),
+            Ok(r) => {
+                if r.status() == StatusCode::OK {
+                    r.json::<ReAttachResponse>()
+                        .await
+                        .map_err(anyhow::Error::from)
+                } else {
+                    Err(anyhow::anyhow!("Unexpected status {}", r.status()))
+                }
+            }
+        }
+    }
+
+    /// Block until we get a successful response
+    pub(crate) async fn re_attach(&self) -> anyhow::Result<HashMap<TenantId, Generation>> {
+        let re_attach_path = self
+            .base_url
+            .join("re-attach")
+            .expect("Failed to build re-attach path");
+        let request = ReAttachRequest {
+            node_id: self.node_id,
+        };
+
+        let mut attempt = 0;
+        loop {
+            let result = self.try_re_attach(re_attach_path.clone(), &request).await;
+            match result {
+                Ok(res) => {
+                    tracing::info!(
+                        "Received re-attach response with {} tenants",
+                        res.tenants.len()
+                    );
+
+                    return Ok(res
+                        .tenants
+                        .into_iter()
+                        .map(|t| (t.id, Generation::new(t.generation)))
+                        .collect::<HashMap<_, _>>());
+                }
+                Err(e) => {
+                    tracing::error!("Error re-attaching tenants, retrying: {e:#}");
+                    backoff::exponential_backoff(
+                        attempt,
+                        BACKOFF_INCREMENT,
+                        BACKOFF_MAX,
+                        &self.cancel,
+                    )
+                    .await;
+                    if self.cancel.is_cancelled() {
+                        return Err(anyhow::anyhow!("Shutting down"));
+                    }
+                    attempt += 1;
+                }
+            }
+        }
+    }
+}
--- a/pageserver/src/http/openapi_spec.yml
+++ b/pageserver/src/http/openapi_spec.yml
@@ -383,7 +383,6 @@ paths:
        schema:
          type: string
          format: hex
-
    post:
      description: |
        Schedules attach operation to happen in the background for the given tenant.
@@ -1020,6 +1019,9 @@ components:
      properties:
        config:
          $ref: '#/components/schemas/TenantConfig'
+        generation:
+          type: integer
+          description: Attachment generation number.
    TenantConfigRequest:
      allOf:
        - $ref: '#/components/schemas/TenantConfig'
--- a/pageserver/src/http/routes.rs
+++ b/pageserver/src/http/routes.rs
@@ -8,9 +8,10 @@ use anyhow::{anyhow, Context, Result};
 use hyper::StatusCode;
 use hyper::{Body, Request, Response, Uri};
 use metrics::launch_timestamp::LaunchTimestamp;
-use pageserver_api::models::{DownloadRemoteLayersTaskSpawnRequest, TenantAttachRequest};
+use pageserver_api::models::{
+    DownloadRemoteLayersTaskSpawnRequest, TenantAttachRequest, TenantLoadRequest,
+};
 use remote_storage::GenericRemoteStorage;
-use storage_broker::BrokerClientChannel;
 use tenant_size_model::{SizeResult, StorageModel};
 use tokio_util::sync::CancellationToken;
 use tracing::*;
@@ -32,11 +33,13 @@ use crate::tenant::mgr::{
 };
 use crate::tenant::size::ModelInputs;
 use crate::tenant::storage_layer::LayerAccessStatsReset;
-use crate::tenant::{LogicalSizeCalculationCause, PageReconstructError, Timeline};
+use crate::tenant::timeline::Timeline;
+use crate::tenant::{LogicalSizeCalculationCause, PageReconstructError};
 use crate::{config::PageServerConf, tenant::mgr};
 use crate::{disk_usage_eviction_task, tenant};
 use utils::{
    auth::JwtAuth,
+    generation::Generation,
    http::{
        endpoint::{self, attach_openapi_ui, auth_middleware, check_permission_with},
        error::{ApiError, HttpErrorBody},
@@ -51,7 +54,7 @@ use utils::{
 // Imports only used for testing APIs
 use super::models::ConfigureFailpointsRequest;

-struct State {
+pub struct State {
    conf: &'static PageServerConf,
    auth: Option<Arc<JwtAuth>>,
    allowlist_routes: Vec<Uri>,
@@ -61,7 +64,7 @@ struct State {
 }

 impl State {
-    fn new(
+    pub fn new(
        conf: &'static PageServerConf,
        auth: Option<Arc<JwtAuth>>,
        remote_storage: Option<GenericRemoteStorage>,
@@ -282,6 +285,8 @@ async fn build_timeline_info_common(
    let state = timeline.current_state();
    let remote_consistent_lsn = timeline.get_remote_consistent_lsn().unwrap_or(Lsn(0));

+    let walreceiver_status = timeline.walreceiver_status();
+
    let info = TimelineInfo {
        tenant_id: timeline.tenant_id,
        timeline_id: timeline.timeline_id,
@@ -302,6 +307,8 @@ async fn build_timeline_info_common(
        pg_version: timeline.pg_version,

        state,
+
+        walreceiver_status,
    };
    Ok(info)
 }
@@ -472,7 +479,7 @@ async fn tenant_attach_handler(
    check_permission(&request, Some(tenant_id))?;

    let maybe_body: Option<TenantAttachRequest> = json_request_or_empty_body(&mut request).await?;
-    let tenant_conf = match maybe_body {
+    let tenant_conf = match &maybe_body {
        Some(request) => TenantConfOpt::try_from(&*request.config).map_err(ApiError::BadRequest)?,
        None => TenantConfOpt::default(),
    };
@@ -483,10 +490,13 @@ async fn tenant_attach_handler(

    let state = get_state(&request);

+    let generation = get_request_generation(state, maybe_body.as_ref().and_then(|r| r.generation))?;
+
    if let Some(remote_storage) = &state.remote_storage {
        mgr::attach_tenant(
            state.conf,
            tenant_id,
+            generation,
            tenant_conf,
            state.broker_client.clone(),
            remote_storage.clone(),
@@ -538,7 +548,7 @@ async fn tenant_detach_handler(
 }

 async fn tenant_load_handler(
-    request: Request<Body>,
+    mut request: Request<Body>,
    _cancel: CancellationToken,
 ) -> Result<Response<Body>, ApiError> {
    let tenant_id: TenantId = parse_request_param(&request, "tenant_id")?;
@@ -546,10 +556,18 @@ async fn tenant_load_handler(

    let ctx = RequestContext::new(TaskKind::MgmtRequest, DownloadBehavior::Warn);

+    let maybe_body: Option<TenantLoadRequest> = json_request_or_empty_body(&mut request).await?;
+
    let state = get_state(&request);
+
+    // The /load request is only usable when control_plane_api is not set.  Once it is set, callers
+    // should always use /attach instead.
+    let generation = get_request_generation(state, maybe_body.as_ref().and_then(|r| r.generation))?;
+
    mgr::load_tenant(
        state.conf,
        tenant_id,
+        generation,
        state.broker_client.clone(),
        state.remote_storage.clone(),
        &ctx,
@@ -851,6 +869,21 @@ pub fn html_response(status: StatusCode, data: String) -> Result<Response<Body>,
    Ok(response)
 }

+/// Helper for requests that may take a generation, which is mandatory
+/// when control_plane_api is set, but otherwise defaults to Generation::none()
+fn get_request_generation(state: &State, req_gen: Option<u32>) -> Result<Generation, ApiError> {
+    if state.conf.control_plane_api.is_some() {
+        req_gen
+            .map(Generation::new)
+            .ok_or(ApiError::BadRequest(anyhow!(
+                "generation attribute missing"
+            )))
+    } else {
+        // Legacy mode: all tenants operate with no generation
+        Ok(Generation::none())
+    }
+}
+
 async fn tenant_create_handler(
    mut request: Request<Body>,
    _cancel: CancellationToken,
@@ -867,14 +900,17 @@ async fn tenant_create_handler(
    let tenant_conf =
        TenantConfOpt::try_from(&request_data.config).map_err(ApiError::BadRequest)?;

-    let ctx = RequestContext::new(TaskKind::MgmtRequest, DownloadBehavior::Warn);
-
    let state = get_state(&request);

+    let generation = get_request_generation(state, request_data.generation)?;
+
+    let ctx = RequestContext::new(TaskKind::MgmtRequest, DownloadBehavior::Warn);
+
    let new_tenant = mgr::create_tenant(
        state.conf,
        tenant_conf,
        target_tenant_id,
+        generation,
        state.broker_client.clone(),
        state.remote_storage.clone(),
        &ctx,
@@ -1321,12 +1357,9 @@ where
 }

 pub fn make_router(
-    conf: &'static PageServerConf,
+    state: Arc<State>,
    launch_ts: &'static LaunchTimestamp,
    auth: Option<Arc<JwtAuth>>,
-    broker_client: BrokerClientChannel,
-    remote_storage: Option<GenericRemoteStorage>,
-    disk_usage_eviction_state: Arc<disk_usage_eviction_task::State>,
 ) -> anyhow::Result<RouterBuilder<hyper::Body, ApiError>> {
    let spec = include_bytes!("openapi_spec.yml");
    let mut router = attach_openapi_ui(endpoint::make_router(), spec, "/swagger.yml", "/v1/doc");
@@ -1350,16 +1383,7 @@ pub fn make_router(
    );

    Ok(router
-        .data(Arc::new(
-            State::new(
-                conf,
-                auth,
-                remote_storage,
-                broker_client,
-                disk_usage_eviction_state,
-            )
-            .context("Failed to initialize router state")?,
-        ))
+        .data(state)
        .get("/v1/status", |r| api_handler(r, status_handler))
        .put("/v1/failpoints", |r| {
            testing_api_handler("manage failpoints", r, failpoints_handler)
--- a/pageserver/src/import_datadir.rs
+++ b/pageserver/src/import_datadir.rs
@@ -75,12 +75,12 @@ pub async fn import_timeline_from_postgres_datadir(
            {
                pg_control = Some(control_file);
            }
-            modification.flush().await?;
+            modification.flush(ctx).await?;
        }
    }

    // We're done importing all the data files.
-    modification.commit().await?;
+    modification.commit(ctx).await?;

    // We expect the Postgres server to be shut down cleanly.
    let pg_control = pg_control.context("pg_control file not found")?;
@@ -359,7 +359,7 @@ pub async fn import_basebackup_from_tar(
                    // We found the pg_control file.
                    pg_control = Some(res);
                }
-                modification.flush().await?;
+                modification.flush(ctx).await?;
            }
            tokio_tar::EntryType::Directory => {
                debug!("directory {:?}", file_path);
@@ -377,7 +377,7 @@ pub async fn import_basebackup_from_tar(
    // sanity check: ensure that pg_control is loaded
    let _pg_control = pg_control.context("pg_control file not found")?;

-    modification.commit().await?;
+    modification.commit(ctx).await?;
    Ok(())
 }

--- a/pageserver/src/lib.rs
+++ b/pageserver/src/lib.rs
@@ -3,6 +3,7 @@ pub mod basebackup;
 pub mod config;
 pub mod consumption_metrics;
 pub mod context;
+mod control_plane_client;
 pub mod disk_usage_eviction_task;
 pub mod http;
 pub mod import_datadir;
--- a/pageserver/src/metrics.rs
+++ b/pageserver/src/metrics.rs
@@ -1,3 +1,4 @@
+use enum_map::EnumMap;
 use metrics::metric_vec_duration::DurationResultObserver;
 use metrics::{
    register_counter_vec, register_gauge_vec, register_histogram, register_histogram_vec,
@@ -127,22 +128,24 @@ pub(crate) static MATERIALIZED_PAGE_CACHE_HIT: Lazy<IntCounter> = Lazy::new(|| {
    .expect("failed to define a metric")
 });

-pub struct PageCacheMetrics {
+pub struct PageCacheMetricsForTaskKind {
    pub read_accesses_materialized_page: IntCounter,
-    pub read_accesses_ephemeral: IntCounter,
    pub read_accesses_immutable: IntCounter,

-    pub read_hits_ephemeral: IntCounter,
    pub read_hits_immutable: IntCounter,
    pub read_hits_materialized_page_exact: IntCounter,
    pub read_hits_materialized_page_older_lsn: IntCounter,
 }

+pub struct PageCacheMetrics {
+    map: EnumMap<TaskKind, EnumMap<PageContentKind, PageCacheMetricsForTaskKind>>,
+}
+
 static PAGE_CACHE_READ_HITS: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_page_cache_read_hits_total",
        "Number of read accesses to the page cache that hit",
-        &["key_kind", "hit_kind"]
+        &["task_kind", "key_kind", "content_kind", "hit_kind"]
    )
    .expect("failed to define a metric")
 });
@@ -151,55 +154,73 @@ static PAGE_CACHE_READ_ACCESSES: Lazy<IntCounterVec> = Lazy::new(|| {
    register_int_counter_vec!(
        "pageserver_page_cache_read_accesses_total",
        "Number of read accesses to the page cache",
-        &["key_kind"]
+        &["task_kind", "key_kind", "content_kind"]
    )
    .expect("failed to define a metric")
 });

 pub static PAGE_CACHE: Lazy<PageCacheMetrics> = Lazy::new(|| PageCacheMetrics {
-    read_accesses_materialized_page: {
-        PAGE_CACHE_READ_ACCESSES
-            .get_metric_with_label_values(&["materialized_page"])
-            .unwrap()
-    },
+    map: EnumMap::from_array(std::array::from_fn(|task_kind| {
+        let task_kind = <TaskKind as enum_map::Enum>::from_usize(task_kind);
+        let task_kind: &'static str = task_kind.into();
+        EnumMap::from_array(std::array::from_fn(|content_kind| {
+            let content_kind = <PageContentKind as enum_map::Enum>::from_usize(content_kind);
+            let content_kind: &'static str = content_kind.into();
+            PageCacheMetricsForTaskKind {
+                read_accesses_materialized_page: {
+                    PAGE_CACHE_READ_ACCESSES
+                        .get_metric_with_label_values(&[
+                            task_kind,
+                            "materialized_page",
+                            content_kind,
+                        ])
+                        .unwrap()
+                },

-    read_accesses_ephemeral: {
-        PAGE_CACHE_READ_ACCESSES
-            .get_metric_with_label_values(&["ephemeral"])
-            .unwrap()
-    },
+                read_accesses_immutable: {
+                    PAGE_CACHE_READ_ACCESSES
+                        .get_metric_with_label_values(&[task_kind, "immutable", content_kind])
+                        .unwrap()
+                },

-    read_accesses_immutable: {
-        PAGE_CACHE_READ_ACCESSES
-            .get_metric_with_label_values(&["immutable"])
-            .unwrap()
-    },
+                read_hits_immutable: {
+                    PAGE_CACHE_READ_HITS
+                        .get_metric_with_label_values(&[task_kind, "immutable", content_kind, "-"])
+                        .unwrap()
+                },

-    read_hits_ephemeral: {
-        PAGE_CACHE_READ_HITS
-            .get_metric_with_label_values(&["ephemeral", "-"])
-            .unwrap()
-    },
+                read_hits_materialized_page_exact: {
+                    PAGE_CACHE_READ_HITS
+                        .get_metric_with_label_values(&[
+                            task_kind,
+                            "materialized_page",
+                            content_kind,
+                            "exact",
+                        ])
+                        .unwrap()
+                },

-    read_hits_immutable: {
-        PAGE_CACHE_READ_HITS
-            .get_metric_with_label_values(&["immutable", "-"])
-            .unwrap()
-    },
-
-    read_hits_materialized_page_exact: {
-        PAGE_CACHE_READ_HITS
-            .get_metric_with_label_values(&["materialized_page", "exact"])
-            .unwrap()
-    },
-
-    read_hits_materialized_page_older_lsn: {
-        PAGE_CACHE_READ_HITS
-            .get_metric_with_label_values(&["materialized_page", "older_lsn"])
-            .unwrap()
-    },
+                read_hits_materialized_page_older_lsn: {
+                    PAGE_CACHE_READ_HITS
+                        .get_metric_with_label_values(&[
+                            task_kind,
+                            "materialized_page",
+                            content_kind,
+                            "older_lsn",
+                        ])
+                        .unwrap()
+                },
+            }
+        }))
+    })),
 });

+impl PageCacheMetrics {
+    pub(crate) fn for_ctx(&self, ctx: &RequestContext) -> &PageCacheMetricsForTaskKind {
+        &self.map[ctx.task_kind()][ctx.page_content_kind()]
+    }
+}
+
 pub struct PageCacheSizeMetrics {
    pub max_bytes: UIntGauge,

@@ -537,7 +558,7 @@ const STORAGE_IO_TIME_BUCKETS: &[f64] = &[
    30.000,   // 30000 ms
 ];

-/// Tracks time taken by fs operations near VirtualFile.
+/// VirtualFile fs operation variants.
 ///
 /// Operations:
 /// - open ([`std::fs::OpenOptions::open`])
@@ -548,15 +569,66 @@ const STORAGE_IO_TIME_BUCKETS: &[f64] = &[
 /// - seek (modify internal position or file length query)
 /// - fsync ([`std::fs::File::sync_all`])
 /// - metadata ([`std::fs::File::metadata`])
-pub(crate) static STORAGE_IO_TIME: Lazy<HistogramVec> = Lazy::new(|| {
-    register_histogram_vec!(
-        "pageserver_io_operations_seconds",
-        "Time spent in IO operations",
-        &["operation"],
-        STORAGE_IO_TIME_BUCKETS.into()
-    )
-    .expect("failed to define a metric")
-});
+#[derive(
+    Debug, Clone, Copy, strum_macros::EnumCount, strum_macros::EnumIter, strum_macros::FromRepr,
+)]
+pub(crate) enum StorageIoOperation {
+    Open,
+    Close,
+    CloseByReplace,
+    Read,
+    Write,
+    Seek,
+    Fsync,
+    Metadata,
+}
+
+impl StorageIoOperation {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            StorageIoOperation::Open => "open",
+            StorageIoOperation::Close => "close",
+            StorageIoOperation::CloseByReplace => "close-by-replace",
+            StorageIoOperation::Read => "read",
+            StorageIoOperation::Write => "write",
+            StorageIoOperation::Seek => "seek",
+            StorageIoOperation::Fsync => "fsync",
+            StorageIoOperation::Metadata => "metadata",
+        }
+    }
+}
+
+/// Tracks time taken by fs operations near VirtualFile.
+#[derive(Debug)]
+pub(crate) struct StorageIoTime {
+    metrics: [Histogram; StorageIoOperation::COUNT],
+}
+
+impl StorageIoTime {
+    fn new() -> Self {
+        let storage_io_histogram_vec = register_histogram_vec!(
+            "pageserver_io_operations_seconds",
+            "Time spent in IO operations",
+            &["operation"],
+            STORAGE_IO_TIME_BUCKETS.into()
+        )
+        .expect("failed to define a metric");
+        let metrics = std::array::from_fn(|i| {
+            let op = StorageIoOperation::from_repr(i).unwrap();
+            let metric = storage_io_histogram_vec
+                .get_metric_with_label_values(&[op.as_str()])
+                .unwrap();
+            metric
+        });
+        Self { metrics }
+    }
+
+    pub(crate) fn get(&self, op: StorageIoOperation) -> &Histogram {
+        &self.metrics[op as usize]
+    }
+}
+
+pub(crate) static STORAGE_IO_TIME_METRIC: Lazy<StorageIoTime> = Lazy::new(StorageIoTime::new);

 const STORAGE_IO_SIZE_OPERATIONS: &[&str] = &["read", "write"];

@@ -1165,6 +1237,12 @@ impl TimelineMetrics {
            ),
        }
    }
+
+    pub fn record_new_file_metrics(&self, sz: u64) {
+        self.resident_physical_size_gauge.add(sz);
+        self.num_persistent_files_created.inc_by(1);
+        self.persistent_bytes_written.inc_by(sz);
+    }
 }

 impl Drop for TimelineMetrics {
@@ -1223,6 +1301,9 @@ use std::sync::{Arc, Mutex};
 use std::task::{Context, Poll};
 use std::time::{Duration, Instant};

+use crate::context::{PageContentKind, RequestContext};
+use crate::task_mgr::TaskKind;
+
 pub struct RemoteTimelineClientMetrics {
    tenant_id: String,
    timeline_id: String,
--- a/pageserver/src/page_cache.rs
+++ b/pageserver/src/page_cache.rs
@@ -85,7 +85,7 @@ use utils::{
    lsn::Lsn,
 };

-use crate::{metrics::PageCacheSizeMetrics, repository::Key};
+use crate::{context::RequestContext, metrics::PageCacheSizeMetrics, repository::Key};

 static PAGE_CACHE: OnceCell<PageCache> = OnceCell::new();
 const TEST_PAGE_CACHE_SIZE: usize = 50;
@@ -346,8 +346,10 @@ impl PageCache {
        timeline_id: TimelineId,
        key: &Key,
        lsn: Lsn,
+        ctx: &RequestContext,
    ) -> Option<(Lsn, PageReadGuard)> {
        crate::metrics::PAGE_CACHE
+            .for_ctx(ctx)
            .read_accesses_materialized_page
            .inc();

@@ -368,10 +370,12 @@ impl PageCache {
            {
                if available_lsn == lsn {
                    crate::metrics::PAGE_CACHE
+                        .for_ctx(ctx)
                        .read_hits_materialized_page_exact
                        .inc();
                } else {
                    crate::metrics::PAGE_CACHE
+                        .for_ctx(ctx)
                        .read_hits_materialized_page_older_lsn
                        .inc();
                }
@@ -426,10 +430,11 @@ impl PageCache {
        &self,
        file_id: FileId,
        blkno: u32,
+        ctx: &RequestContext,
    ) -> anyhow::Result<ReadBufResult> {
        let mut cache_key = CacheKey::ImmutableFilePage { file_id, blkno };

-        self.lock_for_read(&mut cache_key).await
+        self.lock_for_read(&mut cache_key, ctx).await
    }

    //
@@ -497,14 +502,20 @@ impl PageCache {
    /// }
    /// ```
    ///
-    async fn lock_for_read(&self, cache_key: &mut CacheKey) -> anyhow::Result<ReadBufResult> {
+    async fn lock_for_read(
+        &self,
+        cache_key: &mut CacheKey,
+        ctx: &RequestContext,
+    ) -> anyhow::Result<ReadBufResult> {
        let (read_access, hit) = match cache_key {
            CacheKey::MaterializedPage { .. } => {
                unreachable!("Materialized pages use lookup_materialized_page")
            }
            CacheKey::ImmutableFilePage { .. } => (
-                &crate::metrics::PAGE_CACHE.read_accesses_immutable,
-                &crate::metrics::PAGE_CACHE.read_hits_immutable,
+                &crate::metrics::PAGE_CACHE
+                    .for_ctx(ctx)
+                    .read_accesses_immutable,
+                &crate::metrics::PAGE_CACHE.for_ctx(ctx).read_hits_immutable,
            ),
        };
        read_access.inc();
@@ -799,8 +810,9 @@ impl PageCache {
    fn new(num_pages: usize) -> Self {
        assert!(num_pages > 0, "page cache size must be > 0");

-        // We use Box::leak here and into_boxed_slice to avoid leaking uninitialized
-        // memory that Vec's might contain.
+        // We could use Vec::leak here, but that potentially also leaks
+        // uninitialized reserved capacity. With into_boxed_slice and Box::leak
+        // this is avoided.
        let page_buffer = Box::leak(vec![0u8; num_pages * PAGE_SZ].into_boxed_slice());

        let size_metrics = &crate::metrics::PAGE_CACHE_SIZE;
--- a/pageserver/src/page_service.rs
+++ b/pageserver/src/page_service.rs
@@ -469,7 +469,9 @@ impl PageServerHandler {
        // Create empty timeline
        info!("creating new timeline");
        let tenant = get_active_tenant_with_timeout(tenant_id, &ctx).await?;
-        let timeline = tenant.create_empty_timeline(timeline_id, base_lsn, pg_version, &ctx)?;
+        let timeline = tenant
+            .create_empty_timeline(timeline_id, base_lsn, pg_version, &ctx)
+            .await?;

        // TODO mark timeline as not ready until it reaches end_lsn.
        // We might have some wal to import as well, and we should prevent compute
--- a/pageserver/src/pgdatadir_mapping.rs
+++ b/pageserver/src/pgdatadir_mapping.rs
@@ -1138,7 +1138,7 @@ impl<'a> DatadirModification<'a> {
    /// retains all the metadata, but data pages are flushed. That's again OK
    /// for bulk import, where you are just loading data pages and won't try to
    /// modify the same pages twice.
-    pub async fn flush(&mut self) -> anyhow::Result<()> {
+    pub async fn flush(&mut self, ctx: &RequestContext) -> anyhow::Result<()> {
        // Unless we have accumulated a decent amount of changes, it's not worth it
        // to scan through the pending_updates list.
        let pending_nblocks = self.pending_nblocks;
@@ -1154,7 +1154,7 @@ impl<'a> DatadirModification<'a> {
            if is_rel_block_key(key) || is_slru_block_key(key) {
                // This bails out on first error without modifying pending_updates.
                // That's Ok, cf this function's doc comment.
-                writer.put(key, self.lsn, &value).await?;
+                writer.put(key, self.lsn, &value, ctx).await?;
            } else {
                retained_pending_updates.insert(key, value);
            }
@@ -1174,14 +1174,14 @@ impl<'a> DatadirModification<'a> {
    /// underlying timeline.
    /// All the modifications in this atomic update are stamped by the specified LSN.
    ///
-    pub async fn commit(&mut self) -> anyhow::Result<()> {
+    pub async fn commit(&mut self, ctx: &RequestContext) -> anyhow::Result<()> {
        let writer = self.tline.writer().await;
        let lsn = self.lsn;
        let pending_nblocks = self.pending_nblocks;
        self.pending_nblocks = 0;

        for (key, value) in self.pending_updates.drain() {
-            writer.put(key, lsn, &value).await?;
+            writer.put(key, lsn, &value, ctx).await?;
        }
        for key_range in self.pending_deletions.drain(..) {
            writer.delete(key_range, lsn).await?;
--- a/pageserver/src/task_mgr.rs
+++ b/pageserver/src/task_mgr.rs
@@ -187,6 +187,7 @@ task_local! {
    Debug,
    // NB: enumset::EnumSetType derives PartialEq, Eq, Clone, Copy
    enumset::EnumSetType,
+    enum_map::Enum,
    serde::Serialize,
    serde::Deserialize,
    strum_macros::IntoStaticStr,
--- a/pageserver/src/tenant.rs
+++ b/pageserver/src/tenant.rs
@@ -32,9 +32,7 @@ use std::fmt::Debug;
 use std::fmt::Display;
 use std::fs;
 use std::fs::File;
-use std::fs::OpenOptions;
 use std::io;
-use std::io::Write;
 use std::ops::Bound::Included;
 use std::path::Path;
 use std::path::PathBuf;
@@ -68,7 +66,7 @@ use crate::task_mgr;
 use crate::task_mgr::TaskKind;
 use crate::tenant::config::TenantConfOpt;
 use crate::tenant::metadata::load_metadata;
-use crate::tenant::remote_timeline_client::index::IndexPart;
+pub use crate::tenant::remote_timeline_client::index::IndexPart;
 use crate::tenant::remote_timeline_client::MaybeDeletedIndexPart;
 use crate::tenant::storage_layer::DeltaLayer;
 use crate::tenant::storage_layer::ImageLayer;
@@ -85,6 +83,7 @@ pub use pageserver_api::models::TenantState;
 use toml_edit;
 use utils::{
    crashsafe,
+    generation::Generation,
    id::{TenantId, TimelineId},
    lsn::{Lsn, RecordLsn},
 };
@@ -114,7 +113,6 @@ pub mod block_io;
 pub mod disk_btree;
 pub(crate) mod ephemeral_file;
 pub mod layer_map;
-pub mod manifest;
 mod span;

 pub mod metadata;
@@ -143,6 +141,9 @@ pub use crate::tenant::metadata::save_metadata;
 // re-export for use in walreceiver
 pub use crate::tenant::timeline::WalReceiverInfo;

+/// The "tenants" part of `tenants/<tenant>/timelines...`
+pub const TENANTS_SEGMENT_NAME: &str = "tenants";
+
 /// Parts of the `.neon/tenants/<tenant_id>/timelines/<timeline_id>` directory prefix.
 pub const TIMELINES_SEGMENT_NAME: &str = "timelines";

@@ -178,6 +179,11 @@ pub struct Tenant {
    tenant_conf: Arc<RwLock<TenantConfOpt>>,

    tenant_id: TenantId,
+
+    /// The remote storage generation, used to protect S3 objects from split-brain.
+    /// Does not change over the lifetime of the [`Tenant`] object.
+    generation: Generation,
+
    timelines: Mutex<HashMap<TimelineId, Arc<Timeline>>>,
    // This mutex prevents creation of new timelines during GC.
    // Adding yet another mutex (in addition to `timelines`) is needed because holding
@@ -189,7 +195,7 @@ pub struct Tenant {
    walredo_mgr: Arc<dyn WalRedoManager + Send + Sync>,

    // provides access to timeline data sitting in the remote storage
-    remote_storage: Option<GenericRemoteStorage>,
+    pub(crate) remote_storage: Option<GenericRemoteStorage>,

    /// Cached logical sizes updated updated on each [`Tenant::gather_size_inputs`].
    cached_logical_sizes: tokio::sync::Mutex<HashMap<(TimelineId, Lsn), u64>>,
@@ -401,7 +407,6 @@ impl Tenant {
        remote_startup_data: Option<RemoteStartupData>,
        local_metadata: Option<TimelineMetadata>,
        ancestor: Option<Arc<Timeline>>,
-        first_save: bool,
        init_order: Option<&InitializationOrder>,
        _ctx: &RequestContext,
    ) -> anyhow::Result<()> {
@@ -435,14 +440,9 @@ impl Tenant {

        // Save the metadata file to local disk.
        if !picked_local {
-            save_metadata(
-                self.conf,
-                &tenant_id,
-                &timeline_id,
-                up_to_date_metadata,
-                first_save,
-            )
-            .context("save_metadata")?;
+            save_metadata(self.conf, &tenant_id, &timeline_id, up_to_date_metadata)
+                .await
+                .context("save_metadata")?;
        }

        let index_part = remote_startup_data.as_ref().map(|x| &x.index_part);
@@ -522,6 +522,7 @@ impl Tenant {
    pub(crate) fn spawn_attach(
        conf: &'static PageServerConf,
        tenant_id: TenantId,
+        generation: Generation,
        broker_client: storage_broker::BrokerClientChannel,
        tenants: &'static tokio::sync::RwLock<TenantsMap>,
        remote_storage: GenericRemoteStorage,
@@ -538,6 +539,7 @@ impl Tenant {
            tenant_conf,
            wal_redo_manager,
            tenant_id,
+            generation,
            Some(remote_storage.clone()),
        ));

@@ -648,12 +650,8 @@ impl Tenant {
            .as_ref()
            .ok_or_else(|| anyhow::anyhow!("cannot attach without remote storage"))?;

-        let remote_timeline_ids = remote_timeline_client::list_remote_timelines(
-            remote_storage,
-            self.conf,
-            self.tenant_id,
-        )
-        .await?;
+        let remote_timeline_ids =
+            remote_timeline_client::list_remote_timelines(remote_storage, self.tenant_id).await?;

        info!("found {} timelines", remote_timeline_ids.len());

@@ -665,6 +663,7 @@ impl Tenant {
                self.conf,
                self.tenant_id,
                timeline_id,
+                self.generation,
            );
            part_downloads.spawn(
                async move {
@@ -828,7 +827,6 @@ impl Tenant {
            }),
            local_metadata,
            ancestor,
-            true,
            None,
            ctx,
        )
@@ -851,6 +849,7 @@ impl Tenant {
            TenantConfOpt::default(),
            wal_redo_manager,
            tenant_id,
+            Generation::broken(),
            None,
        ))
    }
@@ -868,6 +867,7 @@ impl Tenant {
    pub(crate) fn spawn_load(
        conf: &'static PageServerConf,
        tenant_id: TenantId,
+        generation: Generation,
        resources: TenantSharedResources,
        init_order: Option<InitializationOrder>,
        tenants: &'static tokio::sync::RwLock<TenantsMap>,
@@ -893,6 +893,7 @@ impl Tenant {
            tenant_conf,
            wal_redo_manager,
            tenant_id,
+            generation,
            remote_storage.clone(),
        );
        let tenant = Arc::new(tenant);
@@ -1378,7 +1379,6 @@ impl Tenant {
            remote_startup_data,
            Some(local_metadata),
            ancestor,
-            false,
            init_order,
            ctx,
        )
@@ -1442,7 +1442,7 @@ impl Tenant {
    /// For tests, use `DatadirModification::init_empty_test_timeline` + `commit` to setup the
    /// minimum amount of keys required to get a writable timeline.
    /// (Without it, `put` might fail due to `repartition` failing.)
-    pub fn create_empty_timeline(
+    pub async fn create_empty_timeline(
        &self,
        new_timeline_id: TimelineId,
        initdb_lsn: Lsn,
@@ -1454,10 +1454,10 @@ impl Tenant {
            "Cannot create empty timelines on inactive tenant"
        );

-        let timelines = self.timelines.lock().unwrap();
-        let timeline_uninit_mark = self.create_timeline_uninit_mark(new_timeline_id, &timelines)?;
-        drop(timelines);
-
+        let timeline_uninit_mark = {
+            let timelines = self.timelines.lock().unwrap();
+            self.create_timeline_uninit_mark(new_timeline_id, &timelines)?
+        };
        let new_metadata = TimelineMetadata::new(
            // Initialize disk_consistent LSN to 0, The caller must import some data to
            // make it valid, before calling finish_creation()
@@ -1476,6 +1476,7 @@ impl Tenant {
            initdb_lsn,
            None,
        )
+        .await
    }

    /// Helper for unit tests to create an empty timeline.
@@ -1491,7 +1492,9 @@ impl Tenant {
        pg_version: u32,
        ctx: &RequestContext,
    ) -> anyhow::Result<Arc<Timeline>> {
-        let uninit_tl = self.create_empty_timeline(new_timeline_id, initdb_lsn, pg_version, ctx)?;
+        let uninit_tl = self
+            .create_empty_timeline(new_timeline_id, initdb_lsn, pg_version, ctx)
+            .await?;
        let tline = uninit_tl.raw_timeline().expect("we just created it");
        assert_eq!(tline.get_last_record_lsn(), Lsn(0));

@@ -1501,7 +1504,7 @@ impl Tenant {
            .init_empty_test_timeline()
            .context("init_empty_test_timeline")?;
        modification
-            .commit()
+            .commit(ctx)
            .await
            .context("commit init_empty_test_timeline modification")?;

@@ -1509,6 +1512,15 @@ impl Tenant {
        tline.maybe_spawn_flush_loop();
        tline.freeze_and_flush().await.context("freeze_and_flush")?;

+        // Make sure the freeze_and_flush reaches remote storage.
+        tline
+            .remote_client
+            .as_ref()
+            .unwrap()
+            .wait_completion()
+            .await
+            .unwrap();
+
        let tl = uninit_tl.finish_creation()?;
        // The non-test code would call tl.activate() here.
        tl.set_state(TimelineState::Active);
@@ -1685,65 +1697,6 @@ impl Tenant {
        Ok(())
    }

-    /// Flush all in-memory data to disk and remote storage, if any.
-    ///
-    /// Used at graceful shutdown.
-    async fn freeze_and_flush_on_shutdown(&self) {
-        let mut js = tokio::task::JoinSet::new();
-
-        // execute on each timeline on the JoinSet, join after.
-        let per_timeline = |timeline_id: TimelineId, timeline: Arc<Timeline>| {
-            async move {
-                debug_assert_current_span_has_tenant_and_timeline_id();
-
-                match timeline.freeze_and_flush().await {
-                    Ok(()) => {}
-                    Err(e) => {
-                        warn!("failed to freeze and flush: {e:#}");
-                        return;
-                    }
-                }
-
-                let res = if let Some(client) = timeline.remote_client.as_ref() {
-                    // if we did not wait for completion here, it might be our shutdown process
-                    // didn't wait for remote uploads to complete at all, as new tasks can forever
-                    // be spawned.
-                    //
-                    // what is problematic is the shutting down of RemoteTimelineClient, because
-                    // obviously it does not make sense to stop while we wait for it, but what
-                    // about corner cases like s3 suddenly hanging up?
-                    client.wait_completion().await
-                } else {
-                    Ok(())
-                };
-
-                if let Err(e) = res {
-                    warn!("failed to await for frozen and flushed uploads: {e:#}");
-                }
-            }
-            .instrument(tracing::info_span!("freeze_and_flush_on_shutdown", %timeline_id))
-        };
-
-        {
-            let timelines = self.timelines.lock().unwrap();
-            timelines
-                .iter()
-                .map(|(id, tl)| (*id, Arc::clone(tl)))
-                .for_each(|(timeline_id, timeline)| {
-                    js.spawn(per_timeline(timeline_id, timeline));
-                })
-        };
-
-        while let Some(res) = js.join_next().await {
-            match res {
-                Ok(()) => {}
-                Err(je) if je.is_cancelled() => unreachable!("no cancelling used"),
-                Err(je) if je.is_panic() => { /* logged already */ }
-                Err(je) => warn!("unexpected JoinError: {je:?}"),
-            }
-        }
-    }
-
    pub fn current_state(&self) -> TenantState {
        self.state.borrow().clone()
    }
@@ -1874,19 +1827,22 @@ impl Tenant {
            }
        };

-        if freeze_and_flush {
-            // walreceiver has already began to shutdown with TenantState::Stopping, but we need to
-            // await for them to stop.
-            task_mgr::shutdown_tasks(
-                Some(TaskKind::WalReceiverManager),
-                Some(self.tenant_id),
-                None,
-            )
-            .await;
-
-            // this will wait for uploads to complete; in the past, it was done outside tenant
-            // shutdown in pageserver::shutdown_pageserver.
-            self.freeze_and_flush_on_shutdown().await;
+        let mut js = tokio::task::JoinSet::new();
+        {
+            let timelines = self.timelines.lock().unwrap();
+            timelines.values().for_each(|timeline| {
+                let timeline = Arc::clone(timeline);
+                let span = Span::current();
+                js.spawn(async move { timeline.shutdown(freeze_and_flush).instrument(span).await });
+            })
+        };
+        while let Some(res) = js.join_next().await {
+            match res {
+                Ok(()) => {}
+                Err(je) if je.is_cancelled() => unreachable!("no cancelling used"),
+                Err(je) if je.is_panic() => { /* logged already */ }
+                Err(je) => warn!("unexpected JoinError: {je:?}"),
+            }
        }

        // shutdown all tenant and timeline tasks: gc, compaction, page service
@@ -2274,6 +2230,7 @@ impl Tenant {
            ancestor,
            new_timeline_id,
            self.tenant_id,
+            self.generation,
            Arc::clone(&self.walredo_mgr),
            resources,
            pg_version,
@@ -2291,6 +2248,7 @@ impl Tenant {
        tenant_conf: TenantConfOpt,
        walredo_mgr: Arc<dyn WalRedoManager + Send + Sync>,
        tenant_id: TenantId,
+        generation: Generation,
        remote_storage: Option<GenericRemoteStorage>,
    ) -> Tenant {
        let (state, mut rx) = watch::channel(state);
@@ -2349,6 +2307,7 @@ impl Tenant {

        Tenant {
            tenant_id,
+            generation,
            conf,
            // using now here is good enough approximation to catch tenants with really long
            // activation times.
@@ -2410,72 +2369,37 @@ impl Tenant {
        Ok(tenant_conf)
    }

-    pub(super) fn persist_tenant_config(
+    #[tracing::instrument(skip_all, fields(%tenant_id))]
+    pub(super) async fn persist_tenant_config(
        tenant_id: &TenantId,
        target_config_path: &Path,
        tenant_conf: TenantConfOpt,
-        creating_tenant: bool,
    ) -> anyhow::Result<()> {
-        let _enter = info_span!("saving tenantconf").entered();
-
        // imitate a try-block with a closure
-        let do_persist = |target_config_path: &Path| -> anyhow::Result<()> {
-            let target_config_parent = target_config_path.parent().with_context(|| {
-                format!(
-                    "Config path does not have a parent: {}",
-                    target_config_path.display()
-                )
-            })?;
+        info!("persisting tenantconf to {}", target_config_path.display());

-            info!("persisting tenantconf to {}", target_config_path.display());
-
-            let mut conf_content = r#"# This file contains a specific per-tenant's config.
+        let mut conf_content = r#"# This file contains a specific per-tenant's config.
 #  It is read in case of pageserver restart.

 [tenant_config]
 "#
-            .to_string();
+        .to_string();

-            // Convert the config to a toml file.
-            conf_content += &toml_edit::ser::to_string(&tenant_conf)?;
+        // Convert the config to a toml file.
+        conf_content += &toml_edit::ser::to_string(&tenant_conf)?;

-            let mut target_config_file = VirtualFile::open_with_options(
-                target_config_path,
-                OpenOptions::new()
-                    .truncate(true) // This needed for overwriting with small config files
-                    .write(true)
-                    .create_new(creating_tenant)
-                    // when creating a new tenant, first_save will be true and `.create(true)` will be
-                    // ignored (per rust std docs).
-                    //
-                    // later when updating the config of created tenant, or persisting config for the
-                    // first time for attached tenant, the `.create(true)` is used.
-                    .create(true),
-            )?;
+        let conf_content = conf_content.as_bytes();

-            target_config_file
-                .write(conf_content.as_bytes())
-                .context("write toml bytes into file")
-                .and_then(|_| target_config_file.sync_all().context("fsync config file"))
-                .context("write config file")?;
-
-            // fsync the parent directory to ensure the directory entry is durable.
-            // before this was done conditionally on creating_tenant, but these management actions are rare
-            // enough to just fsync it always.
-
-            crashsafe::fsync(target_config_parent)?;
-            // XXX we're not fsyncing the parent dir, need to do that in case `creating_tenant`
-            Ok(())
-        };
-
-        // this function is called from creating the tenant and updating the tenant config, which
-        // would otherwise share this context, so keep it here in one place.
-        do_persist(target_config_path).with_context(|| {
-            format!(
-                "write tenant {tenant_id} config to {}",
-                target_config_path.display()
-            )
-        })
+        let temp_path = path_with_suffix_extension(target_config_path, TEMP_FILE_SUFFIX);
+        VirtualFile::crashsafe_overwrite(target_config_path, &temp_path, conf_content)
+            .await
+            .with_context(|| {
+                format!(
+                    "write tenant {tenant_id} config to {}",
+                    target_config_path.display()
+                )
+            })?;
+        Ok(())
    }

    //
@@ -2786,13 +2710,15 @@ impl Tenant {
            src_timeline.pg_version,
        );

-        let uninitialized_timeline = self.prepare_new_timeline(
-            dst_id,
-            &metadata,
-            timeline_uninit_mark,
-            start_lsn + 1,
-            Some(Arc::clone(src_timeline)),
-        )?;
+        let uninitialized_timeline = self
+            .prepare_new_timeline(
+                dst_id,
+                &metadata,
+                timeline_uninit_mark,
+                start_lsn + 1,
+                Some(Arc::clone(src_timeline)),
+            )
+            .await?;

        let new_timeline = uninitialized_timeline.finish_creation()?;

@@ -2870,13 +2796,15 @@ impl Tenant {
            pgdata_lsn,
            pg_version,
        );
-        let raw_timeline = self.prepare_new_timeline(
-            timeline_id,
-            &new_metadata,
-            timeline_uninit_mark,
-            pgdata_lsn,
-            None,
-        )?;
+        let raw_timeline = self
+            .prepare_new_timeline(
+                timeline_id,
+                &new_metadata,
+                timeline_uninit_mark,
+                pgdata_lsn,
+                None,
+            )
+            .await?;

        let tenant_id = raw_timeline.owning_tenant.tenant_id;
        let unfinished_timeline = raw_timeline.raw_timeline()?;
@@ -2931,6 +2859,7 @@ impl Tenant {
                self.conf,
                self.tenant_id,
                timeline_id,
+                self.generation,
            );
            Some(remote_client)
        } else {
@@ -2946,7 +2875,7 @@ impl Tenant {
    /// at 'disk_consistent_lsn'. After any initial data has been imported, call
    /// `finish_creation` to insert the Timeline into the timelines map and to remove the
    /// uninit mark file.
-    fn prepare_new_timeline(
+    async fn prepare_new_timeline(
        &self,
        new_timeline_id: TimelineId,
        new_metadata: &TimelineMetadata,
@@ -2974,8 +2903,9 @@ impl Tenant {

        timeline_struct.init_empty_layer_map(start_lsn);

-        if let Err(e) =
-            self.create_timeline_files(&uninit_mark.timeline_path, &new_timeline_id, new_metadata)
+        if let Err(e) = self
+            .create_timeline_files(&uninit_mark.timeline_path, &new_timeline_id, new_metadata)
+            .await
        {
            error!("Failed to create initial files for timeline {tenant_id}/{new_timeline_id}, cleaning up: {e:?}");
            cleanup_timeline_directory(uninit_mark);
@@ -2991,7 +2921,7 @@ impl Tenant {
        ))
    }

-    fn create_timeline_files(
+    async fn create_timeline_files(
        &self,
        timeline_path: &Path,
        new_timeline_id: &TimelineId,
@@ -3003,14 +2933,9 @@ impl Tenant {
            anyhow::bail!("failpoint after-timeline-uninit-mark-creation");
        });

-        save_metadata(
-            self.conf,
-            &self.tenant_id,
-            new_timeline_id,
-            new_metadata,
-            true,
-        )
-        .context("Failed to create timeline metadata")?;
+        save_metadata(self.conf, &self.tenant_id, new_timeline_id, new_metadata)
+            .await
+            .context("Failed to create timeline metadata")?;
        Ok(())
    }

@@ -3157,7 +3082,7 @@ pub(crate) enum CreateTenantFilesMode {
    Attach,
 }

-pub(crate) fn create_tenant_files(
+pub(crate) async fn create_tenant_files(
    conf: &'static PageServerConf,
    tenant_conf: TenantConfOpt,
    tenant_id: &TenantId,
@@ -3193,7 +3118,8 @@ pub(crate) fn create_tenant_files(
        mode,
        &temporary_tenant_dir,
        &target_tenant_directory,
-    );
+    )
+    .await;

    if creation_result.is_err() {
        error!("Failed to create directory structure for tenant {tenant_id}, cleaning tmp data");
@@ -3211,7 +3137,7 @@ pub(crate) fn create_tenant_files(
    Ok(target_tenant_directory)
 }

-fn try_create_target_tenant_dir(
+async fn try_create_target_tenant_dir(
    conf: &'static PageServerConf,
    tenant_conf: TenantConfOpt,
    tenant_id: &TenantId,
@@ -3250,7 +3176,7 @@ fn try_create_target_tenant_dir(
    )
    .with_context(|| format!("resolve tenant {tenant_id} temporary config path"))?;

-    Tenant::persist_tenant_config(tenant_id, &temporary_tenant_config_path, tenant_conf, true)?;
+    Tenant::persist_tenant_config(tenant_id, &temporary_tenant_config_path, tenant_conf).await?;

    crashsafe::create_dir(&temporary_tenant_timelines_dir).with_context(|| {
        format!(
@@ -3454,6 +3380,9 @@ pub mod harness {
        pub conf: &'static PageServerConf,
        pub tenant_conf: TenantConf,
        pub tenant_id: TenantId,
+        pub generation: Generation,
+        pub remote_storage: GenericRemoteStorage,
+        pub remote_fs_dir: PathBuf,
    }

    static LOG_HANDLE: OnceCell<()> = OnceCell::new();
@@ -3491,28 +3420,39 @@ pub mod harness {
            fs::create_dir_all(conf.tenant_path(&tenant_id))?;
            fs::create_dir_all(conf.timelines_path(&tenant_id))?;

+            use remote_storage::{RemoteStorageConfig, RemoteStorageKind};
+            let remote_fs_dir = conf.workdir.join("localfs");
+            std::fs::create_dir_all(&remote_fs_dir).unwrap();
+            let config = RemoteStorageConfig {
+                // TODO: why not remote_storage::DEFAULT_REMOTE_STORAGE_MAX_CONCURRENT_SYNCS,
+                max_concurrent_syncs: std::num::NonZeroUsize::new(2_000_000).unwrap(),
+                // TODO: why not remote_storage::DEFAULT_REMOTE_STORAGE_MAX_SYNC_ERRORS,
+                max_sync_errors: std::num::NonZeroU32::new(3_000_000).unwrap(),
+                storage: RemoteStorageKind::LocalFs(remote_fs_dir.clone()),
+            };
+            let remote_storage = GenericRemoteStorage::from_config(&config).unwrap();
+
            Ok(Self {
                conf,
                tenant_conf,
                tenant_id,
+                generation: Generation::new(0xdeadbeef),
+                remote_storage,
+                remote_fs_dir,
            })
        }

        pub async fn load(&self) -> (Arc<Tenant>, RequestContext) {
            let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);
            (
-                self.try_load(&ctx, None)
+                self.try_load(&ctx)
                    .await
                    .expect("failed to load test tenant"),
                ctx,
            )
        }

-        pub async fn try_load(
-            &self,
-            ctx: &RequestContext,
-            remote_storage: Option<remote_storage::GenericRemoteStorage>,
-        ) -> anyhow::Result<Arc<Tenant>> {
+        pub async fn try_load(&self, ctx: &RequestContext) -> anyhow::Result<Arc<Tenant>> {
            let walredo_mgr = Arc::new(TestRedoManager);

            let tenant = Arc::new(Tenant::new(
@@ -3521,7 +3461,8 @@ pub mod harness {
                TenantConfOpt::from(self.tenant_conf),
                walredo_mgr,
                self.tenant_id,
-                remote_storage,
+                self.generation,
+                Some(self.remote_storage.clone()),
            ));
            tenant
                .load(None, ctx)
@@ -3597,14 +3538,24 @@ mod tests {

        let writer = tline.writer().await;
        writer
-            .put(*TEST_KEY, Lsn(0x10), &Value::Image(TEST_IMG("foo at 0x10")))
+            .put(
+                *TEST_KEY,
+                Lsn(0x10),
+                &Value::Image(TEST_IMG("foo at 0x10")),
+                &ctx,
+            )
            .await?;
        writer.finish_write(Lsn(0x10));
        drop(writer);

        let writer = tline.writer().await;
        writer
-            .put(*TEST_KEY, Lsn(0x20), &Value::Image(TEST_IMG("foo at 0x20")))
+            .put(
+                *TEST_KEY,
+                Lsn(0x20),
+                &Value::Image(TEST_IMG("foo at 0x20")),
+                &ctx,
+            )
            .await?;
        writer.finish_write(Lsn(0x20));
        drop(writer);
@@ -3634,7 +3585,10 @@ mod tests {
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;

-        match tenant.create_empty_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx) {
+        match tenant
+            .create_empty_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
+            .await
+        {
            Ok(_) => panic!("duplicate timeline creation should fail"),
            Err(e) => assert_eq!(
                e.to_string(),
@@ -3675,19 +3629,19 @@ mod tests {

        // Insert a value on the timeline
        writer
-            .put(TEST_KEY_A, Lsn(0x20), &test_value("foo at 0x20"))
+            .put(TEST_KEY_A, Lsn(0x20), &test_value("foo at 0x20"), &ctx)
            .await?;
        writer
-            .put(TEST_KEY_B, Lsn(0x20), &test_value("foobar at 0x20"))
+            .put(TEST_KEY_B, Lsn(0x20), &test_value("foobar at 0x20"), &ctx)
            .await?;
        writer.finish_write(Lsn(0x20));

        writer
-            .put(TEST_KEY_A, Lsn(0x30), &test_value("foo at 0x30"))
+            .put(TEST_KEY_A, Lsn(0x30), &test_value("foo at 0x30"), &ctx)
            .await?;
        writer.finish_write(Lsn(0x30));
        writer
-            .put(TEST_KEY_A, Lsn(0x40), &test_value("foo at 0x40"))
+            .put(TEST_KEY_A, Lsn(0x40), &test_value("foo at 0x40"), &ctx)
            .await?;
        writer.finish_write(Lsn(0x40));

@@ -3702,7 +3656,7 @@ mod tests {
            .expect("Should have a local timeline");
        let new_writer = newtline.writer().await;
        new_writer
-            .put(TEST_KEY_A, Lsn(0x40), &test_value("bar at 0x40"))
+            .put(TEST_KEY_A, Lsn(0x40), &test_value("bar at 0x40"), &ctx)
            .await?;
        new_writer.finish_write(Lsn(0x40));

@@ -3725,7 +3679,11 @@ mod tests {
        Ok(())
    }

-    async fn make_some_layers(tline: &Timeline, start_lsn: Lsn) -> anyhow::Result<()> {
+    async fn make_some_layers(
+        tline: &Timeline,
+        start_lsn: Lsn,
+        ctx: &RequestContext,
+    ) -> anyhow::Result<()> {
        let mut lsn = start_lsn;
        #[allow(non_snake_case)]
        {
@@ -3736,6 +3694,7 @@ mod tests {
                    *TEST_KEY,
                    lsn,
                    &Value::Image(TEST_IMG(&format!("foo at {}", lsn))),
+                    ctx,
                )
                .await?;
            writer.finish_write(lsn);
@@ -3745,6 +3704,7 @@ mod tests {
                    *TEST_KEY,
                    lsn,
                    &Value::Image(TEST_IMG(&format!("foo at {}", lsn))),
+                    ctx,
                )
                .await?;
            writer.finish_write(lsn);
@@ -3758,6 +3718,7 @@ mod tests {
                    *TEST_KEY,
                    lsn,
                    &Value::Image(TEST_IMG(&format!("foo at {}", lsn))),
+                    ctx,
                )
                .await?;
            writer.finish_write(lsn);
@@ -3767,6 +3728,7 @@ mod tests {
                    *TEST_KEY,
                    lsn,
                    &Value::Image(TEST_IMG(&format!("foo at {}", lsn))),
+                    ctx,
                )
                .await?;
            writer.finish_write(lsn);
@@ -3783,7 +3745,7 @@ mod tests {
        let tline = tenant
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;
-        make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+        make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

        // this removes layers before lsn 40 (50 minus 10), so there are two remaining layers, image and delta for 31-50
        // FIXME: this doesn't actually remove any layer currently, given how the flushing
@@ -3857,7 +3819,7 @@ mod tests {
            .load();

        let tline = repo.create_empty_timeline(TIMELINE_ID, Lsn(0), DEFAULT_PG_VERSION)?;
-        make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+        make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

        repo.gc_iteration(Some(TIMELINE_ID), 0x10, Duration::ZERO)?;
        let latest_gc_cutoff_lsn = tline.get_latest_gc_cutoff_lsn();
@@ -3879,7 +3841,7 @@ mod tests {
        let tline = tenant
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;
-        make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+        make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

        tenant
            .branch_timeline_test(&tline, NEW_TIMELINE_ID, Some(Lsn(0x40)), &ctx)
@@ -3888,7 +3850,7 @@ mod tests {
            .get_timeline(NEW_TIMELINE_ID, true)
            .expect("Should have a local timeline");

-        make_some_layers(newtline.as_ref(), Lsn(0x60)).await?;
+        make_some_layers(newtline.as_ref(), Lsn(0x60), &ctx).await?;

        tline.set_broken("test".to_owned());

@@ -3929,7 +3891,7 @@ mod tests {
        let tline = tenant
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;
-        make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+        make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

        tenant
            .branch_timeline_test(&tline, NEW_TIMELINE_ID, Some(Lsn(0x40)), &ctx)
@@ -3954,7 +3916,7 @@ mod tests {
        let tline = tenant
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;
-        make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+        make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

        tenant
            .branch_timeline_test(&tline, NEW_TIMELINE_ID, Some(Lsn(0x40)), &ctx)
@@ -3963,7 +3925,7 @@ mod tests {
            .get_timeline(NEW_TIMELINE_ID, true)
            .expect("Should have a local timeline");

-        make_some_layers(newtline.as_ref(), Lsn(0x60)).await?;
+        make_some_layers(newtline.as_ref(), Lsn(0x60), &ctx).await?;

        // run gc on parent
        tenant
@@ -3988,7 +3950,14 @@ mod tests {
            let tline = tenant
                .create_test_timeline(TIMELINE_ID, Lsn(0x7000), DEFAULT_PG_VERSION, &ctx)
                .await?;
-            make_some_layers(tline.as_ref(), Lsn(0x8000)).await?;
+            make_some_layers(tline.as_ref(), Lsn(0x8000), &ctx).await?;
+            // so that all uploads finish & we can call harness.load() below again
+            tenant
+                .shutdown(Default::default(), true)
+                .instrument(info_span!("test_shutdown", tenant_id=%tenant.tenant_id))
+                .await
+                .ok()
+                .unwrap();
        }

        let (tenant, _ctx) = harness.load().await;
@@ -4010,7 +3979,7 @@ mod tests {
                .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
                .await?;

-            make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+            make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

            let child_tline = tenant
                .branch_timeline_test(&tline, NEW_TIMELINE_ID, Some(Lsn(0x40)), &ctx)
@@ -4021,7 +3990,15 @@ mod tests {
                .get_timeline(NEW_TIMELINE_ID, true)
                .expect("Should have a local timeline");

-            make_some_layers(newtline.as_ref(), Lsn(0x60)).await?;
+            make_some_layers(newtline.as_ref(), Lsn(0x60), &ctx).await?;
+
+            // so that all uploads finish & we can call harness.load() below again
+            tenant
+                .shutdown(Default::default(), true)
+                .instrument(info_span!("test_shutdown", tenant_id=%tenant.tenant_id))
+                .await
+                .ok()
+                .unwrap();
        }

        // check that both of them are initially unloaded
@@ -4045,7 +4022,7 @@ mod tests {
        let tline = tenant
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;
-        make_some_layers(tline.as_ref(), Lsn(0x20)).await?;
+        make_some_layers(tline.as_ref(), Lsn(0x20), &ctx).await?;

        let layer_map = tline.layers.read().await;
        let level0_deltas = layer_map.layer_map().get_level0_deltas()?;
@@ -4074,6 +4051,13 @@ mod tests {
            .create_test_timeline(TIMELINE_ID, Lsn(0x10), DEFAULT_PG_VERSION, &ctx)
            .await?;
        drop(tline);
+        // so that all uploads finish & we can call harness.try_load() below again
+        tenant
+            .shutdown(Default::default(), true)
+            .instrument(info_span!("test_shutdown", tenant_id=%tenant.tenant_id))
+            .await
+            .ok()
+            .unwrap();
        drop(tenant);

        let metadata_path = harness.timeline_path(&TIMELINE_ID).join(METADATA_FILE_NAME);
@@ -4085,11 +4069,7 @@ mod tests {
        metadata_bytes[8] ^= 1;
        std::fs::write(metadata_path, metadata_bytes)?;

-        let err = harness
-            .try_load(&ctx, None)
-            .await
-            .err()
-            .expect("should fail");
+        let err = harness.try_load(&ctx).await.err().expect("should fail");
        // get all the stack with all .context, not only the last one
        let message = format!("{err:#}");
        let expected = "failed to load metadata";
@@ -4125,7 +4105,12 @@ mod tests {

        let writer = tline.writer().await;
        writer
-            .put(*TEST_KEY, Lsn(0x10), &Value::Image(TEST_IMG("foo at 0x10")))
+            .put(
+                *TEST_KEY,
+                Lsn(0x10),
+                &Value::Image(TEST_IMG("foo at 0x10")),
+                &ctx,
+            )
            .await?;
        writer.finish_write(Lsn(0x10));
        drop(writer);
@@ -4135,7 +4120,12 @@ mod tests {

        let writer = tline.writer().await;
        writer
-            .put(*TEST_KEY, Lsn(0x20), &Value::Image(TEST_IMG("foo at 0x20")))
+            .put(
+                *TEST_KEY,
+                Lsn(0x20),
+                &Value::Image(TEST_IMG("foo at 0x20")),
+                &ctx,
+            )
            .await?;
        writer.finish_write(Lsn(0x20));
        drop(writer);
@@ -4145,7 +4135,12 @@ mod tests {

        let writer = tline.writer().await;
        writer
-            .put(*TEST_KEY, Lsn(0x30), &Value::Image(TEST_IMG("foo at 0x30")))
+            .put(
+                *TEST_KEY,
+                Lsn(0x30),
+                &Value::Image(TEST_IMG("foo at 0x30")),
+                &ctx,
+            )
            .await?;
        writer.finish_write(Lsn(0x30));
        drop(writer);
@@ -4155,7 +4150,12 @@ mod tests {

        let writer = tline.writer().await;
        writer
-            .put(*TEST_KEY, Lsn(0x40), &Value::Image(TEST_IMG("foo at 0x40")))
+            .put(
+                *TEST_KEY,
+                Lsn(0x40),
+                &Value::Image(TEST_IMG("foo at 0x40")),
+                &ctx,
+            )
            .await?;
        writer.finish_write(Lsn(0x40));
        drop(writer);
@@ -4213,6 +4213,7 @@ mod tests {
                        test_key,
                        lsn,
                        &Value::Image(TEST_IMG(&format!("{} at {}", blknum, lsn))),
+                        &ctx,
                    )
                    .await?;
                writer.finish_write(lsn);
@@ -4265,6 +4266,7 @@ mod tests {
                    test_key,
                    lsn,
                    &Value::Image(TEST_IMG(&format!("{} at {}", blknum, lsn))),
+                    &ctx,
                )
                .await?;
            writer.finish_write(lsn);
@@ -4285,6 +4287,7 @@ mod tests {
                        test_key,
                        lsn,
                        &Value::Image(TEST_IMG(&format!("{} at {}", blknum, lsn))),
+                        &ctx,
                    )
                    .await?;
                writer.finish_write(lsn);
@@ -4344,6 +4347,7 @@ mod tests {
                    test_key,
                    lsn,
                    &Value::Image(TEST_IMG(&format!("{} at {}", blknum, lsn))),
+                    &ctx,
                )
                .await?;
            writer.finish_write(lsn);
@@ -4372,6 +4376,7 @@ mod tests {
                        test_key,
                        lsn,
                        &Value::Image(TEST_IMG(&format!("{} at {}", blknum, lsn))),
+                        &ctx,
                    )
                    .await?;
                println!("updating {} at {}", blknum, lsn);
@@ -4440,6 +4445,7 @@ mod tests {
                        test_key,
                        lsn,
                        &Value::Image(TEST_IMG(&format!("{} {} at {}", idx, blknum, lsn))),
+                        &ctx,
                    )
                    .await?;
                println!("updating [{}][{}] at {}", idx, blknum, lsn);
@@ -4474,8 +4480,9 @@ mod tests {
            .await;

        let initdb_lsn = Lsn(0x20);
-        let utline =
-            tenant.create_empty_timeline(TIMELINE_ID, initdb_lsn, DEFAULT_PG_VERSION, &ctx)?;
+        let utline = tenant
+            .create_empty_timeline(TIMELINE_ID, initdb_lsn, DEFAULT_PG_VERSION, &ctx)
+            .await?;
        let tline = utline.raw_timeline().unwrap();

        // Spawn flush loop now so that we can set the `expect_initdb_optimization`
@@ -4511,7 +4518,7 @@ mod tests {
            .init_empty_test_timeline()
            .context("init_empty_test_timeline")?;
        modification
-            .commit()
+            .commit(&ctx)
            .await
            .context("commit init_empty_test_timeline modification")?;

@@ -4540,9 +4547,15 @@ mod tests {
        let harness = TenantHarness::create(name)?;
        {
            let (tenant, ctx) = harness.load().await;
-            let tline =
-                tenant.create_empty_timeline(TIMELINE_ID, Lsn(0), DEFAULT_PG_VERSION, &ctx)?;
+            let tline = tenant
+                .create_empty_timeline(TIMELINE_ID, Lsn(0), DEFAULT_PG_VERSION, &ctx)
+                .await?;
            // Keeps uninit mark in place
+            let raw_tline = tline.raw_timeline().unwrap();
+            raw_tline
+                .shutdown(false)
+                .instrument(info_span!("test_shutdown", tenant_id=%raw_tline.tenant_id))
+                .await;
            std::mem::forget(tline);
        }

--- a/pageserver/src/tenant/blob_io.rs
+++ b/pageserver/src/tenant/blob_io.rs
@@ -11,16 +11,22 @@
 //! len <  128: 0XXXXXXX
 //! len >= 128: 1XXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
 //!
+use crate::context::RequestContext;
 use crate::page_cache::PAGE_SZ;
 use crate::tenant::block_io::BlockCursor;
+use crate::virtual_file::VirtualFile;
 use std::cmp::min;
 use std::io::{Error, ErrorKind};

 impl<'a> BlockCursor<'a> {
    /// Read a blob into a new buffer.
-    pub async fn read_blob(&self, offset: u64) -> Result<Vec<u8>, std::io::Error> {
+    pub async fn read_blob(
+        &self,
+        offset: u64,
+        ctx: &RequestContext,
+    ) -> Result<Vec<u8>, std::io::Error> {
        let mut buf = Vec::new();
-        self.read_blob_into_buf(offset, &mut buf).await?;
+        self.read_blob_into_buf(offset, &mut buf, ctx).await?;
        Ok(buf)
    }
    /// Read blob into the given buffer. Any previous contents in the buffer
@@ -29,11 +35,12 @@ impl<'a> BlockCursor<'a> {
        &self,
        offset: u64,
        dstbuf: &mut Vec<u8>,
+        ctx: &RequestContext,
    ) -> Result<(), std::io::Error> {
        let mut blknum = (offset / PAGE_SZ as u64) as u32;
        let mut off = (offset % PAGE_SZ as u64) as usize;

-        let mut buf = self.read_blk(blknum).await?;
+        let mut buf = self.read_blk(blknum, ctx).await?;

        // peek at the first byte, to determine if it's a 1- or 4-byte length
        let first_len_byte = buf[off];
@@ -49,7 +56,7 @@ impl<'a> BlockCursor<'a> {
                // it is split across two pages
                len_buf[..thislen].copy_from_slice(&buf[off..PAGE_SZ]);
                blknum += 1;
-                buf = self.read_blk(blknum).await?;
+                buf = self.read_blk(blknum, ctx).await?;
                len_buf[thislen..].copy_from_slice(&buf[0..4 - thislen]);
                off = 4 - thislen;
            } else {
@@ -70,7 +77,7 @@ impl<'a> BlockCursor<'a> {
            if page_remain == 0 {
                // continue on next page
                blknum += 1;
-                buf = self.read_blk(blknum).await?;
+                buf = self.read_blk(blknum, ctx).await?;
                off = 0;
                page_remain = PAGE_SZ;
            }
@@ -83,35 +90,24 @@ impl<'a> BlockCursor<'a> {
    }
 }

+/// A wrapper of `VirtualFile` that allows users to write blobs.
 ///
-/// Abstract trait for a data sink that you can write blobs to.
-///
-pub trait BlobWriter {
-    /// Write a blob of data. Returns the offset that it was written to,
-    /// which can be used to retrieve the data later.
-    fn write_blob(&mut self, srcbuf: &[u8]) -> Result<u64, Error>;
-}
-
-///
-/// An implementation of BlobWriter to write blobs to anything that
-/// implements std::io::Write.
-///
-pub struct WriteBlobWriter<W>
-where
-    W: std::io::Write,
-{
-    inner: W,
+/// If a `BlobWriter` is dropped, the internal buffer will be
+/// discarded. You need to call [`flush_buffer`](Self::flush_buffer)
+/// manually before dropping.
+pub struct BlobWriter<const BUFFERED: bool> {
+    inner: VirtualFile,
    offset: u64,
+    /// A buffer to save on write calls, only used if BUFFERED=true
+    buf: Vec<u8>,
 }

-impl<W> WriteBlobWriter<W>
-where
-    W: std::io::Write,
-{
-    pub fn new(inner: W, start_offset: u64) -> Self {
-        WriteBlobWriter {
+impl<const BUFFERED: bool> BlobWriter<BUFFERED> {
+    pub fn new(inner: VirtualFile, start_offset: u64) -> Self {
+        Self {
            inner,
            offset: start_offset,
+            buf: Vec::with_capacity(Self::CAPACITY),
        }
    }

@@ -119,28 +115,79 @@ where
        self.offset
    }

-    /// Access the underlying Write object.
-    ///
-    /// NOTE: WriteBlobWriter keeps track of the current write offset. If
-    /// you write something directly to the inner Write object, it makes the
-    /// internally tracked 'offset' to go out of sync. So don't do that.
-    pub fn into_inner(self) -> W {
-        self.inner
-    }
-}
+    const CAPACITY: usize = if BUFFERED { PAGE_SZ } else { 0 };

-impl<W> BlobWriter for WriteBlobWriter<W>
-where
-    W: std::io::Write,
-{
-    fn write_blob(&mut self, srcbuf: &[u8]) -> Result<u64, Error> {
+    #[inline(always)]
+    /// Writes the given buffer directly to the underlying `VirtualFile`.
+    /// You need to make sure that the internal buffer is empty, otherwise
+    /// data will be written in wrong order.
+    async fn write_all_unbuffered(&mut self, src_buf: &[u8]) -> Result<(), Error> {
+        self.inner.write_all(src_buf).await?;
+        self.offset += src_buf.len() as u64;
+        Ok(())
+    }
+
+    #[inline(always)]
+    /// Flushes the internal buffer to the underlying `VirtualFile`.
+    pub async fn flush_buffer(&mut self) -> Result<(), Error> {
+        self.inner.write_all(&self.buf).await?;
+        self.buf.clear();
+        Ok(())
+    }
+
+    #[inline(always)]
+    /// Writes as much of `src_buf` into the internal buffer as it fits
+    fn write_into_buffer(&mut self, src_buf: &[u8]) -> usize {
+        let remaining = Self::CAPACITY - self.buf.len();
+        let to_copy = src_buf.len().min(remaining);
+        self.buf.extend_from_slice(&src_buf[..to_copy]);
+        self.offset += to_copy as u64;
+        to_copy
+    }
+
+    /// Internal, possibly buffered, write function
+    async fn write_all(&mut self, mut src_buf: &[u8]) -> Result<(), Error> {
+        if !BUFFERED {
+            assert!(self.buf.is_empty());
+            self.write_all_unbuffered(src_buf).await?;
+            return Ok(());
+        }
+        let remaining = Self::CAPACITY - self.buf.len();
+        // First try to copy as much as we can into the buffer
+        if remaining > 0 {
+            let copied = self.write_into_buffer(src_buf);
+            src_buf = &src_buf[copied..];
+        }
+        // Then, if the buffer is full, flush it out
+        if self.buf.len() == Self::CAPACITY {
+            self.flush_buffer().await?;
+        }
+        // Finally, write the tail of src_buf:
+        // If it wholly fits into the buffer without
+        // completely filling it, then put it there.
+        // If not, write it out directly.
+        if !src_buf.is_empty() {
+            assert_eq!(self.buf.len(), 0);
+            if src_buf.len() < Self::CAPACITY {
+                let copied = self.write_into_buffer(src_buf);
+                // We just verified above that src_buf fits into our internal buffer.
+                assert_eq!(copied, src_buf.len());
+            } else {
+                self.write_all_unbuffered(src_buf).await?;
+            }
+        }
+        Ok(())
+    }
+
+    /// Write a blob of data. Returns the offset that it was written to,
+    /// which can be used to retrieve the data later.
+    pub async fn write_blob(&mut self, srcbuf: &[u8]) -> Result<u64, Error> {
        let offset = self.offset;

        if srcbuf.len() < 128 {
            // Short blob. Write a 1-byte length header
            let len_buf = srcbuf.len() as u8;
-            self.inner.write_all(&[len_buf])?;
-            self.offset += 1;
+            self.write_all(&[len_buf]).await?;
        } else {
            // Write a 4-byte length header
            if srcbuf.len() > 0x7fff_ffff {
@@ -151,11 +198,154 @@ where
            }
            let mut len_buf = ((srcbuf.len()) as u32).to_be_bytes();
            len_buf[0] |= 0x80;
-            self.inner.write_all(&len_buf)?;
-            self.offset += 4;
+            self.write_all(&len_buf).await?;
        }
-        self.inner.write_all(srcbuf)?;
-        self.offset += srcbuf.len() as u64;
+        self.write_all(srcbuf).await?;
        Ok(offset)
    }
 }
+
+impl BlobWriter<true> {
+    /// Access the underlying `VirtualFile`.
+    ///
+    /// This function flushes the internal buffer before giving access
+    /// to the underlying `VirtualFile`.
+    pub async fn into_inner(mut self) -> Result<VirtualFile, Error> {
+        self.flush_buffer().await?;
+        Ok(self.inner)
+    }
+
+    /// Access the underlying `VirtualFile`.
+    ///
+    /// Unlike [`into_inner`](Self::into_inner), this doesn't flush
+    /// the internal buffer before giving access.
+    pub fn into_inner_no_flush(self) -> VirtualFile {
+        self.inner
+    }
+}
+
+impl BlobWriter<false> {
+    /// Access the underlying `VirtualFile`.
+    pub fn into_inner(self) -> VirtualFile {
+        self.inner
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{context::DownloadBehavior, task_mgr::TaskKind, tenant::block_io::BlockReaderRef};
+    use rand::{Rng, SeedableRng};
+
+    async fn round_trip_test<const BUFFERED: bool>(blobs: &[Vec<u8>]) -> Result<(), Error> {
+        let temp_dir = tempfile::tempdir()?;
+        let path = temp_dir.path().join("file");
+        let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);
+
+        // Write part (in block to drop the file)
+        let mut offsets = Vec::new();
+        {
+            let file = VirtualFile::create(&path).await?;
+            let mut wtr = BlobWriter::<BUFFERED>::new(file, 0);
+            for blob in blobs.iter() {
+                let offs = wtr.write_blob(blob).await?;
+                offsets.push(offs);
+            }
+            // Write out one page worth of zeros so that we can
+            // read again with read_blk
+            let offs = wtr.write_blob(&vec![0; PAGE_SZ]).await?;
+            println!("Writing final blob at offs={offs}");
+            wtr.flush_buffer().await?;
+        }
+
+        let file = VirtualFile::open(&path).await?;
+        let rdr = BlockReaderRef::VirtualFile(&file);
+        let rdr = BlockCursor::new(rdr);
+        for (idx, (blob, offset)) in blobs.iter().zip(offsets.iter()).enumerate() {
+            let blob_read = rdr.read_blob(*offset, &ctx).await?;
+            assert_eq!(
+                blob, &blob_read,
+                "mismatch for idx={idx} at offset={offset}"
+            );
+        }
+        Ok(())
+    }
+
+    fn random_array(len: usize) -> Vec<u8> {
+        let mut rng = rand::thread_rng();
+        (0..len).map(|_| rng.gen()).collect::<_>()
+    }
+
+    #[tokio::test]
+    async fn test_one() -> Result<(), Error> {
+        let blobs = &[vec![12, 21, 22]];
+        round_trip_test::<false>(blobs).await?;
+        round_trip_test::<true>(blobs).await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_hello_simple() -> Result<(), Error> {
+        let blobs = &[
+            vec![0, 1, 2, 3],
+            b"Hello, World!".to_vec(),
+            Vec::new(),
+            b"foobar".to_vec(),
+        ];
+        round_trip_test::<false>(blobs).await?;
+        round_trip_test::<true>(blobs).await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_really_big_array() -> Result<(), Error> {
+        let blobs = &[
+            b"test".to_vec(),
+            random_array(10 * PAGE_SZ),
+            b"foobar".to_vec(),
+        ];
+        round_trip_test::<false>(blobs).await?;
+        round_trip_test::<true>(blobs).await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_arrays_inc() -> Result<(), Error> {
+        let blobs = (0..PAGE_SZ / 8)
+            .map(|v| random_array(v * 16))
+            .collect::<Vec<_>>();
+        round_trip_test::<false>(&blobs).await?;
+        round_trip_test::<true>(&blobs).await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_arrays_random_size() -> Result<(), Error> {
+        let mut rng = rand::rngs::StdRng::seed_from_u64(42);
+        let blobs = (0..1024)
+            .map(|_| {
+                let mut sz: u16 = rng.gen();
+                // Make 50% of the arrays small
+                if rng.gen() {
+                    sz |= 63;
+                }
+                random_array(sz.into())
+            })
+            .collect::<Vec<_>>();
+        round_trip_test::<false>(&blobs).await?;
+        round_trip_test::<true>(&blobs).await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_arrays_page_boundary() -> Result<(), Error> {
+        let blobs = &[
+            random_array(PAGE_SZ - 4),
+            random_array(PAGE_SZ - 4),
+            random_array(PAGE_SZ - 4),
+        ];
+        round_trip_test::<false>(blobs).await?;
+        round_trip_test::<true>(blobs).await?;
+        Ok(())
+    }
+}
--- a/pageserver/src/tenant/block_io.rs
+++ b/pageserver/src/tenant/block_io.rs
@@ -4,12 +4,11 @@

 use super::ephemeral_file::EphemeralFile;
 use super::storage_layer::delta_layer::{Adapter, DeltaLayerInner};
+use crate::context::RequestContext;
 use crate::page_cache::{self, PageReadGuard, ReadBufResult, PAGE_SZ};
 use crate::virtual_file::VirtualFile;
 use bytes::Bytes;
-use std::fs::File;
 use std::ops::{Deref, DerefMut};
-use std::os::unix::fs::FileExt;

 /// This is implemented by anything that can read 8 kB (PAGE_SZ)
 /// blocks, using the page cache
@@ -73,25 +72,31 @@ impl<'a> Deref for BlockLease<'a> {
 ///
 /// Unlike traits, we also support the read function to be async though.
 pub(crate) enum BlockReaderRef<'a> {
-    FileBlockReaderVirtual(&'a FileBlockReader<VirtualFile>),
-    FileBlockReaderFile(&'a FileBlockReader<std::fs::File>),
+    FileBlockReader(&'a FileBlockReader),
    EphemeralFile(&'a EphemeralFile),
    Adapter(Adapter<&'a DeltaLayerInner>),
    #[cfg(test)]
    TestDisk(&'a super::disk_btree::tests::TestDisk),
+    #[cfg(test)]
+    VirtualFile(&'a VirtualFile),
 }

 impl<'a> BlockReaderRef<'a> {
    #[inline(always)]
-    async fn read_blk(&self, blknum: u32) -> Result<BlockLease, std::io::Error> {
+    async fn read_blk(
+        &self,
+        blknum: u32,
+        ctx: &RequestContext,
+    ) -> Result<BlockLease, std::io::Error> {
        use BlockReaderRef::*;
        match self {
-            FileBlockReaderVirtual(r) => r.read_blk(blknum).await,
-            FileBlockReaderFile(r) => r.read_blk(blknum).await,
-            EphemeralFile(r) => r.read_blk(blknum).await,
-            Adapter(r) => r.read_blk(blknum).await,
+            FileBlockReader(r) => r.read_blk(blknum, ctx).await,
+            EphemeralFile(r) => r.read_blk(blknum, ctx).await,
+            Adapter(r) => r.read_blk(blknum, ctx).await,
            #[cfg(test)]
            TestDisk(r) => r.read_blk(blknum),
+            #[cfg(test)]
+            VirtualFile(r) => r.read_blk(blknum).await,
        }
    }
 }
@@ -105,11 +110,13 @@ impl<'a> BlockReaderRef<'a> {
 ///
 /// ```no_run
 /// # use pageserver::tenant::block_io::{BlockReader, FileBlockReader};
-/// # let reader: FileBlockReader<std::fs::File> = unimplemented!("stub");
+/// # use pageserver::context::RequestContext;
+/// # let reader: FileBlockReader = unimplemented!("stub");
+/// # let ctx: RequestContext = unimplemented!("stub");
 /// let cursor = reader.block_cursor();
-/// let buf = cursor.read_blk(1);
+/// let buf = cursor.read_blk(1, &ctx);
 /// // do stuff with 'buf'
-/// let buf = cursor.read_blk(2);
+/// let buf = cursor.read_blk(2, &ctx);
 /// // do stuff with 'buf'
 /// ```
 ///
@@ -122,9 +129,9 @@ impl<'a> BlockCursor<'a> {
        BlockCursor { reader }
    }
    // Needed by cli
-    pub fn new_fileblockreader_virtual(reader: &'a FileBlockReader<VirtualFile>) -> Self {
+    pub fn new_fileblockreader(reader: &'a FileBlockReader) -> Self {
        BlockCursor {
-            reader: BlockReaderRef::FileBlockReaderVirtual(reader),
+            reader: BlockReaderRef::FileBlockReader(reader),
        }
    }

@@ -134,8 +141,12 @@ impl<'a> BlockCursor<'a> {
    /// access to the contents of the page. (For the page cache, the
    /// lease object represents a lock on the buffer.)
    #[inline(always)]
-    pub async fn read_blk(&self, blknum: u32) -> Result<BlockLease, std::io::Error> {
-        self.reader.read_blk(blknum).await
+    pub async fn read_blk(
+        &self,
+        blknum: u32,
+        ctx: &RequestContext,
+    ) -> Result<BlockLease, std::io::Error> {
+        self.reader.read_blk(blknum, ctx).await
    }
 }

@@ -143,38 +154,41 @@ impl<'a> BlockCursor<'a> {
 ///
 /// The file is assumed to be immutable. This doesn't provide any functions
 /// for modifying the file, nor for invalidating the cache if it is modified.
-pub struct FileBlockReader<F> {
-    pub file: F,
+pub struct FileBlockReader {
+    pub file: VirtualFile,

    /// Unique ID of this file, used as key in the page cache.
    file_id: page_cache::FileId,
 }

-impl<F> FileBlockReader<F>
-where
-    F: FileExt,
-{
-    pub fn new(file: F) -> Self {
+impl FileBlockReader {
+    pub fn new(file: VirtualFile) -> Self {
        let file_id = page_cache::next_file_id();

        FileBlockReader { file_id, file }
    }

    /// Read a page from the underlying file into given buffer.
-    fn fill_buffer(&self, buf: &mut [u8], blkno: u32) -> Result<(), std::io::Error> {
+    async fn fill_buffer(&self, buf: &mut [u8], blkno: u32) -> Result<(), std::io::Error> {
        assert!(buf.len() == PAGE_SZ);
-        self.file.read_exact_at(buf, blkno as u64 * PAGE_SZ as u64)
+        self.file
+            .read_exact_at(buf, blkno as u64 * PAGE_SZ as u64)
+            .await
    }
    /// Read a block.
    ///
    /// Returns a "lease" object that can be used to
    /// access to the contents of the page. (For the page cache, the
    /// lease object represents a lock on the buffer.)
-    pub async fn read_blk(&self, blknum: u32) -> Result<BlockLease, std::io::Error> {
+    pub async fn read_blk(
+        &self,
+        blknum: u32,
+        ctx: &RequestContext,
+    ) -> Result<BlockLease, std::io::Error> {
        let cache = page_cache::get();
        loop {
            match cache
-                .read_immutable_buf(self.file_id, blknum)
+                .read_immutable_buf(self.file_id, blknum, ctx)
                .await
                .map_err(|e| {
                    std::io::Error::new(
@@ -185,7 +199,7 @@ where
                ReadBufResult::Found(guard) => break Ok(guard.into()),
                ReadBufResult::NotFound(mut write_guard) => {
                    // Read the page from disk into the buffer
-                    self.fill_buffer(write_guard.deref_mut(), blknum)?;
+                    self.fill_buffer(write_guard.deref_mut(), blknum).await?;
                    write_guard.mark_valid();

                    // Swap for read lock
@@ -196,15 +210,9 @@ where
    }
 }

-impl BlockReader for FileBlockReader<File> {
+impl BlockReader for FileBlockReader {
    fn block_cursor(&self) -> BlockCursor<'_> {
-        BlockCursor::new(BlockReaderRef::FileBlockReaderFile(self))
-    }
-}
-
-impl BlockReader for FileBlockReader<VirtualFile> {
-    fn block_cursor(&self) -> BlockCursor<'_> {
-        BlockCursor::new(BlockReaderRef::FileBlockReaderVirtual(self))
+        BlockCursor::new(BlockReaderRef::FileBlockReader(self))
    }
 }

--- a/pageserver/src/tenant/disk_btree.rs
+++ b/pageserver/src/tenant/disk_btree.rs
@@ -26,7 +26,11 @@ use std::{cmp::Ordering, io, result};
 use thiserror::Error;
 use tracing::error;

-use crate::tenant::block_io::{BlockReader, BlockWriter};
+use crate::{
+    context::{DownloadBehavior, RequestContext},
+    task_mgr::TaskKind,
+    tenant::block_io::{BlockReader, BlockWriter},
+};

 // The maximum size of a value stored in the B-tree. 5 bytes is enough currently.
 pub const VALUE_SZ: usize = 5;
@@ -231,14 +235,19 @@ where
    ///
    /// Read the value for given key. Returns the value, or None if it doesn't exist.
    ///
-    pub async fn get(&self, search_key: &[u8; L]) -> Result<Option<u64>> {
+    pub async fn get(&self, search_key: &[u8; L], ctx: &RequestContext) -> Result<Option<u64>> {
        let mut result: Option<u64> = None;
-        self.visit(search_key, VisitDirection::Forwards, |key, value| {
-            if key == search_key {
-                result = Some(value);
-            }
-            false
-        })
+        self.visit(
+            search_key,
+            VisitDirection::Forwards,
+            |key, value| {
+                if key == search_key {
+                    result = Some(value);
+                }
+                false
+            },
+            ctx,
+        )
        .await?;
        Ok(result)
    }
@@ -253,6 +262,7 @@ where
        search_key: &[u8; L],
        dir: VisitDirection,
        mut visitor: V,
+        ctx: &RequestContext,
    ) -> Result<bool>
    where
        V: FnMut(&[u8], u64) -> bool,
@@ -262,7 +272,9 @@ where
        let block_cursor = self.reader.block_cursor();
        while let Some((node_blknum, opt_iter)) = stack.pop() {
            // Locate the node.
-            let node_buf = block_cursor.read_blk(self.start_blk + node_blknum).await?;
+            let node_buf = block_cursor
+                .read_blk(self.start_blk + node_blknum, ctx)
+                .await?;

            let node = OnDiskNode::deparse(node_buf.as_ref())?;
            let prefix_len = node.prefix_len as usize;
@@ -351,13 +363,14 @@ where
    #[allow(dead_code)]
    pub async fn dump(&self) -> Result<()> {
        let mut stack = Vec::new();
+        let ctx = RequestContext::new(TaskKind::DebugTool, DownloadBehavior::Error);

        stack.push((self.root_blk, String::new(), 0, 0, 0));

        let block_cursor = self.reader.block_cursor();

        while let Some((blknum, path, depth, child_idx, key_off)) = stack.pop() {
-            let blk = block_cursor.read_blk(self.start_blk + blknum).await?;
+            let blk = block_cursor.read_blk(self.start_blk + blknum, &ctx).await?;
            let buf: &[u8] = blk.as_ref();
            let node = OnDiskNode::<L>::deparse(buf)?;

@@ -688,6 +701,8 @@ impl<const L: usize> BuildNode<L> {
 #[cfg(test)]
 pub(crate) mod tests {
    use super::*;
+    use crate::context::DownloadBehavior;
+    use crate::task_mgr::TaskKind;
    use crate::tenant::block_io::{BlockCursor, BlockLease, BlockReaderRef};
    use rand::Rng;
    use std::collections::BTreeMap;
@@ -725,6 +740,8 @@ pub(crate) mod tests {
        let mut disk = TestDisk::new();
        let mut writer = DiskBtreeBuilder::<_, 6>::new(&mut disk);

+        let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);
+
        let all_keys: Vec<&[u8; 6]> = vec![
            b"xaaaaa", b"xaaaba", b"xaaaca", b"xabaaa", b"xababa", b"xabaca", b"xabada", b"xabadb",
        ];
@@ -745,12 +762,12 @@ pub(crate) mod tests {

        // Test the `get` function on all the keys.
        for (key, val) in all_data.iter() {
-            assert_eq!(reader.get(key).await?, Some(*val));
+            assert_eq!(reader.get(key, &ctx).await?, Some(*val));
        }
        // And on some keys that don't exist
-        assert_eq!(reader.get(b"aaaaaa").await?, None);
-        assert_eq!(reader.get(b"zzzzzz").await?, None);
-        assert_eq!(reader.get(b"xaaabx").await?, None);
+        assert_eq!(reader.get(b"aaaaaa", &ctx).await?, None);
+        assert_eq!(reader.get(b"zzzzzz", &ctx).await?, None);
+        assert_eq!(reader.get(b"xaaabx", &ctx).await?, None);

        // Test search with `visit` function
        let search_key = b"xabaaa";
@@ -762,10 +779,15 @@ pub(crate) mod tests {

        let mut data = Vec::new();
        reader
-            .visit(search_key, VisitDirection::Forwards, |key, value| {
-                data.push((key.to_vec(), value));
-                true
-            })
+            .visit(
+                search_key,
+                VisitDirection::Forwards,
+                |key, value| {
+                    data.push((key.to_vec(), value));
+                    true
+                },
+                &ctx,
+            )
            .await?;
        assert_eq!(data, expected);

@@ -778,18 +800,28 @@ pub(crate) mod tests {
        expected.reverse();
        let mut data = Vec::new();
        reader
-            .visit(search_key, VisitDirection::Backwards, |key, value| {
-                data.push((key.to_vec(), value));
-                true
-            })
+            .visit(
+                search_key,
+                VisitDirection::Backwards,
+                |key, value| {
+                    data.push((key.to_vec(), value));
+                    true
+                },
+                &ctx,
+            )
            .await?;
        assert_eq!(data, expected);

        // Backward scan where nothing matches
        reader
-            .visit(b"aaaaaa", VisitDirection::Backwards, |key, value| {
-                panic!("found unexpected key {}: {}", hex::encode(key), value);
-            })
+            .visit(
+                b"aaaaaa",
+                VisitDirection::Backwards,
+                |key, value| {
+                    panic!("found unexpected key {}: {}", hex::encode(key), value);
+                },
+                &ctx,
+            )
            .await?;

        // Full scan
@@ -799,10 +831,15 @@ pub(crate) mod tests {
            .collect();
        let mut data = Vec::new();
        reader
-            .visit(&[0u8; 6], VisitDirection::Forwards, |key, value| {
-                data.push((key.to_vec(), value));
-                true
-            })
+            .visit(
+                &[0u8; 6],
+                VisitDirection::Forwards,
+                |key, value| {
+                    data.push((key.to_vec(), value));
+                    true
+                },
+                &ctx,
+            )
            .await?;
        assert_eq!(data, expected);

@@ -813,6 +850,7 @@ pub(crate) mod tests {
    async fn lots_of_keys() -> Result<()> {
        let mut disk = TestDisk::new();
        let mut writer = DiskBtreeBuilder::<_, 8>::new(&mut disk);
+        let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);

        const NUM_KEYS: u64 = 1000;

@@ -851,14 +889,14 @@ pub(crate) mod tests {
        for search_key_int in 0..(NUM_KEYS * 2 + 10) {
            let search_key = u64::to_be_bytes(search_key_int);
            assert_eq!(
-                reader.get(&search_key).await?,
+                reader.get(&search_key, &ctx).await?,
                all_data.get(&search_key_int).cloned()
            );

            // Test a forward scan starting with this key
            result.lock().unwrap().clear();
            reader
-                .visit(&search_key, VisitDirection::Forwards, take_ten)
+                .visit(&search_key, VisitDirection::Forwards, take_ten, &ctx)
                .await?;
            let expected = all_data
                .range(search_key_int..)
@@ -870,7 +908,7 @@ pub(crate) mod tests {
            // And a backwards scan
            result.lock().unwrap().clear();
            reader
-                .visit(&search_key, VisitDirection::Backwards, take_ten)
+                .visit(&search_key, VisitDirection::Backwards, take_ten, &ctx)
                .await?;
            let expected = all_data
                .range(..=search_key_int)
@@ -886,7 +924,7 @@ pub(crate) mod tests {
        limit.store(usize::MAX, Ordering::Relaxed);
        result.lock().unwrap().clear();
        reader
-            .visit(&search_key, VisitDirection::Forwards, take_ten)
+            .visit(&search_key, VisitDirection::Forwards, take_ten, &ctx)
            .await?;
        let expected = all_data
            .iter()
@@ -899,7 +937,7 @@ pub(crate) mod tests {
        limit.store(usize::MAX, Ordering::Relaxed);
        result.lock().unwrap().clear();
        reader
-            .visit(&search_key, VisitDirection::Backwards, take_ten)
+            .visit(&search_key, VisitDirection::Backwards, take_ten, &ctx)
            .await?;
        let expected = all_data
            .iter()
@@ -913,6 +951,8 @@ pub(crate) mod tests {

    #[tokio::test]
    async fn random_data() -> Result<()> {
+        let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);
+
        // Generate random keys with exponential distribution, to
        // exercise the prefix compression
        const NUM_KEYS: usize = 100000;
@@ -939,22 +979,24 @@ pub(crate) mod tests {
        // Test get() operation on all the keys
        for (&key, &val) in all_data.iter() {
            let search_key = u128::to_be_bytes(key);
-            assert_eq!(reader.get(&search_key).await?, Some(val));
+            assert_eq!(reader.get(&search_key, &ctx).await?, Some(val));
        }

        // Test get() operations on random keys, most of which will not exist
        for _ in 0..100000 {
            let key_int = rand::thread_rng().gen::<u128>();
            let search_key = u128::to_be_bytes(key_int);
-            assert!(reader.get(&search_key).await? == all_data.get(&key_int).cloned());
+            assert!(reader.get(&search_key, &ctx).await? == all_data.get(&key_int).cloned());
        }

        // Test boundary cases
        assert!(
-            reader.get(&u128::to_be_bytes(u128::MIN)).await? == all_data.get(&u128::MIN).cloned()
+            reader.get(&u128::to_be_bytes(u128::MIN), &ctx).await?
+                == all_data.get(&u128::MIN).cloned()
        );
        assert!(
-            reader.get(&u128::to_be_bytes(u128::MAX)).await? == all_data.get(&u128::MAX).cloned()
+            reader.get(&u128::to_be_bytes(u128::MAX), &ctx).await?
+                == all_data.get(&u128::MAX).cloned()
        );

        Ok(())
@@ -985,6 +1027,7 @@ pub(crate) mod tests {
        // Build a tree from it
        let mut disk = TestDisk::new();
        let mut writer = DiskBtreeBuilder::<_, 26>::new(&mut disk);
+        let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);

        for (key, val) in disk_btree_test_data::TEST_DATA {
            writer.append(&key, val)?;
@@ -997,16 +1040,21 @@ pub(crate) mod tests {

        // Test get() operation on all the keys
        for (key, val) in disk_btree_test_data::TEST_DATA {
-            assert_eq!(reader.get(&key).await?, Some(val));
+            assert_eq!(reader.get(&key, &ctx).await?, Some(val));
        }

        // Test full scan
        let mut count = 0;
        reader
-            .visit(&[0u8; 26], VisitDirection::Forwards, |_key, _value| {
-                count += 1;
-                true
-            })
+            .visit(
+                &[0u8; 26],
+                VisitDirection::Forwards,
+                |_key, _value| {
+                    count += 1;
+                    true
+                },
+                &ctx,
+            )
            .await?;
        assert_eq!(count, disk_btree_test_data::TEST_DATA.len());

--- a/pageserver/src/tenant/ephemeral_file.rs
+++ b/pageserver/src/tenant/ephemeral_file.rs
@@ -2,6 +2,7 @@
 //! used to keep in-memory layers spilled on disk.

 use crate::config::PageServerConf;
+use crate::context::RequestContext;
 use crate::page_cache::{self, PAGE_SZ};
 use crate::tenant::block_io::{BlockCursor, BlockLease, BlockReader};
 use crate::virtual_file::VirtualFile;
@@ -9,7 +10,6 @@ use std::cmp::min;
 use std::fs::OpenOptions;
 use std::io::{self, ErrorKind};
 use std::ops::DerefMut;
-use std::os::unix::prelude::FileExt;
 use std::path::PathBuf;
 use std::sync::atomic::AtomicU64;
 use tracing::*;
@@ -29,7 +29,7 @@ pub struct EphemeralFile {
 }

 impl EphemeralFile {
-    pub fn create(
+    pub async fn create(
        conf: &PageServerConf,
        tenant_id: TenantId,
        timeline_id: TimelineId,
@@ -45,7 +45,8 @@ impl EphemeralFile {
        let file = VirtualFile::open_with_options(
            &filename,
            OpenOptions::new().read(true).write(true).create(true),
-        )?;
+        )
+        .await?;

        Ok(EphemeralFile {
            page_cache_file_id: page_cache::next_file_id(),
@@ -61,13 +62,17 @@ impl EphemeralFile {
        self.len
    }

-    pub(crate) async fn read_blk(&self, blknum: u32) -> Result<BlockLease, io::Error> {
+    pub(crate) async fn read_blk(
+        &self,
+        blknum: u32,
+        ctx: &RequestContext,
+    ) -> Result<BlockLease, io::Error> {
        let flushed_blknums = 0..self.len / PAGE_SZ as u64;
        if flushed_blknums.contains(&(blknum as u64)) {
            let cache = page_cache::get();
            loop {
                match cache
-                    .read_immutable_buf(self.page_cache_file_id, blknum)
+                    .read_immutable_buf(self.page_cache_file_id, blknum, ctx)
                    .await
                    .map_err(|e| {
                        std::io::Error::new(
@@ -88,7 +93,8 @@ impl EphemeralFile {
                        let buf: &mut [u8] = write_guard.deref_mut();
                        debug_assert_eq!(buf.len(), PAGE_SZ);
                        self.file
-                            .read_exact_at(&mut buf[..], blknum as u64 * PAGE_SZ as u64)?;
+                            .read_exact_at(&mut buf[..], blknum as u64 * PAGE_SZ as u64)
+                            .await?;
                        write_guard.mark_valid();

                        // Swap for read lock
@@ -102,7 +108,11 @@ impl EphemeralFile {
        }
    }

-    pub(crate) async fn write_blob(&mut self, srcbuf: &[u8]) -> Result<u64, io::Error> {
+    pub(crate) async fn write_blob(
+        &mut self,
+        srcbuf: &[u8],
+        ctx: &RequestContext,
+    ) -> Result<u64, io::Error> {
        struct Writer<'a> {
            ephemeral_file: &'a mut EphemeralFile,
            /// The block to which the next [`push_bytes`] will write.
@@ -119,7 +129,11 @@ impl EphemeralFile {
                })
            }
            #[inline(always)]
-            async fn push_bytes(&mut self, src: &[u8]) -> Result<(), io::Error> {
+            async fn push_bytes(
+                &mut self,
+                src: &[u8],
+                ctx: &RequestContext,
+            ) -> Result<(), io::Error> {
                let mut src_remaining = src;
                while !src_remaining.is_empty() {
                    let dst_remaining = &mut self.ephemeral_file.mutable_tail[self.off..];
@@ -128,10 +142,15 @@ impl EphemeralFile {
                    self.off += n;
                    src_remaining = &src_remaining[n..];
                    if self.off == PAGE_SZ {
-                        match self.ephemeral_file.file.write_all_at(
-                            &self.ephemeral_file.mutable_tail,
-                            self.blknum as u64 * PAGE_SZ as u64,
-                        ) {
+                        match self
+                            .ephemeral_file
+                            .file
+                            .write_all_at(
+                                &self.ephemeral_file.mutable_tail,
+                                self.blknum as u64 * PAGE_SZ as u64,
+                            )
+                            .await
+                        {
                            Ok(_) => {
                                // Pre-warm the page cache with what we just wrote.
                                // This isn't necessary for coherency/correctness, but it's how we've always done it.
@@ -140,6 +159,7 @@ impl EphemeralFile {
                                    .read_immutable_buf(
                                        self.ephemeral_file.page_cache_file_id,
                                        self.blknum,
+                                        ctx,
                                    )
                                    .await
                                {
@@ -193,15 +213,15 @@ impl EphemeralFile {
        if srcbuf.len() < 0x80 {
            // short one-byte length header
            let len_buf = [srcbuf.len() as u8];
-            writer.push_bytes(&len_buf).await?;
+            writer.push_bytes(&len_buf, ctx).await?;
        } else {
            let mut len_buf = u32::to_be_bytes(srcbuf.len() as u32);
            len_buf[0] |= 0x80;
-            writer.push_bytes(&len_buf).await?;
+            writer.push_bytes(&len_buf, ctx).await?;
        }

        // Write the payload
-        writer.push_bytes(srcbuf).await?;
+        writer.push_bytes(srcbuf, ctx).await?;

        if srcbuf.len() < 0x80 {
            self.len += 1;
@@ -255,6 +275,8 @@ impl BlockReader for EphemeralFile {
 #[cfg(test)]
 mod tests {
    use super::*;
+    use crate::context::DownloadBehavior;
+    use crate::task_mgr::TaskKind;
    use crate::tenant::block_io::{BlockCursor, BlockReaderRef};
    use rand::{thread_rng, RngCore};
    use std::fs;
@@ -262,7 +284,15 @@ mod tests {

    fn harness(
        test_name: &str,
-    ) -> Result<(&'static PageServerConf, TenantId, TimelineId), io::Error> {
+    ) -> Result<
+        (
+            &'static PageServerConf,
+            TenantId,
+            TimelineId,
+            RequestContext,
+        ),
+        io::Error,
+    > {
        let repo_dir = PageServerConf::test_repo_dir(test_name);
        let _ = fs::remove_dir_all(&repo_dir);
        let conf = PageServerConf::dummy_conf(repo_dir);
@@ -274,46 +304,57 @@ mod tests {
        let timeline_id = TimelineId::from_str("22000000000000000000000000000000").unwrap();
        fs::create_dir_all(conf.timeline_path(&tenant_id, &timeline_id))?;

-        Ok((conf, tenant_id, timeline_id))
+        let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);
+
+        Ok((conf, tenant_id, timeline_id, ctx))
    }

    #[tokio::test]
    async fn test_ephemeral_blobs() -> Result<(), io::Error> {
-        let (conf, tenant_id, timeline_id) = harness("ephemeral_blobs")?;
+        let (conf, tenant_id, timeline_id, ctx) = harness("ephemeral_blobs")?;

-        let mut file = EphemeralFile::create(conf, tenant_id, timeline_id)?;
+        let mut file = EphemeralFile::create(conf, tenant_id, timeline_id).await?;

-        let pos_foo = file.write_blob(b"foo").await?;
+        let pos_foo = file.write_blob(b"foo", &ctx).await?;
        assert_eq!(
            b"foo",
-            file.block_cursor().read_blob(pos_foo).await?.as_slice()
+            file.block_cursor()
+                .read_blob(pos_foo, &ctx)
+                .await?
+                .as_slice()
        );
-        let pos_bar = file.write_blob(b"bar").await?;
+        let pos_bar = file.write_blob(b"bar", &ctx).await?;
        assert_eq!(
            b"foo",
-            file.block_cursor().read_blob(pos_foo).await?.as_slice()
+            file.block_cursor()
+                .read_blob(pos_foo, &ctx)
+                .await?
+                .as_slice()
        );
        assert_eq!(
            b"bar",
-            file.block_cursor().read_blob(pos_bar).await?.as_slice()
+            file.block_cursor()
+                .read_blob(pos_bar, &ctx)
+                .await?
+                .as_slice()
        );

        let mut blobs = Vec::new();
        for i in 0..10000 {
            let data = Vec::from(format!("blob{}", i).as_bytes());
-            let pos = file.write_blob(&data).await?;
+            let pos = file.write_blob(&data, &ctx).await?;
            blobs.push((pos, data));
        }
        // also test with a large blobs
        for i in 0..100 {
            let data = format!("blob{}", i).as_bytes().repeat(100);
-            let pos = file.write_blob(&data).await?;
+            let pos = file.write_blob(&data, &ctx).await?;
            blobs.push((pos, data));
        }

        let cursor = BlockCursor::new(BlockReaderRef::EphemeralFile(&file));
        for (pos, expected) in blobs {
-            let actual = cursor.read_blob(pos).await?;
+            let actual = cursor.read_blob(pos, &ctx).await?;
            assert_eq!(actual, expected);
        }

@@ -321,8 +362,8 @@ mod tests {
        let mut large_data = Vec::new();
        large_data.resize(20000, 0);
        thread_rng().fill_bytes(&mut large_data);
-        let pos_large = file.write_blob(&large_data).await?;
-        let result = file.block_cursor().read_blob(pos_large).await?;
+        let pos_large = file.write_blob(&large_data, &ctx).await?;
+        let result = file.block_cursor().read_blob(pos_large, &ctx).await?;
        assert_eq!(result, large_data);

        Ok(())
--- a/pageserver/src/tenant/manifest.rs
+++ b/pageserver/src/tenant/manifest.rs
@@ -1,325 +0,0 @@
-//! This module contains the encoding and decoding of the local manifest file.
-//!
-//! MANIFEST is a write-ahead log which is stored locally to each timeline. It
-//! records the state of the storage engine. It contains a snapshot of the
-//! state and all operations proceeding that snapshot. The file begins with a
-//! header recording MANIFEST version number. After that, it contains a snapshot.
-//! The snapshot is followed by a list of operations. Each operation is a list
-//! of records. Each record is either an addition or a removal of a layer.
-//!
-//! With MANIFEST, we can:
-//!
-//! 1. recover state quickly by reading the file, potentially boosting the
-//!    startup speed.
-//! 2. ensure all operations are atomic and avoid corruption, solving issues
-//!    like redundant image layer and preparing us for future compaction
-//!    strategies.
-//!
-//! There is also a format for storing all layer files on S3, called
-//! `index_part.json`. Compared with index_part, MANIFEST is an WAL which
-//! records all operations as logs, and therefore we can easily replay the
-//! operations when recovering from crash, while ensuring those operations
-//! are atomic upon restart.
-//!
-//! Currently, this is not used in the system. Future refactors will ensure
-//! the storage state will be recorded in this file, and the system can be
-//! recovered from this file. This is tracked in
-//! <https://github.com/neondatabase/neon/issues/4418>
-
-use std::io::{self, Read, Write};
-
-use crate::virtual_file::VirtualFile;
-use anyhow::Result;
-use bytes::{Buf, BufMut, Bytes, BytesMut};
-use crc32c::crc32c;
-use serde::{Deserialize, Serialize};
-use tracing::log::warn;
-use utils::lsn::Lsn;
-
-use super::storage_layer::PersistentLayerDesc;
-
-pub struct Manifest {
-    file: VirtualFile,
-}
-
-#[derive(Clone, Serialize, Deserialize, PartialEq, Eq, Debug)]
-pub struct Snapshot {
-    pub layers: Vec<PersistentLayerDesc>,
-}
-
-/// serde by default encode this in tagged enum, and therefore it will be something
-/// like `{ "AddLayer": { ... } }`.
-#[derive(Clone, Serialize, Deserialize, PartialEq, Eq, Debug)]
-pub enum Record {
-    AddLayer(PersistentLayerDesc),
-    RemoveLayer(PersistentLayerDesc),
-}
-
-/// `echo neon.manifest | sha1sum` and take the leading 8 bytes.
-const MANIFEST_MAGIC_NUMBER: u64 = 0xf5c44592b806109c;
-const MANIFEST_VERSION: u64 = 1;
-
-#[derive(Clone, Serialize, Deserialize, PartialEq, Eq, Debug)]
-pub struct ManifestHeader {
-    magic_number: u64,
-    version: u64,
-}
-
-const MANIFEST_HEADER_LEN: usize = 16;
-
-impl ManifestHeader {
-    fn encode(&self) -> BytesMut {
-        let mut buf = BytesMut::with_capacity(MANIFEST_HEADER_LEN);
-        buf.put_u64(self.magic_number);
-        buf.put_u64(self.version);
-        buf
-    }
-
-    fn decode(mut buf: &[u8]) -> Self {
-        assert!(buf.len() == MANIFEST_HEADER_LEN, "invalid header");
-        Self {
-            magic_number: buf.get_u64(),
-            version: buf.get_u64(),
-        }
-    }
-}
-
-#[derive(Clone, Serialize, Deserialize, PartialEq, Eq, Debug)]
-pub enum Operation {
-    /// A snapshot of the current state.
-    ///
-    /// Lsn field represents the LSN that is persisted to disk for this snapshot.
-    Snapshot(Snapshot, Lsn),
-    /// An atomic operation that changes the state.
-    ///
-    /// Lsn field represents the LSN that is persisted to disk after the operation is done.
-    /// This will only change when new L0 is flushed to the disk.
-    Operation(Vec<Record>, Lsn),
-}
-
-struct RecordHeader {
-    size: u32,
-    checksum: u32,
-}
-
-const RECORD_HEADER_LEN: usize = 8;
-
-impl RecordHeader {
-    fn encode(&self) -> BytesMut {
-        let mut buf = BytesMut::with_capacity(RECORD_HEADER_LEN);
-        buf.put_u32(self.size);
-        buf.put_u32(self.checksum);
-        buf
-    }
-
-    fn decode(mut buf: &[u8]) -> Self {
-        assert!(buf.len() == RECORD_HEADER_LEN, "invalid header");
-        Self {
-            size: buf.get_u32(),
-            checksum: buf.get_u32(),
-        }
-    }
-}
-
-#[derive(Debug, thiserror::Error)]
-pub enum ManifestLoadError {
-    #[error("manifest header is corrupted")]
-    CorruptedManifestHeader,
-    #[error("unsupported manifest version: got {0}, expected {1}")]
-    UnsupportedVersion(u64, u64),
-    #[error("error when decoding record: {0}")]
-    DecodeRecord(serde_json::Error),
-    #[error("I/O error: {0}")]
-    Io(io::Error),
-}
-
-#[must_use = "Should check if the manifest is partially corrupted"]
-pub struct ManifestPartiallyCorrupted(bool);
-
-impl Manifest {
-    /// Create a new manifest by writing the manifest header and a snapshot record to the given file.
-    pub fn init(file: VirtualFile, snapshot: Snapshot, lsn: Lsn) -> Result<Self> {
-        let mut manifest = Self { file };
-        manifest.append_manifest_header(ManifestHeader {
-            magic_number: MANIFEST_MAGIC_NUMBER,
-            version: MANIFEST_VERSION,
-        })?;
-        manifest.append_operation(Operation::Snapshot(snapshot, lsn))?;
-        Ok(manifest)
-    }
-
-    /// Load a manifest. Returns the manifest and a list of operations. If the manifest is corrupted,
-    /// the bool flag will be set to true and the user is responsible to reconstruct a new manifest and
-    /// backup the current one.
-    pub fn load(
-        mut file: VirtualFile,
-    ) -> Result<(Self, Vec<Operation>, ManifestPartiallyCorrupted), ManifestLoadError> {
-        let mut buf = vec![];
-        file.read_to_end(&mut buf).map_err(ManifestLoadError::Io)?;
-
-        // Read manifest header
-        let mut buf = Bytes::from(buf);
-        if buf.remaining() < MANIFEST_HEADER_LEN {
-            return Err(ManifestLoadError::CorruptedManifestHeader);
-        }
-        let header = ManifestHeader::decode(&buf[..MANIFEST_HEADER_LEN]);
-        buf.advance(MANIFEST_HEADER_LEN);
-        if header.version != MANIFEST_VERSION {
-            return Err(ManifestLoadError::UnsupportedVersion(
-                header.version,
-                MANIFEST_VERSION,
-            ));
-        }
-
-        // Read operations
-        let mut operations = Vec::new();
-        let corrupted = loop {
-            if buf.remaining() == 0 {
-                break false;
-            }
-            if buf.remaining() < RECORD_HEADER_LEN {
-                warn!("incomplete header when decoding manifest, could be corrupted");
-                break true;
-            }
-            let RecordHeader { size, checksum } = RecordHeader::decode(&buf[..RECORD_HEADER_LEN]);
-            let size = size as usize;
-            buf.advance(RECORD_HEADER_LEN);
-            if buf.remaining() < size {
-                warn!("incomplete data when decoding manifest, could be corrupted");
-                break true;
-            }
-            let data = &buf[..size];
-            if crc32c(data) != checksum {
-                warn!("checksum mismatch when decoding manifest, could be corrupted");
-                break true;
-            }
-            // if the following decode fails, we cannot use the manifest or safely ignore any record.
-            operations.push(serde_json::from_slice(data).map_err(ManifestLoadError::DecodeRecord)?);
-            buf.advance(size);
-        };
-        Ok((
-            Self { file },
-            operations,
-            ManifestPartiallyCorrupted(corrupted),
-        ))
-    }
-
-    fn append_data(&mut self, data: &[u8]) -> Result<()> {
-        if data.len() >= u32::MAX as usize {
-            panic!("data too large");
-        }
-        let header = RecordHeader {
-            size: data.len() as u32,
-            checksum: crc32c(data),
-        };
-        let header = header.encode();
-        self.file.write_all(&header)?;
-        self.file.write_all(data)?;
-        self.file.sync_all()?;
-        Ok(())
-    }
-
-    fn append_manifest_header(&mut self, header: ManifestHeader) -> Result<()> {
-        let encoded = header.encode();
-        self.file.write_all(&encoded)?;
-        Ok(())
-    }
-
-    /// Add an operation to the manifest. The operation will be appended to the end of the file,
-    /// and the file will fsync.
-    pub fn append_operation(&mut self, operation: Operation) -> Result<()> {
-        let encoded = Vec::from(serde_json::to_string(&operation)?);
-        self.append_data(&encoded)
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use std::fs::OpenOptions;
-
-    use crate::repository::Key;
-
-    use super::*;
-
-    #[test]
-    fn test_read_manifest() {
-        let testdir = crate::config::PageServerConf::test_repo_dir("test_read_manifest");
-        std::fs::create_dir_all(&testdir).unwrap();
-        let file = VirtualFile::create(&testdir.join("MANIFEST")).unwrap();
-        let layer1 = PersistentLayerDesc::new_test(Key::from_i128(0)..Key::from_i128(233));
-        let layer2 = PersistentLayerDesc::new_test(Key::from_i128(233)..Key::from_i128(2333));
-        let layer3 = PersistentLayerDesc::new_test(Key::from_i128(2333)..Key::from_i128(23333));
-        let layer4 = PersistentLayerDesc::new_test(Key::from_i128(23333)..Key::from_i128(233333));
-
-        // Write a manifest with a snapshot and some operations
-        let snapshot = Snapshot {
-            layers: vec![layer1, layer2],
-        };
-        let mut manifest = Manifest::init(file, snapshot.clone(), Lsn::from(0)).unwrap();
-        manifest
-            .append_operation(Operation::Operation(
-                vec![Record::AddLayer(layer3.clone())],
-                Lsn::from(1),
-            ))
-            .unwrap();
-        drop(manifest);
-
-        // Open the second time and write
-        let file = VirtualFile::open_with_options(
-            &testdir.join("MANIFEST"),
-            OpenOptions::new()
-                .read(true)
-                .write(true)
-                .create_new(false)
-                .truncate(false),
-        )
-        .unwrap();
-        let (mut manifest, operations, corrupted) = Manifest::load(file).unwrap();
-        assert!(!corrupted.0);
-        assert_eq!(operations.len(), 2);
-        assert_eq!(
-            &operations[0],
-            &Operation::Snapshot(snapshot.clone(), Lsn::from(0))
-        );
-        assert_eq!(
-            &operations[1],
-            &Operation::Operation(vec![Record::AddLayer(layer3.clone())], Lsn::from(1))
-        );
-        manifest
-            .append_operation(Operation::Operation(
-                vec![
-                    Record::RemoveLayer(layer3.clone()),
-                    Record::AddLayer(layer4.clone()),
-                ],
-                Lsn::from(2),
-            ))
-            .unwrap();
-        drop(manifest);
-
-        // Open the third time and verify
-        let file = VirtualFile::open_with_options(
-            &testdir.join("MANIFEST"),
-            OpenOptions::new()
-                .read(true)
-                .write(true)
-                .create_new(false)
-                .truncate(false),
-        )
-        .unwrap();
-        let (_manifest, operations, corrupted) = Manifest::load(file).unwrap();
-        assert!(!corrupted.0);
-        assert_eq!(operations.len(), 3);
-        assert_eq!(&operations[0], &Operation::Snapshot(snapshot, Lsn::from(0)));
-        assert_eq!(
-            &operations[1],
-            &Operation::Operation(vec![Record::AddLayer(layer3.clone())], Lsn::from(1))
-        );
-        assert_eq!(
-            &operations[2],
-            &Operation::Operation(
-                vec![Record::RemoveLayer(layer3), Record::AddLayer(layer4)],
-                Lsn::from(2)
-            )
-        );
-    }
-}
--- a/pageserver/src/tenant/metadata.rs
+++ b/pageserver/src/tenant/metadata.rs
@@ -8,14 +8,13 @@
 //!
 //! [`remote_timeline_client`]: super::remote_timeline_client

-use std::fs::{File, OpenOptions};
-use std::io::{self, Write};
+use std::io::{self};

-use anyhow::{bail, ensure, Context};
+use anyhow::{ensure, Context};
 use serde::{de::Error, Deserialize, Serialize, Serializer};
 use thiserror::Error;
-use tracing::info_span;
 use utils::bin_ser::SerializeError;
+use utils::crashsafe::path_with_suffix_extension;
 use utils::{
    bin_ser::BeSer,
    id::{TenantId, TimelineId},
@@ -24,6 +23,7 @@ use utils::{

 use crate::config::PageServerConf;
 use crate::virtual_file::VirtualFile;
+use crate::TEMP_FILE_SUFFIX;

 /// Use special format number to enable backward compatibility.
 const METADATA_FORMAT_VERSION: u16 = 4;
@@ -230,6 +230,23 @@ impl TimelineMetadata {
    pub fn pg_version(&self) -> u32 {
        self.body.pg_version
    }
+
+    // Checksums make it awkward to build a valid instance by hand.  This helper
+    // provides a TimelineMetadata with a valid checksum in its header.
+    #[cfg(test)]
+    pub fn example() -> Self {
+        let instance = Self::new(
+            "0/16960E8".parse::<Lsn>().unwrap(),
+            None,
+            None,
+            Lsn::from_hex("00000000").unwrap(),
+            Lsn::from_hex("00000000").unwrap(),
+            Lsn::from_hex("00000000").unwrap(),
+            0,
+        );
+        let bytes = instance.to_bytes().unwrap();
+        Self::from_bytes(&bytes).unwrap()
+    }
 }

 impl<'de> Deserialize<'de> for TimelineMetadata {
@@ -255,38 +272,19 @@ impl Serialize for TimelineMetadata {
 }

 /// Save timeline metadata to file
-pub fn save_metadata(
+#[tracing::instrument(skip_all, fields(%tenant_id, %timeline_id))]
+pub async fn save_metadata(
    conf: &'static PageServerConf,
    tenant_id: &TenantId,
    timeline_id: &TimelineId,
    data: &TimelineMetadata,
-    first_save: bool,
 ) -> anyhow::Result<()> {
-    let _enter = info_span!("saving metadata").entered();
    let path = conf.metadata_path(tenant_id, timeline_id);
-    // use OpenOptions to ensure file presence is consistent with first_save
-    let mut file = VirtualFile::open_with_options(
-        &path,
-        OpenOptions::new().write(true).create_new(first_save),
-    )
-    .context("open_with_options")?;
-
-    let metadata_bytes = data.to_bytes().context("Failed to get metadata bytes")?;
-
-    if file.write(&metadata_bytes)? != metadata_bytes.len() {
-        bail!("Could not write all the metadata bytes in a single call");
-    }
-    file.sync_all()?;
-
-    // fsync the parent directory to ensure the directory entry is durable
-    if first_save {
-        let timeline_dir = File::open(
-            path.parent()
-                .expect("Metadata should always have a parent dir"),
-        )?;
-        timeline_dir.sync_all()?;
-    }
-
+    let temp_path = path_with_suffix_extension(&path, TEMP_FILE_SUFFIX);
+    let metadata_bytes = data.to_bytes().context("serialize metadata")?;
+    VirtualFile::crashsafe_overwrite(&path, &temp_path, &metadata_bytes)
+        .await
+        .context("write metadata")?;
    Ok(())
 }

--- a/pageserver/src/tenant/mgr.rs
+++ b/pageserver/src/tenant/mgr.rs
@@ -1,9 +1,10 @@
 //! This module acts as a switchboard to access different repositories managed by this
 //! page server.

+use rand::{distributions::Alphanumeric, Rng};
 use std::collections::{hash_map, HashMap};
 use std::ffi::OsStr;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use tokio::fs;

@@ -11,6 +12,7 @@ use anyhow::Context;
 use once_cell::sync::Lazy;
 use tokio::sync::RwLock;
 use tokio::task::JoinSet;
+use tokio_util::sync::CancellationToken;
 use tracing::*;

 use remote_storage::GenericRemoteStorage;
@@ -18,13 +20,16 @@ use utils::crashsafe;

 use crate::config::PageServerConf;
 use crate::context::{DownloadBehavior, RequestContext};
+use crate::control_plane_client::ControlPlaneClient;
 use crate::task_mgr::{self, TaskKind};
 use crate::tenant::config::TenantConfOpt;
 use crate::tenant::delete::DeleteTenantFlow;
 use crate::tenant::{create_tenant_files, CreateTenantFilesMode, Tenant, TenantState};
-use crate::{InitializationOrder, IGNORED_TENANT_FILE_NAME};
+use crate::{InitializationOrder, IGNORED_TENANT_FILE_NAME, TEMP_FILE_SUFFIX};

+use utils::crashsafe::path_with_suffix_extension;
 use utils::fs_ext::PathExt;
+use utils::generation::Generation;
 use utils::id::{TenantId, TimelineId};

 use super::delete::DeleteTenantError;
@@ -59,6 +64,39 @@ impl TenantsMap {
    }
 }

+/// This is "safe" in that that it won't leave behind a partially deleted directory
+/// at the original path, because we rename with TEMP_FILE_SUFFIX before starting deleting
+/// the contents.
+///
+/// This is pageserver-specific, as it relies on future processes after a crash to check
+/// for TEMP_FILE_SUFFIX when loading things.
+async fn safe_remove_tenant_dir_all(path: impl AsRef<Path>) -> std::io::Result<()> {
+    let tmp_path = safe_rename_tenant_dir(path).await?;
+    fs::remove_dir_all(tmp_path).await
+}
+
+async fn safe_rename_tenant_dir(path: impl AsRef<Path>) -> std::io::Result<PathBuf> {
+    let parent = path
+        .as_ref()
+        .parent()
+        // It is invalid to call this function with a relative path.  Tenant directories
+        // should always have a parent.
+        .ok_or(std::io::Error::new(
+            std::io::ErrorKind::InvalidInput,
+            "Path must be absolute",
+        ))?;
+    let rand_suffix = rand::thread_rng()
+        .sample_iter(&Alphanumeric)
+        .take(8)
+        .map(char::from)
+        .collect::<String>()
+        + TEMP_FILE_SUFFIX;
+    let tmp_path = path_with_suffix_extension(&path, &rand_suffix);
+    fs::rename(&path, &tmp_path).await?;
+    fs::File::open(parent).await?.sync_all().await?;
+    Ok(tmp_path)
+}
+
 static TENANTS: Lazy<RwLock<TenantsMap>> = Lazy::new(|| RwLock::new(TenantsMap::Initializing));

 /// Initialize repositories with locally available timelines.
@@ -69,12 +107,21 @@ pub async fn init_tenant_mgr(
    conf: &'static PageServerConf,
    resources: TenantSharedResources,
    init_order: InitializationOrder,
+    cancel: CancellationToken,
 ) -> anyhow::Result<()> {
    // Scan local filesystem for attached tenants
    let tenants_dir = conf.tenants_path();

    let mut tenants = HashMap::new();

+    // If we are configured to use the control plane API, then it is the source of truth for what tenants to load.
+    let tenant_generations = if let Some(client) = ControlPlaneClient::new(conf, &cancel) {
+        Some(client.re_attach().await?)
+    } else {
+        info!("Control plane API not configured, tenant generations are disabled");
+        None
+    };
+
    let mut dir_entries = fs::read_dir(&tenants_dir)
        .await
        .with_context(|| format!("Failed to list tenants dir {tenants_dir:?}"))?;
@@ -91,6 +138,8 @@ pub async fn init_tenant_mgr(
                        "Found temporary tenant directory, removing: {}",
                        tenant_dir_path.display()
                    );
+                    // No need to use safe_remove_tenant_dir_all because this is already
+                    // a temporary path
                    if let Err(e) = fs::remove_dir_all(&tenant_dir_path).await {
                        error!(
                            "Failed to remove temporary directory '{}': {:?}",
@@ -122,9 +171,53 @@ pub async fn init_tenant_mgr(
                        continue;
                    }

+                    let tenant_id = match tenant_dir_path
+                        .file_name()
+                        .and_then(OsStr::to_str)
+                        .unwrap_or_default()
+                        .parse::<TenantId>()
+                    {
+                        Ok(id) => id,
+                        Err(_) => {
+                            warn!(
+                                "Invalid tenant path (garbage in our repo directory?): {}",
+                                tenant_dir_path.display()
+                            );
+                            continue;
+                        }
+                    };
+
+                    let generation = if let Some(generations) = &tenant_generations {
+                        // We have a generation map: treat it as the authority for whether
+                        // this tenant is really attached.
+                        if let Some(gen) = generations.get(&tenant_id) {
+                            *gen
+                        } else {
+                            info!("Detaching tenant {tenant_id}, control plane omitted it in re-attach response");
+                            if let Err(e) = safe_remove_tenant_dir_all(&tenant_dir_path).await {
+                                error!(
+                                    "Failed to remove detached tenant directory '{}': {:?}",
+                                    tenant_dir_path.display(),
+                                    e
+                                );
+                            }
+                            continue;
+                        }
+                    } else {
+                        // Legacy mode: no generation information, any tenant present
+                        // on local disk may activate
+                        info!(
+                            "Starting tenant {} in legacy mode, no generation",
+                            tenant_dir_path.display()
+                        );
+                        Generation::none()
+                    };
+
                    match schedule_local_tenant_processing(
                        conf,
+                        tenant_id,
                        &tenant_dir_path,
+                        generation,
                        resources.clone(),
                        Some(init_order.clone()),
                        &TENANTS,
@@ -158,9 +251,12 @@ pub async fn init_tenant_mgr(
    Ok(())
 }

+#[allow(clippy::too_many_arguments)]
 pub(crate) fn schedule_local_tenant_processing(
    conf: &'static PageServerConf,
+    tenant_id: TenantId,
    tenant_path: &Path,
+    generation: Generation,
    resources: TenantSharedResources,
    init_order: Option<InitializationOrder>,
    tenants: &'static tokio::sync::RwLock<TenantsMap>,
@@ -181,15 +277,6 @@ pub(crate) fn schedule_local_tenant_processing(
        "Cannot load tenant from empty directory {tenant_path:?}"
    );

-    let tenant_id = tenant_path
-        .file_name()
-        .and_then(OsStr::to_str)
-        .unwrap_or_default()
-        .parse::<TenantId>()
-        .with_context(|| {
-            format!("Could not parse tenant id out of the tenant dir name in path {tenant_path:?}")
-        })?;
-
    let tenant_ignore_mark = conf.tenant_ignore_mark_file_path(&tenant_id);
    anyhow::ensure!(
        !conf.tenant_ignore_mark_file_path(&tenant_id).exists(),
@@ -202,6 +289,7 @@ pub(crate) fn schedule_local_tenant_processing(
            match Tenant::spawn_attach(
                conf,
                tenant_id,
+                generation,
                resources.broker_client,
                tenants,
                remote_storage,
@@ -224,7 +312,9 @@ pub(crate) fn schedule_local_tenant_processing(
    } else {
        info!("tenant {tenant_id} is assumed to be loadable, starting load operation");
        // Start loading the tenant into memory. It will initially be in Loading state.
-        Tenant::spawn_load(conf, tenant_id, resources, init_order, tenants, ctx)
+        Tenant::spawn_load(
+            conf, tenant_id, generation, resources, init_order, tenants, ctx,
+        )
    };
    Ok(tenant)
 }
@@ -347,15 +437,16 @@ pub async fn create_tenant(
    conf: &'static PageServerConf,
    tenant_conf: TenantConfOpt,
    tenant_id: TenantId,
+    generation: Generation,
    broker_client: storage_broker::BrokerClientChannel,
    remote_storage: Option<GenericRemoteStorage>,
    ctx: &RequestContext,
 ) -> Result<Arc<Tenant>, TenantMapInsertError> {
-    tenant_map_insert(tenant_id, || {
+    tenant_map_insert(tenant_id, || async {
        // We're holding the tenants lock in write mode while doing local IO.
        // If this section ever becomes contentious, introduce a new `TenantState::Creating`
        // and do the work in that state.
-        let tenant_directory = super::create_tenant_files(conf, tenant_conf, &tenant_id, CreateTenantFilesMode::Create)?;
+        let tenant_directory = super::create_tenant_files(conf, tenant_conf, &tenant_id, CreateTenantFilesMode::Create).await?;
        // TODO: tenant directory remains on disk if we bail out from here on.
        //       See https://github.com/neondatabase/neon/issues/4233

@@ -364,7 +455,8 @@ pub async fn create_tenant(
            remote_storage,
        };
        let created_tenant =
-            schedule_local_tenant_processing(conf, &tenant_directory, tenant_resources, None, &TENANTS, ctx)?;
+            schedule_local_tenant_processing(conf, tenant_id, &tenant_directory,
+                generation, tenant_resources, None, &TENANTS, ctx)?;
        // TODO: tenant object & its background loops remain, untracked in tenant map, if we fail here.
        //      See https://github.com/neondatabase/neon/issues/4233

@@ -394,7 +486,8 @@ pub async fn set_new_tenant_config(
    let tenant = get_tenant(tenant_id, true).await?;

    let tenant_config_path = conf.tenant_config_path(&tenant_id);
-    Tenant::persist_tenant_config(&tenant_id, &tenant_config_path, new_tenant_conf, false)
+    Tenant::persist_tenant_config(&tenant_id, &tenant_config_path, new_tenant_conf)
+        .await
        .map_err(SetNewTenantConfigError::Persist)?;
    tenant.set_new_tenant_config(new_tenant_conf);
    Ok(())
@@ -410,6 +503,8 @@ pub enum GetTenantError {

 /// Gets the tenant from the in-memory data, erroring if it's absent or is not fitting to the query.
 /// `active_only = true` allows to query only tenants that are ready for operations, erroring on other kinds of tenants.
+///
+/// This method is cancel-safe.
 pub async fn get_tenant(
    tenant_id: TenantId,
    active_only: bool,
@@ -469,7 +564,24 @@ pub async fn detach_tenant(
    tenant_id: TenantId,
    detach_ignored: bool,
 ) -> Result<(), TenantStateError> {
-    detach_tenant0(conf, &TENANTS, tenant_id, detach_ignored).await
+    let tmp_path = detach_tenant0(conf, &TENANTS, tenant_id, detach_ignored).await?;
+    // Although we are cleaning up the tenant, this task is not meant to be bound by the lifetime of the tenant in memory.
+    // After a tenant is detached, there are no more task_mgr tasks for that tenant_id.
+    let task_tenant_id = None;
+    task_mgr::spawn(
+        task_mgr::BACKGROUND_RUNTIME.handle(),
+        TaskKind::MgmtRequest,
+        task_tenant_id,
+        None,
+        "tenant_files_delete",
+        false,
+        async move {
+            fs::remove_dir_all(tmp_path.as_path())
+                .await
+                .with_context(|| format!("tenant directory {:?} deletion", tmp_path))
+        },
+    );
+    Ok(())
 }

 async fn detach_tenant0(
@@ -477,20 +589,16 @@ async fn detach_tenant0(
    tenants: &tokio::sync::RwLock<TenantsMap>,
    tenant_id: TenantId,
    detach_ignored: bool,
-) -> Result<(), TenantStateError> {
-    let local_files_cleanup_operation = |tenant_id_to_clean| async move {
+) -> Result<PathBuf, TenantStateError> {
+    let tenant_dir_rename_operation = |tenant_id_to_clean| async move {
        let local_tenant_directory = conf.tenant_path(&tenant_id_to_clean);
-        fs::remove_dir_all(&local_tenant_directory)
+        safe_rename_tenant_dir(&local_tenant_directory)
            .await
-            .with_context(|| {
-                format!("local tenant directory {local_tenant_directory:?} removal")
-            })?;
-        Ok(())
+            .with_context(|| format!("local tenant directory {local_tenant_directory:?} rename"))
    };

    let removal_result =
-        remove_tenant_from_memory(tenants, tenant_id, local_files_cleanup_operation(tenant_id))
-            .await;
+        remove_tenant_from_memory(tenants, tenant_id, tenant_dir_rename_operation(tenant_id)).await;

    // Ignored tenants are not present in memory and will bail the removal from memory operation.
    // Before returning the error, check for ignored tenant removal case — we only need to clean its local files then.
@@ -498,10 +606,10 @@ async fn detach_tenant0(
        let tenant_ignore_mark = conf.tenant_ignore_mark_file_path(&tenant_id);
        if tenant_ignore_mark.exists() {
            info!("Detaching an ignored tenant");
-            local_files_cleanup_operation(tenant_id)
+            let tmp_path = tenant_dir_rename_operation(tenant_id)
                .await
-                .with_context(|| format!("Ignored tenant {tenant_id} local files cleanup"))?;
-            return Ok(());
+                .with_context(|| format!("Ignored tenant {tenant_id} local directory rename"))?;
+            return Ok(tmp_path);
        }
    }

@@ -511,11 +619,12 @@ async fn detach_tenant0(
 pub async fn load_tenant(
    conf: &'static PageServerConf,
    tenant_id: TenantId,
+    generation: Generation,
    broker_client: storage_broker::BrokerClientChannel,
    remote_storage: Option<GenericRemoteStorage>,
    ctx: &RequestContext,
 ) -> Result<(), TenantMapInsertError> {
-    tenant_map_insert(tenant_id, || {
+    tenant_map_insert(tenant_id, || async {
        let tenant_path = conf.tenant_path(&tenant_id);
        let tenant_ignore_mark = conf.tenant_ignore_mark_file_path(&tenant_id);
        if tenant_ignore_mark.exists() {
@@ -527,7 +636,7 @@ pub async fn load_tenant(
            broker_client,
            remote_storage,
        };
-        let new_tenant = schedule_local_tenant_processing(conf, &tenant_path,  resources, None,  &TENANTS, ctx)
+        let new_tenant = schedule_local_tenant_processing(conf, tenant_id, &tenant_path, generation, resources, None,  &TENANTS, ctx)
            .with_context(|| {
                format!("Failed to schedule tenant processing in path {tenant_path:?}")
            })?;
@@ -591,13 +700,14 @@ pub async fn list_tenants() -> Result<Vec<(TenantId, TenantState)>, TenantMapLis
 pub async fn attach_tenant(
    conf: &'static PageServerConf,
    tenant_id: TenantId,
+    generation: Generation,
    tenant_conf: TenantConfOpt,
    broker_client: storage_broker::BrokerClientChannel,
    remote_storage: GenericRemoteStorage,
    ctx: &RequestContext,
 ) -> Result<(), TenantMapInsertError> {
-    tenant_map_insert(tenant_id, || {
-        let tenant_dir = create_tenant_files(conf, tenant_conf, &tenant_id, CreateTenantFilesMode::Attach)?;
+    tenant_map_insert(tenant_id, || async {
+        let tenant_dir = create_tenant_files(conf, tenant_conf, &tenant_id, CreateTenantFilesMode::Attach).await?;
        // TODO: tenant directory remains on disk if we bail out from here on.
        //       See https://github.com/neondatabase/neon/issues/4233

@@ -612,7 +722,7 @@ pub async fn attach_tenant(
            broker_client,
            remote_storage: Some(remote_storage),
        };
-        let attached_tenant = schedule_local_tenant_processing(conf, &tenant_dir, resources, None, &TENANTS, ctx)?;
+        let attached_tenant = schedule_local_tenant_processing(conf, tenant_id, &tenant_dir, generation, resources, None, &TENANTS, ctx)?;
        // TODO: tenant object & its background loops remain, untracked in tenant map, if we fail here.
        //      See https://github.com/neondatabase/neon/issues/4233

@@ -645,12 +755,13 @@ pub enum TenantMapInsertError {
 ///
 /// NB: the closure should return quickly because the current implementation of tenants map
 /// serializes access through an `RwLock`.
-async fn tenant_map_insert<F>(
+async fn tenant_map_insert<F, R>(
    tenant_id: TenantId,
    insert_fn: F,
 ) -> Result<Arc<Tenant>, TenantMapInsertError>
 where
-    F: FnOnce() -> anyhow::Result<Arc<Tenant>>,
+    F: FnOnce() -> R,
+    R: std::future::Future<Output = anyhow::Result<Arc<Tenant>>>,
 {
    let mut guard = TENANTS.write().await;
    let m = match &mut *guard {
@@ -663,7 +774,7 @@ where
            tenant_id,
            e.get().current_state(),
        )),
-        hash_map::Entry::Vacant(v) => match insert_fn() {
+        hash_map::Entry::Vacant(v) => match insert_fn().await {
            Ok(tenant) => {
                v.insert(tenant.clone());
                Ok(tenant)
--- a/pageserver/src/tenant/par_fsync.rs
+++ b/pageserver/src/tenant/par_fsync.rs
@@ -4,10 +4,9 @@ use std::{
    sync::atomic::{AtomicUsize, Ordering},
 };

-use crate::virtual_file::VirtualFile;
-
 fn fsync_path(path: &Path) -> io::Result<()> {
-    let file = VirtualFile::open(path)?;
+    // TODO use VirtualFile::fsync_all once we fully go async.
+    let file = std::fs::File::open(path)?;
    file.sync_all()
 }

--- a/pageserver/src/tenant/remote_timeline_client.rs
+++ b/pageserver/src/tenant/remote_timeline_client.rs
@@ -216,7 +216,7 @@ use utils::backoff::{
 };

 use std::collections::{HashMap, VecDeque};
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicU32, Ordering};
 use std::sync::{Arc, Mutex};

@@ -235,6 +235,7 @@ use crate::task_mgr::shutdown_token;
 use crate::tenant::debug_assert_current_span_has_tenant_and_timeline_id;
 use crate::tenant::remote_timeline_client::index::LayerFileMetadata;
 use crate::tenant::upload_queue::Delete;
+use crate::tenant::TIMELINES_SEGMENT_NAME;
 use crate::{
    config::PageServerConf,
    task_mgr,
@@ -252,6 +253,7 @@ use self::index::IndexPart;

 use super::storage_layer::LayerFileName;
 use super::upload_queue::SetDeletedFlagProgress;
+use super::Generation;

 // Occasional network issues and such can cause remote operations to fail, and
 // that's expected. If a download fails, we log it at info-level, and retry.
@@ -315,6 +317,7 @@ pub struct RemoteTimelineClient {

    tenant_id: TenantId,
    timeline_id: TimelineId,
+    generation: Generation,

    upload_queue: Mutex<UploadQueue>,

@@ -335,12 +338,19 @@ impl RemoteTimelineClient {
        conf: &'static PageServerConf,
        tenant_id: TenantId,
        timeline_id: TimelineId,
+        generation: Generation,
    ) -> RemoteTimelineClient {
        RemoteTimelineClient {
            conf,
-            runtime: BACKGROUND_RUNTIME.handle().to_owned(),
+            runtime: if cfg!(test) {
+                // remote_timeline_client.rs tests rely on current-thread runtime
+                tokio::runtime::Handle::current()
+            } else {
+                BACKGROUND_RUNTIME.handle().clone()
+            },
            tenant_id,
            timeline_id,
+            generation,
            storage_impl: remote_storage,
            upload_queue: Mutex::new(UploadQueue::Uninitialized),
            metrics: Arc::new(RemoteTimelineClientMetrics::new(&tenant_id, &timeline_id)),
@@ -449,10 +459,10 @@ impl RemoteTimelineClient {
        );

        let index_part = download::download_index_part(
-            self.conf,
            &self.storage_impl,
            &self.tenant_id,
            &self.timeline_id,
+            self.generation,
        )
        .measure_remote_op(
            self.tenant_id,
@@ -650,22 +660,41 @@ impl RemoteTimelineClient {
        // from latest_files, but not yet scheduled for deletion. Use a closure
        // to syntactically forbid ? or bail! calls here.
        let no_bail_here = || {
-            for name in names {
-                if upload_queue.latest_files.remove(name).is_some() {
-                    upload_queue.latest_files_changes_since_metadata_upload_scheduled += 1;
-                }
-            }
+            // Decorate our list of names with each name's generation, dropping
+            // makes that are unexpectedly missing from our metadata.
+            let with_generations: Vec<_> = names
+                .iter()
+                .filter_map(|name| {
+                    // Remove from latest_files, learning the file's remote generation in the process
+                    let meta = upload_queue.latest_files.remove(name);
+
+                    if let Some(meta) = meta {
+                        upload_queue.latest_files_changes_since_metadata_upload_scheduled += 1;
+                        Some((name, meta.generation))
+                    } else {
+                        // This can only happen if we forgot to to schedule the file upload
+                        // before scheduling the delete. Log it because it is a rare/strange
+                        // situation, and in case something is misbehaving, we'd like to know which
+                        // layers experienced this.
+                        info!(
+                            "Deleting layer {name} not found in latest_files list, never uploaded?"
+                        );
+                        None
+                    }
+                })
+                .collect();

            if upload_queue.latest_files_changes_since_metadata_upload_scheduled > 0 {
                self.schedule_index_upload(upload_queue, metadata);
            }

            // schedule the actual deletions
-            for name in names {
+            for (name, generation) in with_generations {
                let op = UploadOp::Delete(Delete {
                    file_kind: RemoteOpFileKind::Layer,
                    layer_file_name: name.clone(),
                    scheduled_from_timeline_delete: false,
+                    generation,
                });
                self.calls_unfinished_metric_begin(&op);
                upload_queue.queued_operations.push_back(op);
@@ -761,10 +790,10 @@ impl RemoteTimelineClient {
        backoff::retry(
            || {
                upload::upload_index_part(
-                    self.conf,
                    &self.storage_impl,
                    &self.tenant_id,
                    &self.timeline_id,
+                    self.generation,
                    &index_part_with_deleted_at,
                )
            },
@@ -822,12 +851,14 @@ impl RemoteTimelineClient {
                .reserve(stopped.upload_queue_for_deletion.latest_files.len());

            // schedule the actual deletions
-            for name in stopped.upload_queue_for_deletion.latest_files.keys() {
+            for (name, meta) in &stopped.upload_queue_for_deletion.latest_files {
                let op = UploadOp::Delete(Delete {
                    file_kind: RemoteOpFileKind::Layer,
                    layer_file_name: name.clone(),
                    scheduled_from_timeline_delete: true,
+                    generation: meta.generation,
                });
+
                self.calls_unfinished_metric_begin(&op);
                stopped
                    .upload_queue_for_deletion
@@ -850,8 +881,7 @@ impl RemoteTimelineClient {

        // Do not delete index part yet, it is needed for possible retry. If we remove it first
        // and retry will arrive to different pageserver there wont be any traces of it on remote storage
-        let timeline_path = self.conf.timeline_path(&self.tenant_id, &self.timeline_id);
-        let timeline_storage_path = self.conf.remote_path(&timeline_path)?;
+        let timeline_storage_path = remote_timeline_path(&self.tenant_id, &self.timeline_id);

        let remaining = backoff::retry(
            || async {
@@ -1055,15 +1085,17 @@ impl RemoteTimelineClient {

            let upload_result: anyhow::Result<()> = match &task.op {
                UploadOp::UploadLayer(ref layer_file_name, ref layer_metadata) => {
-                    let path = &self
+                    let path = self
                        .conf
                        .timeline_path(&self.tenant_id, &self.timeline_id)
                        .join(layer_file_name.file_name());
+
                    upload::upload_timeline_layer(
                        self.conf,
                        &self.storage_impl,
-                        path,
+                        &path,
                        layer_metadata,
+                        self.generation,
                    )
                    .measure_remote_op(
                        self.tenant_id,
@@ -1085,10 +1117,10 @@ impl RemoteTimelineClient {
                    };

                    let res = upload::upload_index_part(
-                        self.conf,
                        &self.storage_impl,
                        &self.tenant_id,
                        &self.timeline_id,
+                        self.generation,
                        index_part,
                    )
                    .measure_remote_op(
@@ -1113,7 +1145,7 @@ impl RemoteTimelineClient {
                        .conf
                        .timeline_path(&self.tenant_id, &self.timeline_id)
                        .join(delete.layer_file_name.file_name());
-                    delete::delete_layer(self.conf, &self.storage_impl, path)
+                    delete::delete_layer(self.conf, &self.storage_impl, path, delete.generation)
                        .measure_remote_op(
                            self.tenant_id,
                            self.timeline_id,
@@ -1360,6 +1392,95 @@ impl RemoteTimelineClient {
    }
 }

+pub fn remote_timelines_path(tenant_id: &TenantId) -> RemotePath {
+    let path = format!("tenants/{tenant_id}/{TIMELINES_SEGMENT_NAME}");
+    RemotePath::from_string(&path).expect("Failed to construct path")
+}
+
+pub fn remote_timeline_path(tenant_id: &TenantId, timeline_id: &TimelineId) -> RemotePath {
+    remote_timelines_path(tenant_id).join(&PathBuf::from(timeline_id.to_string()))
+}
+
+pub fn remote_layer_path(
+    tenant_id: &TenantId,
+    timeline_id: &TimelineId,
+    layer_file_name: &LayerFileName,
+    layer_meta: &LayerFileMetadata,
+) -> RemotePath {
+    // Generation-aware key format
+    let path = format!(
+        "tenants/{tenant_id}/{TIMELINES_SEGMENT_NAME}/{timeline_id}/{0}{1}",
+        layer_file_name.file_name(),
+        layer_meta.generation.get_suffix()
+    );
+
+    RemotePath::from_string(&path).expect("Failed to construct path")
+}
+
+pub fn remote_index_path(
+    tenant_id: &TenantId,
+    timeline_id: &TimelineId,
+    generation: Generation,
+) -> RemotePath {
+    RemotePath::from_string(&format!(
+        "tenants/{tenant_id}/{TIMELINES_SEGMENT_NAME}/{timeline_id}/{0}{1}",
+        IndexPart::FILE_NAME,
+        generation.get_suffix()
+    ))
+    .expect("Failed to construct path")
+}
+
+/// Given the key of an index, parse out the generation part of the name
+pub(crate) fn parse_remote_index_path(path: RemotePath) -> Option<Generation> {
+    let file_name = match path.get_path().file_name() {
+        Some(f) => f,
+        None => {
+            // Unexpected: we should be seeing index_part.json paths only
+            tracing::warn!("Malformed index key {}", path);
+            return None;
+        }
+    };
+
+    let file_name_str = match file_name.to_str() {
+        Some(s) => s,
+        None => {
+            tracing::warn!("Malformed index key {:?}", path);
+            return None;
+        }
+    };
+    match file_name_str.split_once('-') {
+        Some((_, gen_suffix)) => Generation::parse_suffix(gen_suffix),
+        None => None,
+    }
+}
+
+/// Files on the remote storage are stored with paths, relative to the workdir.
+/// That path includes in itself both tenant and timeline ids, allowing to have a unique remote storage path.
+///
+/// Errors if the path provided does not start from pageserver's workdir.
+pub fn remote_path(
+    conf: &PageServerConf,
+    local_path: &Path,
+    generation: Generation,
+) -> anyhow::Result<RemotePath> {
+    let stripped = local_path
+        .strip_prefix(&conf.workdir)
+        .context("Failed to strip workdir prefix")?;
+
+    let suffixed = format!(
+        "{0}{1}",
+        stripped.to_string_lossy(),
+        generation.get_suffix()
+    );
+
+    RemotePath::new(&PathBuf::from(suffixed)).with_context(|| {
+        format!(
+            "to resolve remote part of path {:?} for base {:?}",
+            local_path, conf.workdir
+        )
+    })
+}
+
 #[cfg(test)]
 mod tests {
    use super::*;
@@ -1367,15 +1488,12 @@ mod tests {
        context::RequestContext,
        tenant::{
            harness::{TenantHarness, TIMELINE_ID},
-            Tenant, Timeline,
+            Generation, Tenant, Timeline,
        },
        DEFAULT_PG_VERSION,
    };
-    use remote_storage::{RemoteStorageConfig, RemoteStorageKind};
-    use std::{
-        collections::HashSet,
-        path::{Path, PathBuf},
-    };
+
+    use std::{collections::HashSet, path::Path};
    use utils::lsn::Lsn;

    pub(super) fn dummy_contents(name: &str) -> Vec<u8> {
@@ -1409,8 +1527,11 @@ mod tests {
        assert_eq!(avec, bvec);
    }

-    fn assert_remote_files(expected: &[&str], remote_path: &Path) {
-        let mut expected: Vec<String> = expected.iter().map(|x| String::from(*x)).collect();
+    fn assert_remote_files(expected: &[&str], remote_path: &Path, generation: Generation) {
+        let mut expected: Vec<String> = expected
+            .iter()
+            .map(|x| format!("{}{}", x, generation.get_suffix()))
+            .collect();
        expected.sort();

        let mut found: Vec<String> = Vec::new();
@@ -1429,8 +1550,6 @@ mod tests {
        tenant: Arc<Tenant>,
        timeline: Arc<Timeline>,
        tenant_ctx: RequestContext,
-        remote_fs_dir: PathBuf,
-        client: Arc<RemoteTimelineClient>,
    }

    impl TestSetup {
@@ -1440,51 +1559,44 @@ mod tests {
            let harness = TenantHarness::create(test_name)?;
            let (tenant, ctx) = harness.load().await;

-            // create an empty timeline directory
            let timeline = tenant
                .create_test_timeline(TIMELINE_ID, Lsn(8), DEFAULT_PG_VERSION, &ctx)
                .await?;

-            let remote_fs_dir = harness.conf.workdir.join("remote_fs");
-            std::fs::create_dir_all(remote_fs_dir)?;
-            let remote_fs_dir = std::fs::canonicalize(harness.conf.workdir.join("remote_fs"))?;
-
-            let storage_config = RemoteStorageConfig {
-                max_concurrent_syncs: std::num::NonZeroUsize::new(
-                    remote_storage::DEFAULT_REMOTE_STORAGE_MAX_CONCURRENT_SYNCS,
-                )
-                .unwrap(),
-                max_sync_errors: std::num::NonZeroU32::new(
-                    remote_storage::DEFAULT_REMOTE_STORAGE_MAX_SYNC_ERRORS,
-                )
-                .unwrap(),
-                storage: RemoteStorageKind::LocalFs(remote_fs_dir.clone()),
-            };
-
-            let storage = GenericRemoteStorage::from_config(&storage_config).unwrap();
-
-            let client = Arc::new(RemoteTimelineClient {
-                conf: harness.conf,
-                runtime: tokio::runtime::Handle::current(),
-                tenant_id: harness.tenant_id,
-                timeline_id: TIMELINE_ID,
-                storage_impl: storage,
-                upload_queue: Mutex::new(UploadQueue::Uninitialized),
-                metrics: Arc::new(RemoteTimelineClientMetrics::new(
-                    &harness.tenant_id,
-                    &TIMELINE_ID,
-                )),
-            });
-
            Ok(Self {
                harness,
                tenant,
                timeline,
                tenant_ctx: ctx,
-                remote_fs_dir,
-                client,
            })
        }
+
+        /// Construct a RemoteTimelineClient in an arbitrary generation
+        fn build_client(&self, generation: Generation) -> Arc<RemoteTimelineClient> {
+            Arc::new(RemoteTimelineClient {
+                conf: self.harness.conf,
+                runtime: tokio::runtime::Handle::current(),
+                tenant_id: self.harness.tenant_id,
+                timeline_id: TIMELINE_ID,
+                generation,
+                storage_impl: self.harness.remote_storage.clone(),
+                upload_queue: Mutex::new(UploadQueue::Uninitialized),
+                metrics: Arc::new(RemoteTimelineClientMetrics::new(
+                    &self.harness.tenant_id,
+                    &TIMELINE_ID,
+                )),
+            })
+        }
+
+        /// A tracing::Span that satisfies remote_timeline_client methods that assert tenant_id
+        /// and timeline_id are present.
+        fn span(&self) -> tracing::Span {
+            tracing::info_span!(
+                "test",
+                tenant_id = %self.harness.tenant_id,
+                timeline_id = %TIMELINE_ID
+            )
+        }
    }

    // Test scheduling
@@ -1504,27 +1616,44 @@ mod tests {
        // Schedule another deletion. Check that it's launched immediately.
        // Schedule index upload. Check that it's queued

+        let test_setup = TestSetup::new("upload_scheduling").await.unwrap();
+        let span = test_setup.span();
+        let _guard = span.enter();
+
        let TestSetup {
            harness,
            tenant: _tenant,
-            timeline: _timeline,
+            timeline,
            tenant_ctx: _tenant_ctx,
-            remote_fs_dir,
-            client,
-        } = TestSetup::new("upload_scheduling").await.unwrap();
+        } = test_setup;
+
+        let client = timeline.remote_client.as_ref().unwrap();
+
+        // Download back the index.json, and check that the list of files is correct
+        let initial_index_part = match client.download_index_file().await.unwrap() {
+            MaybeDeletedIndexPart::IndexPart(index_part) => index_part,
+            MaybeDeletedIndexPart::Deleted(_) => panic!("unexpectedly got deleted index part"),
+        };
+        let initial_layers = initial_index_part
+            .layer_metadata
+            .keys()
+            .map(|f| f.to_owned())
+            .collect::<HashSet<LayerFileName>>();
+        let initial_layer = {
+            assert!(initial_layers.len() == 1);
+            initial_layers.into_iter().next().unwrap()
+        };

        let timeline_path = harness.timeline_path(&TIMELINE_ID);

        println!("workdir: {}", harness.conf.workdir.display());

-        let remote_timeline_dir =
-            remote_fs_dir.join(timeline_path.strip_prefix(&harness.conf.workdir).unwrap());
+        let remote_timeline_dir = harness
+            .remote_fs_dir
+            .join(timeline_path.strip_prefix(&harness.conf.workdir).unwrap());
        println!("remote_timeline_dir: {}", remote_timeline_dir.display());

-        let metadata = dummy_metadata(Lsn(0x10));
-        client
-            .init_upload_queue_for_empty_remote(&metadata)
-            .unwrap();
+        let generation = harness.generation;

        // Create a couple of dummy files,  schedule upload for them
        let layer_file_name_1: LayerFileName = "000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51".parse().unwrap();
@@ -1545,13 +1674,13 @@ mod tests {
        client
            .schedule_layer_file_upload(
                &layer_file_name_1,
-                &LayerFileMetadata::new(content_1.len() as u64),
+                &LayerFileMetadata::new(content_1.len() as u64, generation),
            )
            .unwrap();
        client
            .schedule_layer_file_upload(
                &layer_file_name_2,
-                &LayerFileMetadata::new(content_2.len() as u64),
+                &LayerFileMetadata::new(content_2.len() as u64, generation),
            )
            .unwrap();

@@ -1605,6 +1734,7 @@ mod tests {
                .map(|f| f.to_owned())
                .collect(),
            &[
+                &initial_layer.file_name(),
                &layer_file_name_1.file_name(),
                &layer_file_name_2.file_name(),
            ],
@@ -1615,7 +1745,7 @@ mod tests {
        client
            .schedule_layer_file_upload(
                &layer_file_name_3,
-                &LayerFileMetadata::new(content_3.len() as u64),
+                &LayerFileMetadata::new(content_3.len() as u64, generation),
            )
            .unwrap();
        client
@@ -1634,11 +1764,13 @@ mod tests {
        }
        assert_remote_files(
            &[
+                &initial_layer.file_name(),
                &layer_file_name_1.file_name(),
                &layer_file_name_2.file_name(),
                "index_part.json",
            ],
            &remote_timeline_dir,
+            generation,
        );

        // Finish them
@@ -1646,11 +1778,13 @@ mod tests {

        assert_remote_files(
            &[
+                &initial_layer.file_name(),
                &layer_file_name_2.file_name(),
                &layer_file_name_3.file_name(),
                "index_part.json",
            ],
            &remote_timeline_dir,
+            generation,
        );
    }

@@ -1661,16 +1795,10 @@ mod tests {
        let TestSetup {
            harness,
            tenant: _tenant,
-            timeline: _timeline,
-            client,
+            timeline,
            ..
        } = TestSetup::new("metrics").await.unwrap();
-
-        let metadata = dummy_metadata(Lsn(0x10));
-        client
-            .init_upload_queue_for_empty_remote(&metadata)
-            .unwrap();
-
+        let client = timeline.remote_client.as_ref().unwrap();
        let timeline_path = harness.timeline_path(&TIMELINE_ID);

        let layer_file_name_1: LayerFileName = "000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51".parse().unwrap();
@@ -1681,11 +1809,20 @@ mod tests {
        )
        .unwrap();

-        #[derive(Debug, PartialEq)]
+        #[derive(Debug, PartialEq, Clone, Copy)]
        struct BytesStartedFinished {
            started: Option<usize>,
            finished: Option<usize>,
        }
+        impl std::ops::Add for BytesStartedFinished {
+            type Output = Self;
+            fn add(self, rhs: Self) -> Self::Output {
+                Self {
+                    started: self.started.map(|v| v + rhs.started.unwrap_or(0)),
+                    finished: self.finished.map(|v| v + rhs.finished.unwrap_or(0)),
+                }
+            }
+        }
        let get_bytes_started_stopped = || {
            let started = client
                .metrics
@@ -1702,45 +1839,140 @@ mod tests {
        };

        // Test
+        tracing::info!("now doing actual test");

-        let init = get_bytes_started_stopped();
+        let actual_a = get_bytes_started_stopped();

        client
            .schedule_layer_file_upload(
                &layer_file_name_1,
-                &LayerFileMetadata::new(content_1.len() as u64),
+                &LayerFileMetadata::new(content_1.len() as u64, harness.generation),
            )
            .unwrap();

-        let pre = get_bytes_started_stopped();
+        let actual_b = get_bytes_started_stopped();

        client.wait_completion().await.unwrap();

-        let post = get_bytes_started_stopped();
+        let actual_c = get_bytes_started_stopped();

        // Validate

-        assert_eq!(
-            init,
-            BytesStartedFinished {
-                started: None,
-                finished: None
-            }
-        );
-        assert_eq!(
-            pre,
-            BytesStartedFinished {
+        let expected_b = actual_a
+            + BytesStartedFinished {
                started: Some(content_1.len()),
                // assert that the _finished metric is created eagerly so that subtractions work on first sample
                finished: Some(0),
-            }
-        );
-        assert_eq!(
-            post,
-            BytesStartedFinished {
+            };
+        assert_eq!(actual_b, expected_b);
+
+        let expected_c = actual_a
+            + BytesStartedFinished {
                started: Some(content_1.len()),
-                finished: Some(content_1.len())
-            }
+                finished: Some(content_1.len()),
+            };
+        assert_eq!(actual_c, expected_c);
+    }
+
+    async fn inject_index_part(test_state: &TestSetup, generation: Generation) -> IndexPart {
+        // An empty IndexPart, just sufficient to ensure deserialization will succeed
+        let example_metadata = TimelineMetadata::example();
+        let example_index_part = IndexPart::new(
+            HashMap::new(),
+            example_metadata.disk_consistent_lsn(),
+            example_metadata,
        );
+
+        let index_part_bytes = serde_json::to_vec(&example_index_part).unwrap();
+
+        let timeline_path = test_state.harness.timeline_path(&TIMELINE_ID);
+        let remote_timeline_dir = test_state.harness.remote_fs_dir.join(
+            timeline_path
+                .strip_prefix(&test_state.harness.conf.workdir)
+                .unwrap(),
+        );
+
+        std::fs::create_dir_all(remote_timeline_dir).expect("creating test dir should work");
+
+        let index_path = test_state.harness.remote_fs_dir.join(
+            remote_index_path(&test_state.harness.tenant_id, &TIMELINE_ID, generation).get_path(),
+        );
+        eprintln!("Writing {}", index_path.display());
+        std::fs::write(&index_path, index_part_bytes).unwrap();
+        example_index_part
+    }
+
+    /// Assert that when a RemoteTimelineclient in generation `get_generation` fetches its
+    /// index, the IndexPart returned is equal to `expected`
+    async fn assert_got_index_part(
+        test_state: &TestSetup,
+        get_generation: Generation,
+        expected: &IndexPart,
+    ) {
+        let client = test_state.build_client(get_generation);
+
+        let download_r = client
+            .download_index_file()
+            .await
+            .expect("download should always succeed");
+        assert!(matches!(download_r, MaybeDeletedIndexPart::IndexPart(_)));
+        match download_r {
+            MaybeDeletedIndexPart::IndexPart(index_part) => {
+                assert_eq!(&index_part, expected);
+            }
+            MaybeDeletedIndexPart::Deleted(_index_part) => panic!("Test doesn't set deleted_at"),
+        }
+    }
+
+    #[tokio::test]
+    async fn index_part_download_simple() -> anyhow::Result<()> {
+        let test_state = TestSetup::new("index_part_download_simple").await.unwrap();
+        let span = test_state.span();
+        let _guard = span.enter();
+
+        // Simple case: we are in generation N, load the index from generation N - 1
+        let generation_n = 5;
+        let injected = inject_index_part(&test_state, Generation::new(generation_n - 1)).await;
+
+        assert_got_index_part(&test_state, Generation::new(generation_n), &injected).await;
+
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn index_part_download_ordering() -> anyhow::Result<()> {
+        let test_state = TestSetup::new("index_part_download_ordering")
+            .await
+            .unwrap();
+
+        let span = test_state.span();
+        let _guard = span.enter();
+
+        // A generation-less IndexPart exists in the bucket, we should find it
+        let generation_n = 5;
+        let injected_none = inject_index_part(&test_state, Generation::none()).await;
+        assert_got_index_part(&test_state, Generation::new(generation_n), &injected_none).await;
+
+        // If a more recent-than-none generation exists, we should prefer to load that
+        let injected_1 = inject_index_part(&test_state, Generation::new(1)).await;
+        assert_got_index_part(&test_state, Generation::new(generation_n), &injected_1).await;
+
+        // If a more-recent-than-me generation exists, we should ignore it.
+        let _injected_10 = inject_index_part(&test_state, Generation::new(10)).await;
+        assert_got_index_part(&test_state, Generation::new(generation_n), &injected_1).await;
+
+        // If a directly previous generation exists, _and_ an index exists in my own
+        // generation, I should prefer my own generation.
+        let _injected_prev =
+            inject_index_part(&test_state, Generation::new(generation_n - 1)).await;
+        let injected_current = inject_index_part(&test_state, Generation::new(generation_n)).await;
+        assert_got_index_part(
+            &test_state,
+            Generation::new(generation_n),
+            &injected_current,
+        )
+        .await;
+
+        Ok(())
    }
 }
--- a/pageserver/src/tenant/remote_timeline_client/delete.rs
+++ b/pageserver/src/tenant/remote_timeline_client/delete.rs
@@ -5,25 +5,30 @@ use tracing::debug;

 use remote_storage::GenericRemoteStorage;

-use crate::config::PageServerConf;
+use crate::{
+    config::PageServerConf,
+    tenant::{remote_timeline_client::remote_path, Generation},
+};

 pub(super) async fn delete_layer<'a>(
    conf: &'static PageServerConf,
    storage: &'a GenericRemoteStorage,
    local_layer_path: &'a Path,
+    generation: Generation,
 ) -> anyhow::Result<()> {
    fail::fail_point!("before-delete-layer", |_| {
        anyhow::bail!("failpoint before-delete-layer")
    });
    debug!("Deleting layer from remote storage: {local_layer_path:?}",);

-    let path_to_delete = conf.remote_path(local_layer_path)?;
+    let path_to_delete = remote_path(conf, local_layer_path, generation)?;

    // We don't want to print an error if the delete failed if the file has
    // already been deleted. Thankfully, in this situation S3 already
    // does not yield an error. While OS-provided local file system APIs do yield
    // errors, we avoid them in the `LocalFs` wrapper.
-    storage.delete(&path_to_delete).await.with_context(|| {
-        format!("Failed to delete remote layer from storage at {path_to_delete:?}")
-    })
+    storage
+        .delete(&path_to_delete)
+        .await
+        .with_context(|| format!("delete remote layer from storage at {path_to_delete:?}"))
 }
--- a/pageserver/src/tenant/remote_timeline_client/download.rs
+++ b/pageserver/src/tenant/remote_timeline_client/download.rs
@@ -15,14 +15,19 @@ use tokio_util::sync::CancellationToken;
 use utils::{backoff, crashsafe};

 use crate::config::PageServerConf;
+use crate::tenant::remote_timeline_client::{remote_layer_path, remote_timelines_path};
 use crate::tenant::storage_layer::LayerFileName;
 use crate::tenant::timeline::span::debug_assert_current_span_has_tenant_and_timeline_id;
+use crate::tenant::Generation;
 use remote_storage::{DownloadError, GenericRemoteStorage};
 use utils::crashsafe::path_with_suffix_extension;
 use utils::id::{TenantId, TimelineId};

 use super::index::{IndexPart, LayerFileMetadata};
-use super::{FAILED_DOWNLOAD_WARN_THRESHOLD, FAILED_REMOTE_OP_RETRIES};
+use super::{
+    parse_remote_index_path, remote_index_path, FAILED_DOWNLOAD_WARN_THRESHOLD,
+    FAILED_REMOTE_OP_RETRIES,
+};

 static MAX_DOWNLOAD_DURATION: Duration = Duration::from_secs(120);

@@ -41,13 +46,11 @@ pub async fn download_layer_file<'a>(
 ) -> Result<u64, DownloadError> {
    debug_assert_current_span_has_tenant_and_timeline_id();

-    let timeline_path = conf.timeline_path(&tenant_id, &timeline_id);
+    let local_path = conf
+        .timeline_path(&tenant_id, &timeline_id)
+        .join(layer_file_name.file_name());

-    let local_path = timeline_path.join(layer_file_name.file_name());
-
-    let remote_path = conf
-        .remote_path(&local_path)
-        .map_err(DownloadError::Other)?;
+    let remote_path = remote_layer_path(&tenant_id, &timeline_id, layer_file_name, layer_metadata);

    // Perform a rename inspired by durable_rename from file_utils.c.
    // The sequence:
@@ -64,33 +67,43 @@ pub async fn download_layer_file<'a>(
    let (mut destination_file, bytes_amount) = download_retry(
        || async {
            // TODO: this doesn't use the cached fd for some reason?
-            let mut destination_file = fs::File::create(&temp_file_path).await.with_context(|| {
-                format!(
-                    "create a destination file for layer '{}'",
-                    temp_file_path.display()
-                )
-            })
-            .map_err(DownloadError::Other)?;
-            let mut download = storage.download(&remote_path).await.with_context(|| {
-                format!(
+            let mut destination_file = fs::File::create(&temp_file_path)
+                .await
+                .with_context(|| {
+                    format!(
+                        "create a destination file for layer '{}'",
+                        temp_file_path.display()
+                    )
+                })
+                .map_err(DownloadError::Other)?;
+            let mut download = storage
+                .download(&remote_path)
+                .await
+                .with_context(|| {
+                    format!(
                    "open a download stream for layer with remote storage path '{remote_path:?}'"
                )
-            })
-            .map_err(DownloadError::Other)?;
-
-            let bytes_amount = tokio::time::timeout(MAX_DOWNLOAD_DURATION, tokio::io::copy(&mut download.download_stream, &mut destination_file))
-                .await
-                .map_err(|e| DownloadError::Other(anyhow::anyhow!("Timed out  {:?}", e)))?
-                .with_context(|| {
-                    format!("Failed to download layer with remote storage path '{remote_path:?}' into file {temp_file_path:?}")
                })
                .map_err(DownloadError::Other)?;

-            Ok((destination_file, bytes_amount))
+            let bytes_amount = tokio::time::timeout(
+                MAX_DOWNLOAD_DURATION,
+                tokio::io::copy(&mut download.download_stream, &mut destination_file),
+            )
+            .await
+            .map_err(|e| DownloadError::Other(anyhow::anyhow!("Timed out  {:?}", e)))?
+            .with_context(|| {
+                format!(
+                    "download layer at remote path '{remote_path:?}' into file {temp_file_path:?}"
+                )
+            })
+            .map_err(DownloadError::Other)?;

+            Ok((destination_file, bytes_amount))
        },
        &format!("download {remote_path:?}"),
-    ).await?;
+    )
+    .await?;

    // Tokio doc here: https://docs.rs/tokio/1.17.0/tokio/fs/struct.File.html states that:
    // A file will not be closed immediately when it goes out of scope if there are any IO operations
@@ -103,12 +116,7 @@ pub async fn download_layer_file<'a>(
    destination_file
        .flush()
        .await
-        .with_context(|| {
-            format!(
-                "failed to flush source file at {}",
-                temp_file_path.display()
-            )
-        })
+        .with_context(|| format!("flush source file at {}", temp_file_path.display()))
        .map_err(DownloadError::Other)?;

    let expected = layer_metadata.file_size();
@@ -139,17 +147,12 @@ pub async fn download_layer_file<'a>(

    fs::rename(&temp_file_path, &local_path)
        .await
-        .with_context(|| {
-            format!(
-                "Could not rename download layer file to {}",
-                local_path.display(),
-            )
-        })
+        .with_context(|| format!("rename download layer file to {}", local_path.display(),))
        .map_err(DownloadError::Other)?;

    crashsafe::fsync_async(&local_path)
        .await
-        .with_context(|| format!("Could not fsync layer file {}", local_path.display(),))
+        .with_context(|| format!("fsync layer file {}", local_path.display(),))
        .map_err(DownloadError::Other)?;

    tracing::debug!("download complete: {}", local_path.display());
@@ -173,21 +176,19 @@ pub fn is_temp_download_file(path: &Path) -> bool {
 }

 /// List timelines of given tenant in remote storage
-pub async fn list_remote_timelines<'a>(
-    storage: &'a GenericRemoteStorage,
-    conf: &'static PageServerConf,
+pub async fn list_remote_timelines(
+    storage: &GenericRemoteStorage,
    tenant_id: TenantId,
 ) -> anyhow::Result<HashSet<TimelineId>> {
-    let tenant_path = conf.timelines_path(&tenant_id);
-    let tenant_storage_path = conf.remote_path(&tenant_path)?;
+    let remote_path = remote_timelines_path(&tenant_id);

    fail::fail_point!("storage-sync-list-remote-timelines", |_| {
        anyhow::bail!("storage-sync-list-remote-timelines");
    });

    let timelines = download_retry(
-        || storage.list_prefixes(Some(&tenant_storage_path)),
-        &format!("list prefixes for {tenant_path:?}"),
+        || storage.list_prefixes(Some(&remote_path)),
+        &format!("list prefixes for {tenant_id}"),
    )
    .await?;

@@ -202,9 +203,9 @@ pub async fn list_remote_timelines<'a>(
            anyhow::anyhow!("failed to get timeline id for remote tenant {tenant_id}")
        })?;

-        let timeline_id: TimelineId = object_name.parse().with_context(|| {
-            format!("failed to parse object name into timeline id '{object_name}'")
-        })?;
+        let timeline_id: TimelineId = object_name
+            .parse()
+            .with_context(|| format!("parse object name into timeline id '{object_name}'"))?;

        // list_prefixes is assumed to return unique names. Ensure this here.
        // NB: it's safer to bail out than warn-log this because the pageserver
@@ -221,22 +222,17 @@ pub async fn list_remote_timelines<'a>(
    Ok(timeline_ids)
 }

-pub(super) async fn download_index_part(
-    conf: &'static PageServerConf,
+async fn do_download_index_part(
    storage: &GenericRemoteStorage,
    tenant_id: &TenantId,
    timeline_id: &TimelineId,
+    index_generation: Generation,
 ) -> Result<IndexPart, DownloadError> {
-    let index_part_path = conf
-        .metadata_path(tenant_id, timeline_id)
-        .with_file_name(IndexPart::FILE_NAME);
-    let part_storage_path = conf
-        .remote_path(&index_part_path)
-        .map_err(DownloadError::BadInput)?;
+    let remote_path = remote_index_path(tenant_id, timeline_id, index_generation);

    let index_part_bytes = download_retry(
        || async {
-            let mut index_part_download = storage.download(&part_storage_path).await?;
+            let mut index_part_download = storage.download(&remote_path).await?;

            let mut index_part_bytes = Vec::new();
            tokio::io::copy(
@@ -244,25 +240,120 @@ pub(super) async fn download_index_part(
                &mut index_part_bytes,
            )
            .await
-            .with_context(|| {
-                format!("Failed to download an index part into file {index_part_path:?}")
-            })
+            .with_context(|| format!("download index part at {remote_path:?}"))
            .map_err(DownloadError::Other)?;
            Ok(index_part_bytes)
        },
-        &format!("download {part_storage_path:?}"),
+        &format!("download {remote_path:?}"),
    )
    .await?;

    let index_part: IndexPart = serde_json::from_slice(&index_part_bytes)
-        .with_context(|| {
-            format!("Failed to deserialize index part file into file {index_part_path:?}")
-        })
+        .with_context(|| format!("download index part file at {remote_path:?}"))
        .map_err(DownloadError::Other)?;

    Ok(index_part)
 }

+/// index_part.json objects are suffixed with a generation number, so we cannot
+/// directly GET the latest index part without doing some probing.
+///
+/// In this function we probe for the most recent index in a generation <= our current generation.
+/// See "Finding the remote indices for timelines" in docs/rfcs/025-generation-numbers.md
+#[tracing::instrument(skip_all, fields(generation=?my_generation))]
+pub(super) async fn download_index_part(
+    storage: &GenericRemoteStorage,
+    tenant_id: &TenantId,
+    timeline_id: &TimelineId,
+    my_generation: Generation,
+) -> Result<IndexPart, DownloadError> {
+    debug_assert_current_span_has_tenant_and_timeline_id();
+
+    if my_generation.is_none() {
+        // Operating without generations: just fetch the generation-less path
+        return do_download_index_part(storage, tenant_id, timeline_id, my_generation).await;
+    }
+
+    // Stale case: If we were intentionally attached in a stale generation, there may already be a remote
+    // index in our generation.
+    //
+    // This is an optimization to avoid doing the listing for the general case below.
+    let res = do_download_index_part(storage, tenant_id, timeline_id, my_generation).await;
+    match res {
+        Ok(index_part) => {
+            tracing::debug!(
+                "Found index_part from current generation (this is a stale attachment)"
+            );
+            return Ok(index_part);
+        }
+        Err(DownloadError::NotFound) => {}
+        Err(e) => return Err(e),
+    };
+
+    // Typical case: the previous generation of this tenant was running healthily, and had uploaded
+    // and index part.  We may safely start from this index without doing a listing, because:
+    //  - We checked for current generation case above
+    //  - generations > my_generation are to be ignored
+    //  - any other indices that exist would have an older generation than `previous_gen`, and
+    //    we want to find the most recent index from a previous generation.
+    //
+    // This is an optimization to avoid doing the listing for the general case below.
+    let res =
+        do_download_index_part(storage, tenant_id, timeline_id, my_generation.previous()).await;
+    match res {
+        Ok(index_part) => {
+            tracing::debug!("Found index_part from previous generation");
+            return Ok(index_part);
+        }
+        Err(DownloadError::NotFound) => {
+            tracing::debug!(
+                "No index_part found from previous generation, falling back to listing"
+            );
+        }
+        Err(e) => {
+            return Err(e);
+        }
+    }
+
+    // General case/fallback: if there is no index at my_generation or prev_generation, then list all index_part.json
+    // objects, and select the highest one with a generation <= my_generation.
+    let index_prefix = remote_index_path(tenant_id, timeline_id, Generation::none());
+    let indices = backoff::retry(
+        || async { storage.list_files(Some(&index_prefix)).await },
+        |_| false,
+        FAILED_DOWNLOAD_WARN_THRESHOLD,
+        FAILED_REMOTE_OP_RETRIES,
+        "listing index_part files",
+        // TODO: use a cancellation token (https://github.com/neondatabase/neon/issues/5066)
+        backoff::Cancel::new(CancellationToken::new(), || -> anyhow::Error {
+            unreachable!()
+        }),
+    )
+    .await
+    .map_err(DownloadError::Other)?;
+
+    // General case logic for which index to use: the latest index whose generation
+    // is <= our own.  See "Finding the remote indices for timelines" in docs/rfcs/025-generation-numbers.md
+    let max_previous_generation = indices
+        .into_iter()
+        .filter_map(parse_remote_index_path)
+        .filter(|g| g <= &my_generation)
+        .max();
+
+    match max_previous_generation {
+        Some(g) => {
+            tracing::debug!("Found index_part in generation {g:?}");
+            do_download_index_part(storage, tenant_id, timeline_id, g).await
+        }
+        None => {
+            // Migration from legacy pre-generation state: we have a generation but no prior
+            // attached pageservers did.  Try to load from a no-generation path.
+            tracing::info!("No index_part.json* found");
+            do_download_index_part(storage, tenant_id, timeline_id, Generation::none()).await
+        }
+    }
+}
+
 /// Helper function to handle retries for a download operation.
 ///
 /// Remote operations can fail due to rate limits (IAM, S3), spurious network
--- a/pageserver/src/tenant/remote_timeline_client/index.rs
+++ b/pageserver/src/tenant/remote_timeline_client/index.rs
@@ -2,7 +2,7 @@
 //! Able to restore itself from the storage index parts, that are located in every timeline's remote directory and contain all data about
 //! remote timeline layers and its metadata.

-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;

 use chrono::NaiveDateTime;
 use serde::{Deserialize, Serialize};
@@ -12,6 +12,7 @@ use utils::bin_ser::SerializeError;
 use crate::tenant::metadata::TimelineMetadata;
 use crate::tenant::storage_layer::LayerFileName;
 use crate::tenant::upload_queue::UploadQueueInitialized;
+use crate::tenant::Generation;

 use utils::lsn::Lsn;

@@ -20,22 +21,28 @@ use utils::lsn::Lsn;
 /// Fields have to be `Option`s because remote [`IndexPart`]'s can be from different version, which
 /// might have less or more metadata depending if upgrading or rolling back an upgrade.
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
-#[cfg_attr(test, derive(Default))]
+//#[cfg_attr(test, derive(Default))]
 pub struct LayerFileMetadata {
    file_size: u64,
+
+    pub(crate) generation: Generation,
 }

 impl From<&'_ IndexLayerMetadata> for LayerFileMetadata {
    fn from(other: &IndexLayerMetadata) -> Self {
        LayerFileMetadata {
            file_size: other.file_size,
+            generation: other.generation,
        }
    }
 }

 impl LayerFileMetadata {
-    pub fn new(file_size: u64) -> Self {
-        LayerFileMetadata { file_size }
+    pub fn new(file_size: u64, generation: Generation) -> Self {
+        LayerFileMetadata {
+            file_size,
+            generation,
+        }
    }

    pub fn file_size(&self) -> u64 {
@@ -62,10 +69,6 @@ pub struct IndexPart {
    #[serde(skip_serializing_if = "Option::is_none")]
    pub deleted_at: Option<NaiveDateTime>,

-    /// Legacy field: equal to the keys of `layer_metadata`, only written out for forward compat
-    #[serde(default, skip_deserializing)]
-    timeline_layers: HashSet<LayerFileName>,
-
    /// Per layer file name metadata, which can be present for a present or missing layer file.
    ///
    /// Older versions of `IndexPart` will not have this property or have only a part of metadata
@@ -91,7 +94,12 @@ impl IndexPart {
    /// - 2: added `deleted_at`
    /// - 3: no longer deserialize `timeline_layers` (serialized format is the same, but timeline_layers
    ///      is always generated from the keys of `layer_metadata`)
-    const LATEST_VERSION: usize = 3;
+    /// - 4: timeline_layers is fully removed.
+    const LATEST_VERSION: usize = 4;
+
+    // Versions we may see when reading from a bucket.
+    pub const KNOWN_VERSIONS: &[usize] = &[1, 2, 3, 4];
+
    pub const FILE_NAME: &'static str = "index_part.json";

    pub fn new(
@@ -99,24 +107,30 @@ impl IndexPart {
        disk_consistent_lsn: Lsn,
        metadata: TimelineMetadata,
    ) -> Self {
-        let mut timeline_layers = HashSet::with_capacity(layers_and_metadata.len());
-        let mut layer_metadata = HashMap::with_capacity(layers_and_metadata.len());
-
-        for (remote_name, metadata) in &layers_and_metadata {
-            timeline_layers.insert(remote_name.to_owned());
-            let metadata = IndexLayerMetadata::from(metadata);
-            layer_metadata.insert(remote_name.to_owned(), metadata);
-        }
+        // Transform LayerFileMetadata into IndexLayerMetadata
+        let layer_metadata = layers_and_metadata
+            .into_iter()
+            .map(|(k, v)| (k, IndexLayerMetadata::from(v)))
+            .collect();

        Self {
            version: Self::LATEST_VERSION,
-            timeline_layers,
            layer_metadata,
            disk_consistent_lsn,
            metadata,
            deleted_at: None,
        }
    }
+
+    pub fn get_version(&self) -> usize {
+        self.version
+    }
+
+    /// If you want this under normal operations, read it from self.metadata:
+    /// this method is just for the scrubber to use when validating an index.
+    pub fn get_disk_consistent_lsn(&self) -> Lsn {
+        self.disk_consistent_lsn
+    }
 }

 impl TryFrom<&UploadQueueInitialized> for IndexPart {
@@ -135,15 +149,20 @@ impl TryFrom<&UploadQueueInitialized> for IndexPart {
 }

 /// Serialized form of [`LayerFileMetadata`].
-#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, Default)]
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
 pub struct IndexLayerMetadata {
-    pub(super) file_size: u64,
+    pub file_size: u64,
+
+    #[serde(default = "Generation::none")]
+    #[serde(skip_serializing_if = "Generation::is_none")]
+    pub(super) generation: Generation,
 }

-impl From<&'_ LayerFileMetadata> for IndexLayerMetadata {
-    fn from(other: &'_ LayerFileMetadata) -> Self {
+impl From<LayerFileMetadata> for IndexLayerMetadata {
+    fn from(other: LayerFileMetadata) -> Self {
        IndexLayerMetadata {
            file_size: other.file_size,
+            generation: other.generation,
        }
    }
 }
@@ -168,15 +187,16 @@ mod tests {
        let expected = IndexPart {
            // note this is not verified, could be anything, but exists for humans debugging.. could be the git version instead?
            version: 1,
-            timeline_layers: HashSet::new(),
            layer_metadata: HashMap::from([
                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__0000000001696070-00000000016960E9".parse().unwrap(), IndexLayerMetadata {
                    file_size: 25600000,
+                    generation: Generation::none()
                }),
                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51".parse().unwrap(), IndexLayerMetadata {
                    // serde_json should always parse this but this might be a double with jq for
                    // example.
                    file_size: 9007199254741001,
+                    generation: Generation::none()
                })
            ]),
            disk_consistent_lsn: "0/16960E8".parse::<Lsn>().unwrap(),
@@ -205,15 +225,16 @@ mod tests {
        let expected = IndexPart {
            // note this is not verified, could be anything, but exists for humans debugging.. could be the git version instead?
            version: 1,
-            timeline_layers: HashSet::new(),
            layer_metadata: HashMap::from([
                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__0000000001696070-00000000016960E9".parse().unwrap(), IndexLayerMetadata {
                    file_size: 25600000,
+                    generation: Generation::none()
                }),
                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51".parse().unwrap(), IndexLayerMetadata {
                    // serde_json should always parse this but this might be a double with jq for
                    // example.
                    file_size: 9007199254741001,
+                    generation: Generation::none()
                })
            ]),
            disk_consistent_lsn: "0/16960E8".parse::<Lsn>().unwrap(),
@@ -243,15 +264,16 @@ mod tests {
        let expected = IndexPart {
            // note this is not verified, could be anything, but exists for humans debugging.. could be the git version instead?
            version: 2,
-            timeline_layers: HashSet::new(),
            layer_metadata: HashMap::from([
                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__0000000001696070-00000000016960E9".parse().unwrap(), IndexLayerMetadata {
                    file_size: 25600000,
+                    generation: Generation::none()
                }),
                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51".parse().unwrap(), IndexLayerMetadata {
                    // serde_json should always parse this but this might be a double with jq for
                    // example.
                    file_size: 9007199254741001,
+                    generation: Generation::none()
                })
            ]),
            disk_consistent_lsn: "0/16960E8".parse::<Lsn>().unwrap(),
@@ -276,7 +298,6 @@ mod tests {

        let expected = IndexPart {
            version: 1,
-            timeline_layers: HashSet::new(),
            layer_metadata: HashMap::new(),
            disk_consistent_lsn: "0/2532648".parse::<Lsn>().unwrap(),
            metadata: TimelineMetadata::from_bytes(&[
@@ -309,4 +330,41 @@ mod tests {

        assert_eq!(empty_layers_parsed, expected);
    }
+
+    #[test]
+    fn v4_indexpart_is_parsed() {
+        let example = r#"{
+            "version":4,
+            "layer_metadata":{
+                "000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__0000000001696070-00000000016960E9": { "file_size": 25600000 },
+                "000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51": { "file_size": 9007199254741001 }
+            },
+            "disk_consistent_lsn":"0/16960E8",
+            "metadata_bytes":[113,11,159,210,0,54,0,4,0,0,0,0,1,105,96,232,1,0,0,0,0,1,105,96,112,0,0,0,0,0,0,0,0,0,0,0,0,0,1,105,96,112,0,0,0,0,1,105,96,112,0,0,0,14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],
+            "deleted_at": "2023-07-31T09:00:00.123"
+        }"#;
+
+        let expected = IndexPart {
+            version: 4,
+            layer_metadata: HashMap::from([
+                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__0000000001696070-00000000016960E9".parse().unwrap(), IndexLayerMetadata {
+                    file_size: 25600000,
+                    generation: Generation::none()
+                }),
+                ("000000000000000000000000000000000000-FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF__00000000016B59D8-00000000016B5A51".parse().unwrap(), IndexLayerMetadata {
+                    // serde_json should always parse this but this might be a double with jq for
+                    // example.
+                    file_size: 9007199254741001,
+                    generation: Generation::none()
+                })
+            ]),
+            disk_consistent_lsn: "0/16960E8".parse::<Lsn>().unwrap(),
+            metadata: TimelineMetadata::from_bytes(&[113,11,159,210,0,54,0,4,0,0,0,0,1,105,96,232,1,0,0,0,0,1,105,96,112,0,0,0,0,0,0,0,0,0,0,0,0,0,1,105,96,112,0,0,0,0,1,105,96,112,0,0,0,14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]).unwrap(),
+            deleted_at: Some(chrono::NaiveDateTime::parse_from_str(
+                "2023-07-31T09:00:00.123000000", "%Y-%m-%dT%H:%M:%S.%f").unwrap())
+        };
+
+        let part = serde_json::from_str::<IndexPart>(example).unwrap();
+        assert_eq!(part, expected);
+    }
 }
--- a/pageserver/src/tenant/remote_timeline_client/upload.rs
+++ b/pageserver/src/tenant/remote_timeline_client/upload.rs
@@ -5,7 +5,11 @@ use fail::fail_point;
 use std::{io::ErrorKind, path::Path};
 use tokio::fs;

-use crate::{config::PageServerConf, tenant::remote_timeline_client::index::IndexPart};
+use super::Generation;
+use crate::{
+    config::PageServerConf,
+    tenant::remote_timeline_client::{index::IndexPart, remote_index_path, remote_path},
+};
 use remote_storage::GenericRemoteStorage;
 use utils::id::{TenantId, TimelineId};

@@ -15,10 +19,10 @@ use tracing::info;

 /// Serializes and uploads the given index part data to the remote storage.
 pub(super) async fn upload_index_part<'a>(
-    conf: &'static PageServerConf,
    storage: &'a GenericRemoteStorage,
    tenant_id: &TenantId,
    timeline_id: &TimelineId,
+    generation: Generation,
    index_part: &'a IndexPart,
 ) -> anyhow::Result<()> {
    tracing::trace!("uploading new index part");
@@ -27,20 +31,16 @@ pub(super) async fn upload_index_part<'a>(
        bail!("failpoint before-upload-index")
    });

-    let index_part_bytes = serde_json::to_vec(&index_part)
-        .context("Failed to serialize index part file into bytes")?;
+    let index_part_bytes =
+        serde_json::to_vec(&index_part).context("serialize index part file into bytes")?;
    let index_part_size = index_part_bytes.len();
    let index_part_bytes = tokio::io::BufReader::new(std::io::Cursor::new(index_part_bytes));

-    let index_part_path = conf
-        .metadata_path(tenant_id, timeline_id)
-        .with_file_name(IndexPart::FILE_NAME);
-    let storage_path = conf.remote_path(&index_part_path)?;
-
+    let remote_path = remote_index_path(tenant_id, timeline_id, generation);
    storage
-        .upload_storage_object(Box::new(index_part_bytes), index_part_size, &storage_path)
+        .upload_storage_object(Box::new(index_part_bytes), index_part_size, &remote_path)
        .await
-        .with_context(|| format!("Failed to upload index part for '{tenant_id} / {timeline_id}'"))
+        .with_context(|| format!("upload index part for '{tenant_id} / {timeline_id}'"))
 }

 /// Attempts to upload given layer files.
@@ -52,12 +52,13 @@ pub(super) async fn upload_timeline_layer<'a>(
    storage: &'a GenericRemoteStorage,
    source_path: &'a Path,
    known_metadata: &'a LayerFileMetadata,
+    generation: Generation,
 ) -> anyhow::Result<()> {
    fail_point!("before-upload-layer", |_| {
        bail!("failpoint before-upload-layer")
    });
-    let storage_path = conf.remote_path(source_path)?;

+    let storage_path = remote_path(conf, source_path, generation)?;
    let source_file_res = fs::File::open(&source_path).await;
    let source_file = match source_file_res {
        Ok(source_file) => source_file,
@@ -70,16 +71,15 @@ pub(super) async fn upload_timeline_layer<'a>(
            info!(path = %source_path.display(), "File to upload doesn't exist. Likely the file has been deleted and an upload is not required any more.");
            return Ok(());
        }
-        Err(e) => Err(e)
-            .with_context(|| format!("Failed to open a source file for layer {source_path:?}"))?,
+        Err(e) => {
+            Err(e).with_context(|| format!("open a source file for layer {source_path:?}"))?
+        }
    };

    let fs_size = source_file
        .metadata()
        .await
-        .with_context(|| {
-            format!("Failed to get the source file metadata for layer {source_path:?}")
-        })?
+        .with_context(|| format!("get the source file metadata for layer {source_path:?}"))?
        .len();

    let metadata_size = known_metadata.file_size();
@@ -87,19 +87,13 @@ pub(super) async fn upload_timeline_layer<'a>(
        bail!("File {source_path:?} has its current FS size {fs_size} diferent from initially determined {metadata_size}");
    }

-    let fs_size = usize::try_from(fs_size).with_context(|| {
-        format!("File {source_path:?} size {fs_size} could not be converted to usize")
-    })?;
+    let fs_size = usize::try_from(fs_size)
+        .with_context(|| format!("convert {source_path:?} size {fs_size} usize"))?;

    storage
        .upload(source_file, fs_size, &storage_path, None)
        .await
-        .with_context(|| {
-            format!(
-                "Failed to upload a layer from local path '{}'",
-                source_path.display()
-            )
-        })?;
+        .with_context(|| format!("upload layer from local path '{}'", source_path.display()))?;

    Ok(())
 }
--- a/pageserver/src/tenant/storage_layer/delta_layer.rs
+++ b/pageserver/src/tenant/storage_layer/delta_layer.rs
@@ -28,10 +28,10 @@
 //! "values" part.
 //!
 use crate::config::PageServerConf;
-use crate::context::RequestContext;
+use crate::context::{PageContentKind, RequestContext, RequestContextBuilder};
 use crate::page_cache::PAGE_SZ;
 use crate::repository::{Key, Value, KEY_SIZE};
-use crate::tenant::blob_io::{BlobWriter, WriteBlobWriter};
+use crate::tenant::blob_io::BlobWriter;
 use crate::tenant::block_io::{BlockBuf, BlockCursor, BlockLease, BlockReader, FileBlockReader};
 use crate::tenant::disk_btree::{DiskBtreeBuilder, DiskBtreeReader, VisitDirection};
 use crate::tenant::storage_layer::{
@@ -45,8 +45,7 @@ use pageserver_api::models::{HistoricLayerInfo, LayerAccessKind};
 use rand::{distributions::Alphanumeric, Rng};
 use serde::{Deserialize, Serialize};
 use std::fs::{self, File};
-use std::io::{BufWriter, Write};
-use std::io::{Seek, SeekFrom};
+use std::io::SeekFrom;
 use std::ops::Range;
 use std::os::unix::fs::FileExt;
 use std::path::{Path, PathBuf};
@@ -219,7 +218,7 @@ pub struct DeltaLayerInner {
    index_root_blk: u32,

    /// Reader object for reading blocks from the file.
-    file: FileBlockReader<VirtualFile>,
+    file: FileBlockReader,
 }

 impl AsRef<DeltaLayerInner> for DeltaLayerInner {
@@ -318,11 +317,11 @@ impl DeltaLayer {

        tree_reader.dump().await?;

-        let keys = DeltaLayerInner::load_keys(&inner).await?;
+        let keys = DeltaLayerInner::load_keys(&inner, ctx).await?;

        // A subroutine to dump a single blob
-        async fn dump_blob(val: ValueRef<'_>) -> Result<String> {
-            let buf = val.reader.read_blob(val.blob_ref.pos()).await?;
+        async fn dump_blob(val: ValueRef<'_>, ctx: &RequestContext) -> Result<String> {
+            let buf = val.reader.read_blob(val.blob_ref.pos(), ctx).await?;
            let val = Value::des(&buf)?;
            let desc = match val {
                Value::Image(img) => {
@@ -343,7 +342,7 @@ impl DeltaLayer {

        for entry in keys {
            let DeltaEntry { key, lsn, val, .. } = entry;
-            let desc = match dump_blob(val).await {
+            let desc = match dump_blob(val, ctx).await {
                Ok(desc) => desc,
                Err(err) => {
                    let err: anyhow::Error = err;
@@ -371,7 +370,7 @@ impl DeltaLayer {
            .load(LayerAccessKind::GetValueReconstructData, ctx)
            .await?;
        inner
-            .get_value_reconstruct_data(key, lsn_range, reconstruct_state)
+            .get_value_reconstruct_data(key, lsn_range, reconstruct_state, ctx)
            .await
    }

@@ -454,12 +453,12 @@ impl DeltaLayer {
        self.access_stats.record_access(access_kind, ctx);
        // Quick exit if already loaded
        self.inner
-            .get_or_try_init(|| self.load_inner())
+            .get_or_try_init(|| self.load_inner(ctx))
            .await
            .with_context(|| format!("Failed to load delta layer {}", self.path().display()))
    }

-    async fn load_inner(&self) -> Result<Arc<DeltaLayerInner>> {
+    async fn load_inner(&self, ctx: &RequestContext) -> Result<Arc<DeltaLayerInner>> {
        let path = self.path();

        let summary = match &self.path_or_conf {
@@ -467,7 +466,7 @@ impl DeltaLayer {
            PathOrConf::Path(_) => None,
        };

-        let loaded = DeltaLayerInner::load(&path, summary).await?;
+        let loaded = DeltaLayerInner::load(&path, summary, ctx).await?;

        if let PathOrConf::Path(ref path) = self.path_or_conf {
            // not production code
@@ -555,7 +554,7 @@ impl DeltaLayer {
            .load(LayerAccessKind::KeyIter, ctx)
            .await
            .context("load delta layer keys")?;
-        DeltaLayerInner::load_keys(inner)
+        DeltaLayerInner::load_keys(inner, ctx)
            .await
            .context("Layer index is corrupted")
    }
@@ -583,14 +582,14 @@ struct DeltaLayerWriterInner {

    tree: DiskBtreeBuilder<BlockBuf, DELTA_KEY_SIZE>,

-    blob_writer: WriteBlobWriter<BufWriter<VirtualFile>>,
+    blob_writer: BlobWriter<true>,
 }

 impl DeltaLayerWriterInner {
    ///
    /// Start building a new delta layer.
    ///
-    fn new(
+    async fn new(
        conf: &'static PageServerConf,
        timeline_id: TimelineId,
        tenant_id: TenantId,
@@ -605,11 +604,10 @@ impl DeltaLayerWriterInner {
        // FIXME: throw an error instead?
        let path = DeltaLayer::temp_path_for(conf, &tenant_id, &timeline_id, key_start, &lsn_range);

-        let mut file = VirtualFile::create(&path)?;
+        let mut file = VirtualFile::create(&path).await?;
        // make room for the header block
-        file.seek(SeekFrom::Start(PAGE_SZ as u64))?;
-        let buf_writer = BufWriter::new(file);
-        let blob_writer = WriteBlobWriter::new(buf_writer, PAGE_SZ as u64);
+        file.seek(SeekFrom::Start(PAGE_SZ as u64)).await?;
+        let blob_writer = BlobWriter::new(file, PAGE_SZ as u64);

        // Initialize the b-tree index builder
        let block_buf = BlockBuf::new();
@@ -632,11 +630,12 @@ impl DeltaLayerWriterInner {
    ///
    /// The values must be appended in key, lsn order.
    ///
-    fn put_value(&mut self, key: Key, lsn: Lsn, val: Value) -> anyhow::Result<()> {
+    async fn put_value(&mut self, key: Key, lsn: Lsn, val: Value) -> anyhow::Result<()> {
        self.put_value_bytes(key, lsn, &Value::ser(&val)?, val.will_init())
+            .await
    }

-    fn put_value_bytes(
+    async fn put_value_bytes(
        &mut self,
        key: Key,
        lsn: Lsn,
@@ -645,7 +644,7 @@ impl DeltaLayerWriterInner {
    ) -> anyhow::Result<()> {
        assert!(self.lsn_range.start <= lsn);

-        let off = self.blob_writer.write_blob(val)?;
+        let off = self.blob_writer.write_blob(val).await?;

        let blob_ref = BlobRef::new(off, will_init);

@@ -662,18 +661,18 @@ impl DeltaLayerWriterInner {
    ///
    /// Finish writing the delta layer.
    ///
-    fn finish(self, key_end: Key) -> anyhow::Result<DeltaLayer> {
+    async fn finish(self, key_end: Key) -> anyhow::Result<DeltaLayer> {
        let index_start_blk =
            ((self.blob_writer.size() + PAGE_SZ as u64 - 1) / PAGE_SZ as u64) as u32;

-        let buf_writer = self.blob_writer.into_inner();
-        let mut file = buf_writer.into_inner()?;
+        let mut file = self.blob_writer.into_inner().await?;

        // Write out the index
        let (index_root_blk, block_buf) = self.tree.finish()?;
-        file.seek(SeekFrom::Start(index_start_blk as u64 * PAGE_SZ as u64))?;
+        file.seek(SeekFrom::Start(index_start_blk as u64 * PAGE_SZ as u64))
+            .await?;
        for buf in block_buf.blocks {
-            file.write_all(buf.as_ref())?;
+            file.write_all(buf.as_ref()).await?;
        }
        assert!(self.lsn_range.start < self.lsn_range.end);
        // Fill in the summary on blk 0
@@ -687,11 +686,22 @@ impl DeltaLayerWriterInner {
            index_start_blk,
            index_root_blk,
        };
-        file.seek(SeekFrom::Start(0))?;
-        Summary::ser_into(&summary, &mut file)?;
+
+        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        Summary::ser_into(&summary, &mut buf)?;
+        if buf.spilled() {
+            // This is bad as we only have one free block for the summary
+            warn!(
+                "Used more than one page size for summary buffer: {}",
+                buf.len()
+            );
+        }
+        file.seek(SeekFrom::Start(0)).await?;
+        file.write_all(&buf).await?;

        let metadata = file
            .metadata()
+            .await
            .context("get file metadata to determine size")?;

        // 5GB limit for objects without multipart upload (which we don't want to use)
@@ -722,7 +732,7 @@ impl DeltaLayerWriterInner {
        };

        // fsync the file
-        file.sync_all()?;
+        file.sync_all().await?;
        // Rename the file to its final name
        //
        // Note: This overwrites any existing file. There shouldn't be any.
@@ -774,7 +784,7 @@ impl DeltaLayerWriter {
    ///
    /// Start building a new delta layer.
    ///
-    pub fn new(
+    pub async fn new(
        conf: &'static PageServerConf,
        timeline_id: TimelineId,
        tenant_id: TenantId,
@@ -782,13 +792,10 @@ impl DeltaLayerWriter {
        lsn_range: Range<Lsn>,
    ) -> anyhow::Result<Self> {
        Ok(Self {
-            inner: Some(DeltaLayerWriterInner::new(
-                conf,
-                timeline_id,
-                tenant_id,
-                key_start,
-                lsn_range,
-            )?),
+            inner: Some(
+                DeltaLayerWriterInner::new(conf, timeline_id, tenant_id, key_start, lsn_range)
+                    .await?,
+            ),
        })
    }

@@ -797,11 +804,11 @@ impl DeltaLayerWriter {
    ///
    /// The values must be appended in key, lsn order.
    ///
-    pub fn put_value(&mut self, key: Key, lsn: Lsn, val: Value) -> anyhow::Result<()> {
-        self.inner.as_mut().unwrap().put_value(key, lsn, val)
+    pub async fn put_value(&mut self, key: Key, lsn: Lsn, val: Value) -> anyhow::Result<()> {
+        self.inner.as_mut().unwrap().put_value(key, lsn, val).await
    }

-    pub fn put_value_bytes(
+    pub async fn put_value_bytes(
        &mut self,
        key: Key,
        lsn: Lsn,
@@ -812,6 +819,7 @@ impl DeltaLayerWriter {
            .as_mut()
            .unwrap()
            .put_value_bytes(key, lsn, val, will_init)
+            .await
    }

    pub fn size(&self) -> u64 {
@@ -821,21 +829,18 @@ impl DeltaLayerWriter {
    ///
    /// Finish writing the delta layer.
    ///
-    pub fn finish(mut self, key_end: Key) -> anyhow::Result<DeltaLayer> {
-        self.inner.take().unwrap().finish(key_end)
+    pub async fn finish(mut self, key_end: Key) -> anyhow::Result<DeltaLayer> {
+        self.inner.take().unwrap().finish(key_end).await
    }
 }

 impl Drop for DeltaLayerWriter {
    fn drop(&mut self) {
        if let Some(inner) = self.inner.take() {
-            match inner.blob_writer.into_inner().into_inner() {
-                Ok(vfile) => vfile.remove(),
-                Err(err) => warn!(
-                    "error while flushing buffer of image layer temporary file: {}",
-                    err
-                ),
-            }
+            // We want to remove the virtual file here, so it's fine to not
+            // having completely flushed unwritten data.
+            let vfile = inner.blob_writer.into_inner_no_flush();
+            vfile.remove();
        }
    }
 }
@@ -844,12 +849,14 @@ impl DeltaLayerInner {
    pub(super) async fn load(
        path: &std::path::Path,
        summary: Option<Summary>,
+        ctx: &RequestContext,
    ) -> anyhow::Result<Self> {
        let file = VirtualFile::open(path)
+            .await
            .with_context(|| format!("Failed to open file '{}'", path.display()))?;
        let file = FileBlockReader::new(file);

-        let summary_blk = file.read_blk(0).await?;
+        let summary_blk = file.read_blk(0, ctx).await?;
        let actual_summary = Summary::des_prefix(summary_blk.as_ref())?;

        if let Some(mut expected_summary) = summary {
@@ -877,6 +884,7 @@ impl DeltaLayerInner {
        key: Key,
        lsn_range: Range<Lsn>,
        reconstruct_state: &mut ValueReconstructState,
+        ctx: &RequestContext,
    ) -> anyhow::Result<ValueReconstructResult> {
        let mut need_image = true;
        // Scan the page versions backwards, starting from `lsn`.
@@ -891,27 +899,38 @@ impl DeltaLayerInner {
        let mut offsets: Vec<(Lsn, u64)> = Vec::new();

        tree_reader
-            .visit(&search_key.0, VisitDirection::Backwards, |key, value| {
-                let blob_ref = BlobRef(value);
-                if key[..KEY_SIZE] != search_key.0[..KEY_SIZE] {
-                    return false;
-                }
-                let entry_lsn = DeltaKey::extract_lsn_from_buf(key);
-                if entry_lsn < lsn_range.start {
-                    return false;
-                }
-                offsets.push((entry_lsn, blob_ref.pos()));
+            .visit(
+                &search_key.0,
+                VisitDirection::Backwards,
+                |key, value| {
+                    let blob_ref = BlobRef(value);
+                    if key[..KEY_SIZE] != search_key.0[..KEY_SIZE] {
+                        return false;
+                    }
+                    let entry_lsn = DeltaKey::extract_lsn_from_buf(key);
+                    if entry_lsn < lsn_range.start {
+                        return false;
+                    }
+                    offsets.push((entry_lsn, blob_ref.pos()));

-                !blob_ref.will_init()
-            })
+                    !blob_ref.will_init()
+                },
+                &RequestContextBuilder::extend(ctx)
+                    .page_content_kind(PageContentKind::DeltaLayerBtreeNode)
+                    .build(),
+            )
            .await?;

+        let ctx = &RequestContextBuilder::extend(ctx)
+            .page_content_kind(PageContentKind::DeltaLayerValue)
+            .build();
+
        // Ok, 'offsets' now contains the offsets of all the entries we need to read
        let cursor = file.block_cursor();
        let mut buf = Vec::new();
        for (entry_lsn, pos) in offsets {
            cursor
-                .read_blob_into_buf(pos, &mut buf)
+                .read_blob_into_buf(pos, &mut buf, ctx)
                .await
                .with_context(|| {
                    format!(
@@ -952,9 +971,10 @@ impl DeltaLayerInner {
        }
    }

-    pub(super) async fn load_keys<T: AsRef<DeltaLayerInner> + Clone>(
-        this: &T,
-    ) -> Result<Vec<DeltaEntry<'_>>> {
+    pub(super) async fn load_keys<'a, 'b, T: AsRef<DeltaLayerInner> + Clone>(
+        this: &'a T,
+        ctx: &'b RequestContext,
+    ) -> Result<Vec<DeltaEntry<'a>>> {
        let dl = this.as_ref();
        let file = &dl.file;

@@ -991,6 +1011,9 @@ impl DeltaLayerInner {
                    all_keys.push(entry);
                    true
                },
+                &RequestContextBuilder::extend(ctx)
+                    .page_content_kind(PageContentKind::DeltaLayerBtreeNode)
+                    .build(),
            )
            .await?;
        if let Some(last) = all_keys.last_mut() {
@@ -1020,9 +1043,9 @@ pub struct ValueRef<'a> {

 impl<'a> ValueRef<'a> {
    /// Loads the value from disk
-    pub async fn load(&self) -> Result<Value> {
+    pub async fn load(&self, ctx: &RequestContext) -> Result<Value> {
        // theoretically we *could* record an access time for each, but it does not really matter
-        let buf = self.reader.read_blob(self.blob_ref.pos()).await?;
+        let buf = self.reader.read_blob(self.blob_ref.pos(), ctx).await?;
        let val = Value::des(&buf)?;
        Ok(val)
    }
@@ -1031,7 +1054,11 @@ impl<'a> ValueRef<'a> {
 pub(crate) struct Adapter<T>(T);

 impl<T: AsRef<DeltaLayerInner>> Adapter<T> {
-    pub(crate) async fn read_blk(&self, blknum: u32) -> Result<BlockLease, std::io::Error> {
-        self.0.as_ref().file.read_blk(blknum).await
+    pub(crate) async fn read_blk(
+        &self,
+        blknum: u32,
+        ctx: &RequestContext,
+    ) -> Result<BlockLease, std::io::Error> {
+        self.0.as_ref().file.read_blk(blknum, ctx).await
    }
 }
--- a/pageserver/src/tenant/storage_layer/filename.rs
+++ b/pageserver/src/tenant/storage_layer/filename.rs
@@ -212,7 +212,7 @@ pub enum LayerFileName {
 }

 impl LayerFileName {
-    pub(crate) fn file_name(&self) -> String {
+    pub fn file_name(&self) -> String {
        self.to_string()
    }

--- a/pageserver/src/tenant/storage_layer/image_layer.rs
+++ b/pageserver/src/tenant/storage_layer/image_layer.rs
@@ -24,10 +24,10 @@
 //! mapping from Key to an offset in the "values" part.  The
 //! actual page images are stored in the "values" part.
 use crate::config::PageServerConf;
-use crate::context::RequestContext;
+use crate::context::{PageContentKind, RequestContext, RequestContextBuilder};
 use crate::page_cache::PAGE_SZ;
 use crate::repository::{Key, KEY_SIZE};
-use crate::tenant::blob_io::{BlobWriter, WriteBlobWriter};
+use crate::tenant::blob_io::BlobWriter;
 use crate::tenant::block_io::{BlockBuf, BlockReader, FileBlockReader};
 use crate::tenant::disk_btree::{DiskBtreeBuilder, DiskBtreeReader, VisitDirection};
 use crate::tenant::storage_layer::{
@@ -42,8 +42,7 @@ use pageserver_api::models::{HistoricLayerInfo, LayerAccessKind};
 use rand::{distributions::Alphanumeric, Rng};
 use serde::{Deserialize, Serialize};
 use std::fs::{self, File};
-use std::io::Write;
-use std::io::{Seek, SeekFrom};
+use std::io::SeekFrom;
 use std::ops::Range;
 use std::os::unix::prelude::FileExt;
 use std::path::{Path, PathBuf};
@@ -155,7 +154,7 @@ pub struct ImageLayerInner {
    lsn: Lsn,

    /// Reader object for reading blocks from the file.
-    file: FileBlockReader<VirtualFile>,
+    file: FileBlockReader,
 }

 impl std::fmt::Debug for ImageLayerInner {
@@ -238,10 +237,15 @@ impl ImageLayer {
        tree_reader.dump().await?;

        tree_reader
-            .visit(&[0u8; KEY_SIZE], VisitDirection::Forwards, |key, value| {
-                println!("key: {} offset {}", hex::encode(key), value);
-                true
-            })
+            .visit(
+                &[0u8; KEY_SIZE],
+                VisitDirection::Forwards,
+                |key, value| {
+                    println!("key: {} offset {}", hex::encode(key), value);
+                    true
+                },
+                ctx,
+            )
            .await?;

        Ok(())
@@ -262,7 +266,7 @@ impl ImageLayer {
            .load(LayerAccessKind::GetValueReconstructData, ctx)
            .await?;
        inner
-            .get_value_reconstruct_data(key, reconstruct_state)
+            .get_value_reconstruct_data(key, reconstruct_state, ctx)
            .await
            // FIXME: makes no sense to dump paths
            .with_context(|| format!("read {}", self.path().display()))
@@ -336,12 +340,12 @@ impl ImageLayer {
    ) -> Result<&ImageLayerInner> {
        self.access_stats.record_access(access_kind, ctx);
        self.inner
-            .get_or_try_init(|| self.load_inner())
+            .get_or_try_init(|| self.load_inner(ctx))
            .await
            .with_context(|| format!("Failed to load image layer {}", self.path().display()))
    }

-    async fn load_inner(&self) -> Result<ImageLayerInner> {
+    async fn load_inner(&self, ctx: &RequestContext) -> Result<ImageLayerInner> {
        let path = self.path();

        let expected_summary = match &self.path_or_conf {
@@ -350,7 +354,8 @@ impl ImageLayer {
        };

        let loaded =
-            ImageLayerInner::load(&path, self.desc.image_layer_lsn(), expected_summary).await?;
+            ImageLayerInner::load(&path, self.desc.image_layer_lsn(), expected_summary, ctx)
+                .await?;

        if let PathOrConf::Path(ref path) = self.path_or_conf {
            // not production code
@@ -437,11 +442,13 @@ impl ImageLayerInner {
        path: &std::path::Path,
        lsn: Lsn,
        summary: Option<Summary>,
+        ctx: &RequestContext,
    ) -> anyhow::Result<Self> {
        let file = VirtualFile::open(path)
+            .await
            .with_context(|| format!("Failed to open file '{}'", path.display()))?;
        let file = FileBlockReader::new(file);
-        let summary_blk = file.read_blk(0).await?;
+        let summary_blk = file.read_blk(0, ctx).await?;
        let actual_summary = Summary::des_prefix(summary_blk.as_ref())?;

        if let Some(mut expected_summary) = summary {
@@ -470,16 +477,30 @@ impl ImageLayerInner {
        &self,
        key: Key,
        reconstruct_state: &mut ValueReconstructState,
+        ctx: &RequestContext,
    ) -> anyhow::Result<ValueReconstructResult> {
        let file = &self.file;
        let tree_reader = DiskBtreeReader::new(self.index_start_blk, self.index_root_blk, file);

        let mut keybuf: [u8; KEY_SIZE] = [0u8; KEY_SIZE];
        key.write_to_byte_slice(&mut keybuf);
-        if let Some(offset) = tree_reader.get(&keybuf).await? {
+        if let Some(offset) = tree_reader
+            .get(
+                &keybuf,
+                &RequestContextBuilder::extend(ctx)
+                    .page_content_kind(PageContentKind::ImageLayerBtreeNode)
+                    .build(),
+            )
+            .await?
+        {
            let blob = file
                .block_cursor()
-                .read_blob(offset)
+                .read_blob(
+                    offset,
+                    &RequestContextBuilder::extend(ctx)
+                        .page_content_kind(PageContentKind::ImageLayerValue)
+                        .build(),
+                )
                .await
                .with_context(|| format!("failed to read value from offset {}", offset))?;
            let value = Bytes::from(blob);
@@ -511,7 +532,7 @@ struct ImageLayerWriterInner {
    key_range: Range<Key>,
    lsn: Lsn,

-    blob_writer: WriteBlobWriter<VirtualFile>,
+    blob_writer: BlobWriter<false>,
    tree: DiskBtreeBuilder<BlockBuf, KEY_SIZE>,
 }

@@ -519,7 +540,7 @@ impl ImageLayerWriterInner {
    ///
    /// Start building a new image layer.
    ///
-    fn new(
+    async fn new(
        conf: &'static PageServerConf,
        timeline_id: TimelineId,
        tenant_id: TenantId,
@@ -541,10 +562,11 @@ impl ImageLayerWriterInner {
        let mut file = VirtualFile::open_with_options(
            &path,
            std::fs::OpenOptions::new().write(true).create_new(true),
-        )?;
+        )
+        .await?;
        // make room for the header block
-        file.seek(SeekFrom::Start(PAGE_SZ as u64))?;
-        let blob_writer = WriteBlobWriter::new(file, PAGE_SZ as u64);
+        file.seek(SeekFrom::Start(PAGE_SZ as u64)).await?;
+        let blob_writer = BlobWriter::new(file, PAGE_SZ as u64);

        // Initialize the b-tree index builder
        let block_buf = BlockBuf::new();
@@ -569,9 +591,9 @@ impl ImageLayerWriterInner {
    ///
    /// The page versions must be appended in blknum order.
    ///
-    fn put_image(&mut self, key: Key, img: &[u8]) -> anyhow::Result<()> {
+    async fn put_image(&mut self, key: Key, img: &[u8]) -> anyhow::Result<()> {
        ensure!(self.key_range.contains(&key));
-        let off = self.blob_writer.write_blob(img)?;
+        let off = self.blob_writer.write_blob(img).await?;

        let mut keybuf: [u8; KEY_SIZE] = [0u8; KEY_SIZE];
        key.write_to_byte_slice(&mut keybuf);
@@ -583,17 +605,18 @@ impl ImageLayerWriterInner {
    ///
    /// Finish writing the image layer.
    ///
-    fn finish(self) -> anyhow::Result<ImageLayer> {
+    async fn finish(self) -> anyhow::Result<ImageLayer> {
        let index_start_blk =
            ((self.blob_writer.size() + PAGE_SZ as u64 - 1) / PAGE_SZ as u64) as u32;

        let mut file = self.blob_writer.into_inner();

        // Write out the index
-        file.seek(SeekFrom::Start(index_start_blk as u64 * PAGE_SZ as u64))?;
+        file.seek(SeekFrom::Start(index_start_blk as u64 * PAGE_SZ as u64))
+            .await?;
        let (index_root_blk, block_buf) = self.tree.finish()?;
        for buf in block_buf.blocks {
-            file.write_all(buf.as_ref())?;
+            file.write_all(buf.as_ref()).await?;
        }

        // Fill in the summary on blk 0
@@ -607,11 +630,22 @@ impl ImageLayerWriterInner {
            index_start_blk,
            index_root_blk,
        };
-        file.seek(SeekFrom::Start(0))?;
-        Summary::ser_into(&summary, &mut file)?;
+
+        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        Summary::ser_into(&summary, &mut buf)?;
+        if buf.spilled() {
+            // This is bad as we only have one free block for the summary
+            warn!(
+                "Used more than one page size for summary buffer: {}",
+                buf.len()
+            );
+        }
+        file.seek(SeekFrom::Start(0)).await?;
+        file.write_all(&buf).await?;

        let metadata = file
            .metadata()
+            .await
            .context("get metadata to determine file size")?;

        let desc = PersistentLayerDesc::new_img(
@@ -634,7 +668,7 @@ impl ImageLayerWriterInner {
        };

        // fsync the file
-        file.sync_all()?;
+        file.sync_all().await?;

        // Rename the file to its final name
        //
@@ -687,7 +721,7 @@ impl ImageLayerWriter {
    ///
    /// Start building a new image layer.
    ///
-    pub fn new(
+    pub async fn new(
        conf: &'static PageServerConf,
        timeline_id: TimelineId,
        tenant_id: TenantId,
@@ -695,13 +729,9 @@ impl ImageLayerWriter {
        lsn: Lsn,
    ) -> anyhow::Result<ImageLayerWriter> {
        Ok(Self {
-            inner: Some(ImageLayerWriterInner::new(
-                conf,
-                timeline_id,
-                tenant_id,
-                key_range,
-                lsn,
-            )?),
+            inner: Some(
+                ImageLayerWriterInner::new(conf, timeline_id, tenant_id, key_range, lsn).await?,
+            ),
        })
    }

@@ -710,15 +740,15 @@ impl ImageLayerWriter {
    ///
    /// The page versions must be appended in blknum order.
    ///
-    pub fn put_image(&mut self, key: Key, img: &[u8]) -> anyhow::Result<()> {
-        self.inner.as_mut().unwrap().put_image(key, img)
+    pub async fn put_image(&mut self, key: Key, img: &[u8]) -> anyhow::Result<()> {
+        self.inner.as_mut().unwrap().put_image(key, img).await
    }

    ///
    /// Finish writing the image layer.
    ///
-    pub fn finish(mut self) -> anyhow::Result<ImageLayer> {
-        self.inner.take().unwrap().finish()
+    pub async fn finish(mut self) -> anyhow::Result<ImageLayer> {
+        self.inner.take().unwrap().finish().await
    }
 }

--- a/Show More
+++ b/Show More