Fix LSN lease background thread with grpc

The spawned thread didn't have the tokio runtime active, which lead to
this error:

    ERROR lsn_lease_bg_task{tenant_id=1bb647cb7d3974b52e74f7442fa7d059 timeline_id=cf41456d3202e1c3940cb8f372d160ab lsn=0/1576000}:panic{thread=<unnamed> location=compute_tools/src/lsn_lease.rs:201:5}: there is no reactor running, must be called from the context of a Tokio 1.x runtime

Fixes `test_readonly_node_gc`

.gitignore

@@ -15,6 +15,7 @@ neon.iml
 /.neon
 /integration_tests/.neon
 compaction-suite-results.*
+pgxn/neon/communicator/communicator_bindings.h
 docker-compose/docker-compose-parallel.yml
 
 # Coverage

Cargo.lock

@@ -259,6 +259,17 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a8ab6b55fe97976e46f91ddbed8d147d966475dc29b2032757ba47e02376fbc3"
 
+[[package]]
+name = "atomic_enum"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "99e1aca718ea7b89985790c94aad72d77533063fe00bc497bb79a7c2dae6a661"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.100",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.1.0"
@@ -1296,13 +1307,29 @@ dependencies = [
 name = "communicator"
 version = "0.1.0"
 dependencies = [
+ "atomic_enum",
  "axum",
+ "bytes",
  "cbindgen",
+ "clashmap",
  "http 1.3.1",
+ "libc",
  "measured",
+ "neon-shmem",
+ "nix 0.30.1",
+ "pageserver_api",
+ "pageserver_client_grpc",
+ "pageserver_page_api",
+ "prometheus",
+ "prost 0.13.5",
+ "strum_macros",
+ "thiserror 1.0.69",
  "tokio",
+ "tokio-pipe",
+ "tonic",
  "tracing",
  "tracing-subscriber",
+ "uring-common",
  "utils",
  "workspace_hack",
 ]
@@ -1643,9 +1670,9 @@ dependencies = [
 
 [[package]]
 name = "crossbeam-utils"
-version = "0.8.19"
+version = "0.8.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "248e3bacc7dc6baa3b21e405ee045c3047101a49145e7e9eca583ab4c2ca5345"
+checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
 
 [[package]]
 name = "crossterm"
@@ -2361,6 +2388,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "form_urlencoded"
 version = "1.2.1"
@@ -2742,6 +2775,16 @@ version = "0.15.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bf151400ff0baff5465007dd2f3e717f3fe502074ca563069ce3a6629d07b289"
 
+[[package]]
+name = "hashbrown"
+version = "0.15.4"
+source = "git+https://github.com/quantumish/hashbrown.git?rev=6610e6d#6610e6d2b1f288ef7b0709a3efefbc846395dc5e"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash",
+]
+
 [[package]]
 name = "hashlink"
 version = "0.9.1"
@@ -3822,7 +3865,7 @@ dependencies = [
  "prometheus",
  "rand 0.9.1",
  "rand_distr",
- "twox-hash",
+ "twox-hash 1.6.3",
 ]
 
 [[package]]
@@ -3928,15 +3971,21 @@ checksum = "e5ce46fe64a9d73be07dcbe690a38ce1b293be448fd8ce1e6c1b8062c9f72c6a"
 name = "neon-shmem"
 version = "0.1.0"
 dependencies = [
+ "ahash",
+ "criterion",
+ "hashbrown 0.15.4",
  "libc",
  "lock_api",
  "nix 0.30.1",
  "rand 0.9.1",
  "rand_distr",
  "rustc-hash 2.1.1",
+ "seahash",
  "tempfile",
  "thiserror 1.0.69",
+ "twox-hash 2.1.1",
  "workspace_hack",
+ "xxhash-rust",
 ]
 
 [[package]]
@@ -4391,13 +4440,16 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "async-trait",
+ "axum",
  "bytes",
  "camino",
  "clap",
  "futures",
  "hdrhistogram",
+ "http 1.3.1",
  "humantime",
  "humantime-serde",
+ "metrics",
  "pageserver_api",
  "pageserver_client",
  "pageserver_client_grpc",
@@ -4487,6 +4539,7 @@ dependencies = [
  "pageserver_client",
  "pageserver_compaction",
  "pageserver_page_api",
+ "peekable",
  "pem",
  "pin-project-lite",
  "postgres-protocol",
@@ -4500,6 +4553,7 @@ dependencies = [
  "pprof",
  "pq_proto",
  "procfs",
+ "prost 0.13.5",
  "rand 0.9.1",
  "range-set-blaze",
  "regex",
@@ -4536,7 +4590,7 @@ dependencies = [
  "tower 0.5.2",
  "tracing",
  "tracing-utils",
- "twox-hash",
+ "twox-hash 1.6.3",
  "url",
  "utils",
  "uuid",
@@ -4748,7 +4802,7 @@ dependencies = [
  "paste",
  "seq-macro",
  "thrift",
- "twox-hash",
+ "twox-hash 1.6.3",
  "zstd",
  "zstd-sys",
 ]
@@ -4794,6 +4848,15 @@ dependencies = [
  "sha2",
 ]
 
+[[package]]
+name = "peekable"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "225f9651e475709164f871dc2f5724956be59cb9edb055372ffeeab01ec2d20b"
+dependencies = [
+ "smallvec",
+]
+
 [[package]]
 name = "pem"
 version = "3.0.3"
@@ -6493,6 +6556,12 @@ version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "621e3680f3e07db4c9c2c3fb07c6223ab2fab2e54bd3c04c3ae037990f428c32"
 
+[[package]]
+name = "seahash"
+version = "4.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
+
 [[package]]
 name = "sec1"
 version = "0.3.0"
@@ -7646,6 +7715,16 @@ dependencies = [
  "syn 2.0.100",
 ]
 
+[[package]]
+name = "tokio-pipe"
+version = "0.2.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f213a84bffbd61b8fa0ba8a044b4bbe35d471d0b518867181e82bd5c15542784"
+dependencies = [
+ "libc",
+ "tokio",
+]
+
 [[package]]
 name = "tokio-postgres"
 version = "0.7.10"
@@ -8183,6 +8262,15 @@ dependencies = [
  "static_assertions",
 ]
 
+[[package]]
+name = "twox-hash"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b907da542cbced5261bd3256de1b3a1bf340a3d37f93425a07362a1d687de56"
+dependencies = [
+ "rand 0.9.1",
+]
+
 [[package]]
 name = "typed-json"
 version = "0.1.1"
@@ -9013,8 +9101,8 @@ dependencies = [
  "clap",
  "clap_builder",
  "const-oid",
+ "criterion",
  "crossbeam-epoch",
- "crossbeam-utils",
  "crypto-bigint 0.5.5",
  "der 0.7.8",
  "deranged",
@@ -9057,7 +9145,6 @@ dependencies = [
  "num-iter",
  "num-rational",
  "num-traits",
- "once_cell",
  "p256 0.13.2",
  "parquet",
  "portable-atomic",
@@ -9166,6 +9253,12 @@ version = "0.13.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4d25c75bf9ea12c4040a97f829154768bbbce366287e2dc044af160cd79a13fd"
 
+[[package]]
+name = "xxhash-rust"
+version = "0.8.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fdd20c5420375476fbd4394763288da7eb0cc0b8c11deed431a91562af7335d3"
+
 [[package]]
 name = "yansi"
 version = "1.0.1"

Cargo.toml

@@ -93,6 +93,7 @@ clap = { version = "4.0", features = ["derive", "env"] }
 clashmap = { version = "1.0", features = ["raw-api"] }
 comfy-table = "7.1"
 const_format = "0.2"
+crossbeam-utils = "0.8.21"
 crc32c = "0.6"
 diatomic-waker = { version = "0.2.3" }
 either = "1.8"
@@ -152,6 +153,7 @@ parquet = { version = "53", default-features = false, features = ["zstd"] }
 parquet_derive = "53"
 pbkdf2 = { version = "0.12.1", features = ["simple", "std"] }
 pem = "3.0.3"
+peekable = "0.3.0"
 pin-project-lite = "0.2"
 pprof = { version = "0.14", features = ["criterion", "flamegraph", "frame-pointer", "prost-codec"] }
 procfs = "0.16"
@@ -190,6 +192,7 @@ smallvec = "1.11"
 smol_str = { version = "0.2.0", features = ["serde"] }
 socket2 = "0.5"
 spki = "0.7.3"
+spin = "0.9.8"
 strum = "0.26"
 strum_macros = "0.26"
 "subtle"  = "2.5.0"
@@ -201,7 +204,6 @@ thiserror = "1.0"
 tikv-jemallocator = { version = "0.6", features = ["profiling", "stats", "unprefixed_malloc_on_supported_platforms"] }
 tikv-jemalloc-ctl = { version = "0.6", features = ["stats"] }
 tokio = { version = "1.43.1", features = ["macros"] }
-tokio-epoll-uring = { git = "https://github.com/neondatabase/tokio-epoll-uring.git" , branch = "main" }
 tokio-io-timeout = "1.2.0"
 tokio-postgres-rustls = "0.12.0"
 tokio-rustls = { version = "0.26.0", default-features = false, features = ["tls12", "ring"]}
@@ -242,6 +244,9 @@ zeroize = "1.8"
 env_logger = "0.11"
 log = "0.4"
 
+tokio-epoll-uring = { git = "https://github.com/neondatabase/tokio-epoll-uring.git" , branch = "main" }
+uring-common = { git = "https://github.com/neondatabase/tokio-epoll-uring.git" , branch = "main" }
+
 ## Libraries from neondatabase/ git forks, ideally with changes to be upstreamed
 postgres = { git = "https://github.com/neondatabase/rust-postgres.git", branch = "neon" }
 postgres-protocol = { git = "https://github.com/neondatabase/rust-postgres.git", branch = "neon" }

compute/etc/sql_exporter/checkpoints_req.17.sql

@@ -1 +1 @@
-SELECT num_requested AS checkpoints_req FROM pg_stat_checkpointer;
+SELECT num_requested AS checkpoints_req FROM pg_catalog.pg_stat_checkpointer;

compute/etc/sql_exporter/checkpoints_req.sql

@@ -1 +1 @@
-SELECT checkpoints_req FROM pg_stat_bgwriter;
+SELECT checkpoints_req FROM pg_catalog.pg_stat_bgwriter;

compute/etc/sql_exporter/checkpoints_timed.sql

@@ -1 +1 @@
-SELECT checkpoints_timed FROM pg_stat_bgwriter;
+SELECT checkpoints_timed FROM pg_catalog.pg_stat_bgwriter;

compute/etc/sql_exporter/compute_backpressure_throttling_seconds_total.sql

@@ -1 +1 @@
-SELECT (neon.backpressure_throttling_time()::float8 / 1000000) AS throttled;
+SELECT (neon.backpressure_throttling_time()::pg_catalog.float8 / 1000000) AS throttled;

compute/etc/sql_exporter/compute_current_lsn.sql

@@ -1,4 +1,4 @@
 SELECT CASE
-  WHEN pg_catalog.pg_is_in_recovery() THEN (pg_last_wal_replay_lsn() - '0/0')::FLOAT8
+  WHEN pg_catalog.pg_is_in_recovery() THEN (pg_catalog.pg_last_wal_replay_lsn() - '0/0')::pg_catalog.FLOAT8
-  ELSE (pg_current_wal_lsn() - '0/0')::FLOAT8
+  ELSE (pg_catalog.pg_current_wal_lsn() - '0/0')::pg_catalog.FLOAT8
 END AS lsn;

compute/etc/sql_exporter/compute_logical_snapshot_files.sql

@@ -1,7 +1,7 @@
 SELECT
-  (SELECT setting FROM pg_settings WHERE name = 'neon.timeline_id') AS timeline_id,
+  (SELECT setting FROM pg_catalog.pg_settings WHERE name = 'neon.timeline_id') AS timeline_id,
   -- Postgres creates temporary snapshot files of the form %X-%X.snap.%d.tmp.
   -- These temporary snapshot files are renamed to the actual snapshot files
   -- after they are completely built. We only WAL-log the completely built
   -- snapshot files
-  (SELECT COUNT(*) FROM pg_ls_dir('pg_logical/snapshots') AS name WHERE name LIKE '%.snap') AS num_logical_snapshot_files;
+  (SELECT COUNT(*) FROM pg_catalog.pg_ls_dir('pg_logical/snapshots') AS name WHERE name LIKE '%.snap') AS num_logical_snapshot_files;

compute/etc/sql_exporter/compute_logical_snapshots_bytes.15.sql

@@ -1,7 +1,7 @@
 SELECT
-  (SELECT current_setting('neon.timeline_id')) AS timeline_id,
+  (SELECT pg_catalog.current_setting('neon.timeline_id')) AS timeline_id,
   -- Postgres creates temporary snapshot files of the form %X-%X.snap.%d.tmp.
   -- These temporary snapshot files are renamed to the actual snapshot files
   -- after they are completely built. We only WAL-log the completely built
   -- snapshot files
-  (SELECT COALESCE(sum(size), 0) FROM pg_ls_logicalsnapdir() WHERE name LIKE '%.snap') AS logical_snapshots_bytes;
+  (SELECT COALESCE(pg_catalog.sum(size), 0) FROM pg_catalog.pg_ls_logicalsnapdir() WHERE name LIKE '%.snap') AS logical_snapshots_bytes;

compute/etc/sql_exporter/compute_logical_snapshots_bytes.sql

@@ -1,9 +1,9 @@
 SELECT
-  (SELECT setting FROM pg_settings WHERE name = 'neon.timeline_id') AS timeline_id,
+  (SELECT setting FROM pg_catalog.pg_settings WHERE name = 'neon.timeline_id') AS timeline_id,
   -- Postgres creates temporary snapshot files of the form %X-%X.snap.%d.tmp.
   -- These temporary snapshot files are renamed to the actual snapshot files
   -- after they are completely built. We only WAL-log the completely built
   -- snapshot files
-  (SELECT COALESCE(sum((pg_stat_file('pg_logical/snapshots/' || name, missing_ok => true)).size), 0)
+  (SELECT COALESCE(pg_catalog.sum((pg_catalog.pg_stat_file('pg_logical/snapshots/' || name, missing_ok => true)).size), 0)
-    FROM (SELECT * FROM pg_ls_dir('pg_logical/snapshots') WHERE pg_ls_dir LIKE '%.snap') AS name
+   FROM (SELECT * FROM pg_catalog.pg_ls_dir('pg_logical/snapshots') WHERE pg_ls_dir LIKE '%.snap') AS name
   ) AS logical_snapshots_bytes;

compute/etc/sql_exporter/compute_max_connections.sql

@@ -1 +1 @@
-SELECT current_setting('max_connections') as max_connections;
+SELECT pg_catalog.current_setting('max_connections') AS max_connections;

compute/etc/sql_exporter/compute_pg_oldest_frozen_xid_age.sql

@@ -1,4 +1,4 @@
 SELECT datname database_name,
-  age(datfrozenxid) frozen_xid_age
+   pg_catalog.age(datfrozenxid) frozen_xid_age
-FROM pg_database
+FROM pg_catalog.pg_database
 ORDER BY frozen_xid_age DESC LIMIT 10;

compute/etc/sql_exporter/compute_pg_oldest_mxid_age.sql

@@ -1,4 +1,4 @@
 SELECT datname database_name,
-  mxid_age(datminmxid) min_mxid_age
+  pg_catalog.mxid_age(datminmxid) min_mxid_age
-FROM pg_database
+FROM pg_catalog.pg_database
 ORDER BY min_mxid_age DESC LIMIT 10;

compute/etc/sql_exporter/compute_receive_lsn.sql

@@ -1,4 +1,4 @@
 SELECT CASE
-  WHEN pg_catalog.pg_is_in_recovery() THEN (pg_last_wal_receive_lsn() - '0/0')::FLOAT8
+  WHEN pg_catalog.pg_is_in_recovery() THEN (pg_catalog.pg_last_wal_receive_lsn() - '0/0')::pg_catalog.FLOAT8
   ELSE 0
 END AS lsn;

compute/etc/sql_exporter/compute_subscriptions_count.sql

@@ -1 +1 @@
-SELECT subenabled::text AS enabled, count(*) AS subscriptions_count FROM pg_subscription GROUP BY subenabled;
+SELECT subenabled::pg_catalog.text AS enabled, pg_catalog.count(*) AS subscriptions_count FROM pg_catalog.pg_subscription GROUP BY subenabled;

compute/etc/sql_exporter/connection_counts.sql

@@ -1 +1 @@
-SELECT datname, state, count(*) AS count FROM pg_stat_activity WHERE state <> '' GROUP BY datname, state;
+SELECT datname, state, pg_catalog.count(*) AS count FROM pg_catalog.pg_stat_activity WHERE state <> '' GROUP BY datname, state;

compute/etc/sql_exporter/db_total_size.sql

@@ -1,5 +1,5 @@
-SELECT sum(pg_database_size(datname)) AS total
+SELECT pg_catalog.sum(pg_catalog.pg_database_size(datname)) AS total
-FROM pg_database
+FROM pg_catalog.pg_database
 -- Ignore invalid databases, as we will likely have problems with
 -- getting their size from the Pageserver.
 WHERE datconnlimit != -2;

compute/etc/sql_exporter/lfc_approximate_working_set_size_windows.autoscaling.sql

@@ -3,6 +3,6 @@
 -- minutes.
 
 SELECT
-  x::text as duration_seconds,
+  x::pg_catalog.text AS duration_seconds,
   neon.approximate_working_set_size_seconds(x) AS size
 FROM (SELECT generate_series * 60 AS x FROM generate_series(1, 60)) AS t (x);

compute/etc/sql_exporter/lfc_approximate_working_set_size_windows.sql

@@ -3,6 +3,6 @@
 
 SELECT
   x AS duration,
-  neon.approximate_working_set_size_seconds(extract('epoch' FROM x::interval)::int) AS size FROM (
+  neon.approximate_working_set_size_seconds(extract('epoch' FROM x::pg_catalog.interval)::pg_catalog.int4) AS size FROM (
     VALUES ('5m'), ('15m'), ('1h')
   ) AS t (x);

compute/etc/sql_exporter/lfc_cache_size_limit.sql

@@ -1 +1 @@
-SELECT pg_size_bytes(current_setting('neon.file_cache_size_limit')) AS lfc_cache_size_limit;
+SELECT pg_catalog.pg_size_bytes(pg_catalog.current_setting('neon.file_cache_size_limit')) AS lfc_cache_size_limit;

compute/etc/sql_exporter/logical_slot_restart_lsn.sql

@@ -1,3 +1,3 @@
-SELECT slot_name, (restart_lsn - '0/0')::FLOAT8 as restart_lsn
+SELECT slot_name, (restart_lsn - '0/0')::pg_catalog.FLOAT8 AS restart_lsn
-FROM pg_replication_slots
+FROM pg_catalog.pg_replication_slots
 WHERE slot_type = 'logical';

compute/etc/sql_exporter/max_cluster_size.sql

@@ -1 +1 @@
-SELECT setting::int AS max_cluster_size FROM pg_settings WHERE name = 'neon.max_cluster_size';
+SELECT setting::pg_catalog.int4 AS max_cluster_size FROM pg_catalog.pg_settings WHERE name = 'neon.max_cluster_size';

compute/etc/sql_exporter/pg_stats_userdb.sql

@@ -1,13 +1,13 @@
 -- We export stats for 10 non-system databases. Without this limit it is too
 -- easy to abuse the system by creating lots of databases.
 
-SELECT pg_database_size(datname) AS db_size,
+SELECT pg_catalog.pg_database_size(datname) AS db_size,
   deadlocks,
   tup_inserted AS inserted,
   tup_updated AS updated,
   tup_deleted AS deleted,
   datname
-FROM pg_stat_database
+FROM pg_catalog.pg_stat_database
 WHERE datname IN (
   SELECT datname FROM pg_database
   -- Ignore invalid databases, as we will likely have problems with

compute/etc/sql_exporter/replication_delay_bytes.sql

@@ -3,4 +3,4 @@
 -- replay LSN may have advanced past the receive LSN we are using for the
 -- calculation.
 
-SELECT GREATEST(0, pg_wal_lsn_diff(pg_last_wal_receive_lsn(), pg_last_wal_replay_lsn())) AS replication_delay_bytes;
+SELECT GREATEST(0, pg_catalog.pg_wal_lsn_diff(pg_catalog.pg_last_wal_receive_lsn(), pg_catalog.pg_last_wal_replay_lsn())) AS replication_delay_bytes;

compute/etc/sql_exporter/replication_delay_seconds.sql

@@ -1,5 +1,5 @@
 SELECT
   CASE
-    WHEN pg_last_wal_receive_lsn() = pg_last_wal_replay_lsn() THEN 0
+    WHEN pg_catalog.pg_last_wal_receive_lsn() = pg_catalog.pg_last_wal_replay_lsn() THEN 0
-    ELSE GREATEST(0, EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp()))
+    ELSE GREATEST(0, EXTRACT (EPOCH FROM pg_catalog.now() - pg_catalog.pg_last_xact_replay_timestamp()))
   END AS replication_delay_seconds;

compute/etc/sql_exporter/retained_wal.sql

@@ -1,10 +1,10 @@
 SELECT
   slot_name,
-  pg_wal_lsn_diff(
+  pg_catalog.pg_wal_lsn_diff(
     CASE
-      WHEN pg_is_in_recovery() THEN pg_last_wal_replay_lsn()
+      WHEN pg_catalog.pg_is_in_recovery() THEN pg_catalog.pg_last_wal_replay_lsn()
-      ELSE pg_current_wal_lsn()
+      ELSE pg_catalog.pg_current_wal_lsn()
     END,
-    restart_lsn)::FLOAT8 AS retained_wal
+    restart_lsn)::pg_catalog.FLOAT8 AS retained_wal
-FROM pg_replication_slots
+FROM pg_catalog.pg_replication_slots
 WHERE active = false;

compute/etc/sql_exporter/wal_is_lost.sql

@@ -4,4 +4,4 @@ SELECT
     WHEN wal_status = 'lost' THEN 1
     ELSE 0
   END AS wal_is_lost
-FROM pg_replication_slots;
+FROM pg_catalog.pg_replication_slots;

compute_tools/src/bin/compute_ctl.rs

@@ -279,7 +279,7 @@ fn main() -> Result<()> {
         config,
     )?;
 
-    let exit_code = compute_node.run()?;
+    let exit_code = compute_node.run().context("running compute node")?;
 
     scenario.teardown();
 

compute_tools/src/checker.rs

@@ -24,9 +24,9 @@ pub async fn check_writability(compute: &ComputeNode) -> Result<()> {
     });
 
     let query = "
-    INSERT INTO health_check VALUES (1, now())
+    INSERT INTO public.health_check VALUES (1, pg_catalog.now())
         ON CONFLICT (id) DO UPDATE
-         SET updated_at = now();";
+         SET updated_at = pg_catalog.now();";
 
     match client.simple_query(query).await {
         Result::Ok(result) => {

compute_tools/src/compute.rs

@@ -32,8 +32,12 @@ use std::sync::{Arc, Condvar, Mutex, RwLock};
 use std::time::{Duration, Instant};
 use std::{env, fs};
 use tokio::{spawn, sync::watch, task::JoinHandle, time};
+use tokio_util::sync::CancellationToken;
 use tracing::{Instrument, debug, error, info, instrument, warn};
 use url::Url;
+use utils::backoff::{
+    DEFAULT_BASE_BACKOFF_SECONDS, DEFAULT_MAX_BACKOFF_SECONDS, exponential_backoff_duration,
+};
 use utils::id::{TenantId, TimelineId};
 use utils::lsn::Lsn;
 use utils::measured_stream::MeasuredReader;
@@ -192,6 +196,7 @@ pub struct ComputeState {
     pub startup_span: Option<tracing::span::Span>,
 
     pub lfc_prewarm_state: LfcPrewarmState,
+    pub lfc_prewarm_token: CancellationToken,
     pub lfc_offload_state: LfcOffloadState,
 
     /// WAL flush LSN that is set after terminating Postgres and syncing safekeepers if
@@ -217,6 +222,7 @@ impl ComputeState {
             lfc_offload_state: LfcOffloadState::default(),
             terminate_flush_lsn: None,
             promote_state: None,
+            lfc_prewarm_token: CancellationToken::new(),
         }
     }
 
@@ -583,7 +589,7 @@ impl ComputeNode {
         // that can affect `compute_ctl` and prevent it from properly configuring the database schema.
         // Unset them via connection string options before connecting to the database.
         // N.B. keep it in sync with `ZENITH_OPTIONS` in `get_maintenance_client()`.
-        const EXTRA_OPTIONS: &str = "-c role=cloud_admin -c default_transaction_read_only=off -c search_path=public -c statement_timeout=0 -c pgaudit.log=none";
+        const EXTRA_OPTIONS: &str = "-c role=cloud_admin -c default_transaction_read_only=off -c search_path='' -c statement_timeout=0 -c pgaudit.log=none";
         let options = match conn_conf.get_options() {
             // Allow the control plane to override any options set by the
             // compute
@@ -1554,6 +1560,41 @@ impl ComputeNode {
         Ok(lsn)
     }
 
+    fn sync_safekeepers_with_retries(&self, storage_auth_token: Option<String>) -> Result<Lsn> {
+        let max_retries = 5;
+        let mut attempts = 0;
+        loop {
+            let result = self.sync_safekeepers(storage_auth_token.clone());
+            match &result {
+                Ok(_) => {
+                    if attempts > 0 {
+                        tracing::info!("sync_safekeepers succeeded after {attempts} retries");
+                    }
+                    return result;
+                }
+                Err(e) if attempts < max_retries => {
+                    tracing::info!(
+                        "sync_safekeepers failed, will retry (attempt {attempts}): {e:#}"
+                    );
+                }
+                Err(err) => {
+                    tracing::warn!(
+                        "sync_safekeepers still failed after {attempts} retries, giving up: {err:?}"
+                    );
+                    return result;
+                }
+            }
+            // sleep and retry
+            let backoff = exponential_backoff_duration(
+                attempts,
+                DEFAULT_BASE_BACKOFF_SECONDS,
+                DEFAULT_MAX_BACKOFF_SECONDS,
+            );
+            std::thread::sleep(backoff);
+            attempts += 1;
+        }
+    }
+
     /// Do all the preparations like PGDATA directory creation, configuration,
     /// safekeepers sync, basebackup, etc.
     #[instrument(skip_all)]
@@ -1589,7 +1630,7 @@ impl ComputeNode {
                     lsn
                 } else {
                     info!("starting safekeepers syncing");
-                    self.sync_safekeepers(pspec.storage_auth_token.clone())
+                    self.sync_safekeepers_with_retries(pspec.storage_auth_token.clone())
                         .with_context(|| "failed to sync safekeepers")?
                 };
                 info!("safekeepers synced at LSN {}", lsn);
@@ -1884,7 +1925,7 @@ impl ComputeNode {
 
                     // It doesn't matter what were the options before, here we just want
                     // to connect and create a new superuser role.
-                    const ZENITH_OPTIONS: &str = "-c role=zenith_admin -c default_transaction_read_only=off -c search_path=public -c statement_timeout=0";
+                    const ZENITH_OPTIONS: &str = "-c role=zenith_admin -c default_transaction_read_only=off -c search_path='' -c statement_timeout=0";
                     zenith_admin_conf.options(ZENITH_OPTIONS);
 
                     let mut client =
@@ -2339,13 +2380,13 @@ impl ComputeNode {
         let result = client
             .simple_query(
                 "SELECT
-    row_to_json(pg_stat_statements)
+    pg_catalog.row_to_json(pss)
 FROM
-    pg_stat_statements
+    public.pg_stat_statements pss
 WHERE
-    userid != 'cloud_admin'::regrole::oid
+    pss.userid != 'cloud_admin'::pg_catalog.regrole::pg_catalog.oid
 ORDER BY
-    (mean_exec_time + mean_plan_time) DESC
+    (pss.mean_exec_time + pss.mean_plan_time) DESC
 LIMIT 100",
             )
             .await;
@@ -2473,11 +2514,11 @@ LIMIT 100",
 
         // check the role grants first - to gracefully handle read-replicas.
         let select = "SELECT privilege_type
-            FROM pg_namespace
+            FROM pg_catalog.pg_namespace
-                JOIN LATERAL (SELECT * FROM aclexplode(nspacl) AS x) acl ON true
+                JOIN LATERAL (SELECT * FROM aclexplode(nspacl) AS x) AS acl ON true
-                JOIN pg_user users ON acl.grantee = users.usesysid
+                JOIN pg_catalog.pg_user users ON acl.grantee = users.usesysid
-            WHERE users.usename = $1
+            WHERE users.usename OPERATOR(pg_catalog.=) $1::pg_catalog.name
-                AND nspname = $2";
+                AND nspname OPERATOR(pg_catalog.=) $2::pg_catalog.name";
         let rows = db_client
             .query(select, &[role_name, schema_name])
             .await
@@ -2546,8 +2587,9 @@ LIMIT 100",
                 .await
                 .with_context(|| format!("Failed to execute query: {query}"))?;
         } else {
-            let query =
+            let query = format!(
-                format!("CREATE EXTENSION IF NOT EXISTS {ext_name} WITH VERSION {quoted_version}");
+                "CREATE EXTENSION IF NOT EXISTS {ext_name} WITH SCHEMA public VERSION {quoted_version}"
+            );
             db_client
                 .simple_query(&query)
                 .await

compute_tools/src/compute_prewarm.rs

@@ -7,7 +7,8 @@ use http::StatusCode;
 use reqwest::Client;
 use std::mem::replace;
 use std::sync::Arc;
-use tokio::{io::AsyncReadExt, spawn};
+use tokio::{io::AsyncReadExt, select, spawn};
+use tokio_util::sync::CancellationToken;
 use tracing::{error, info};
 
 #[derive(serde::Serialize, Default)]
@@ -92,34 +93,35 @@ impl ComputeNode {
     /// If there is a prewarm request ongoing, return `false`, `true` otherwise.
     /// Has a failpoint "compute-prewarm"
     pub fn prewarm_lfc(self: &Arc<Self>, from_endpoint: Option<String>) -> bool {
+        let token: CancellationToken;
         {
-            let state = &mut self.state.lock().unwrap().lfc_prewarm_state;
+            let state = &mut self.state.lock().unwrap();
-            if let LfcPrewarmState::Prewarming = replace(state, LfcPrewarmState::Prewarming) {
+            token = state.lfc_prewarm_token.clone();
+            if let LfcPrewarmState::Prewarming =
+                replace(&mut state.lfc_prewarm_state, LfcPrewarmState::Prewarming)
+            {
                 return false;
             }
         }
         crate::metrics::LFC_PREWARMS.inc();
 
-        let cloned = self.clone();
+        let this = self.clone();
         spawn(async move {
-            let state = match cloned.prewarm_impl(from_endpoint).await {
+            let prewarm_state = match this.prewarm_impl(from_endpoint, token).await {
-                Ok(true) => LfcPrewarmState::Completed,
+                Ok(state) => state,
-                Ok(false) => {
-                    info!(
-                        "skipping LFC prewarm because LFC state is not found in endpoint storage"
-                    );
-                    LfcPrewarmState::Skipped
-                }
                 Err(err) => {
                     crate::metrics::LFC_PREWARM_ERRORS.inc();
                     error!(%err, "could not prewarm LFC");
-                    LfcPrewarmState::Failed {
+                    let error = format!("{err:#}");
-                        error: format!("{err:#}"),
+                    LfcPrewarmState::Failed { error }
-                    }
                 }
             };
 
-            cloned.state.lock().unwrap().lfc_prewarm_state = state;
+            let state = &mut this.state.lock().unwrap();
+            if let LfcPrewarmState::Cancelled = prewarm_state {
+                state.lfc_prewarm_token = CancellationToken::new();
+            }
+            state.lfc_prewarm_state = prewarm_state;
         });
         true
     }
@@ -132,47 +134,70 @@ impl ComputeNode {
 
     /// Request LFC state from endpoint storage and load corresponding pages into Postgres.
     /// Returns a result with `false` if the LFC state is not found in endpoint storage.
-    async fn prewarm_impl(&self, from_endpoint: Option<String>) -> Result<bool> {
+    async fn prewarm_impl(
-        let EndpointStoragePair { url, token } = self.endpoint_storage_pair(from_endpoint)?;
+        &self,
+        from_endpoint: Option<String>,
+        token: CancellationToken,
+    ) -> Result<LfcPrewarmState> {
+        let EndpointStoragePair {
+            url,
+            token: storage_token,
+        } = self.endpoint_storage_pair(from_endpoint)?;
 
         #[cfg(feature = "testing")]
-        fail::fail_point!("compute-prewarm", |_| {
+        fail::fail_point!("compute-prewarm", |_| bail!("compute-prewarm failpoint"));
-            bail!("prewarm configured to fail because of a failpoint")
-        });
 
         info!(%url, "requesting LFC state from endpoint storage");
-        let request = Client::new().get(&url).bearer_auth(token);
+        let request = Client::new().get(&url).bearer_auth(storage_token);
-        let res = request.send().await.context("querying endpoint storage")?;
+        let response = select! {
-        match res.status() {
+            _ = token.cancelled() => return Ok(LfcPrewarmState::Cancelled),
+            response = request.send() => response
+        }
+        .context("querying endpoint storage")?;
+
+        match response.status() {
             StatusCode::OK => (),
-            StatusCode::NOT_FOUND => {
+            StatusCode::NOT_FOUND => return Ok(LfcPrewarmState::Skipped),
-                return Ok(false);
-            }
             status => bail!("{status} querying endpoint storage"),
         }
 
         let mut uncompressed = Vec::new();
-        let lfc_state = res
+        let lfc_state = select! {
-            .bytes()
+            _ = token.cancelled() => return Ok(LfcPrewarmState::Cancelled),
-            .await
+            lfc_state = response.bytes() => lfc_state
-            .context("getting request body from endpoint storage")?;
+        }
-        ZstdDecoder::new(lfc_state.iter().as_slice())
+        .context("getting request body from endpoint storage")?;
-            .read_to_end(&mut uncompressed)
+
-            .await
+        let mut decoder = ZstdDecoder::new(lfc_state.iter().as_slice());
-            .context("decoding LFC state")?;
+        select! {
+            _ = token.cancelled() => return Ok(LfcPrewarmState::Cancelled),
+            read = decoder.read_to_end(&mut uncompressed) => read
+        }
+        .context("decoding LFC state")?;
+
         let uncompressed_len = uncompressed.len();
+        info!(%url, "downloaded LFC state, uncompressed size {uncompressed_len}");
 
-        info!(%url, "downloaded LFC state, uncompressed size {uncompressed_len}, loading into Postgres");
+        // Client connection and prewarm info querying are fast and therefore don't need
-
+        // cancellation
-        ComputeNode::get_maintenance_client(&self.tokio_conn_conf)
+        let client = ComputeNode::get_maintenance_client(&self.tokio_conn_conf)
             .await
-            .context("connecting to postgres")?
+            .context("connecting to postgres")?;
-            .query_one("select neon.prewarm_local_cache($1)", &[&uncompressed])
+        let pg_token = client.cancel_token();
-            .await
-            .context("loading LFC state into postgres")
-            .map(|_| ())?;
 
-        Ok(true)
+        let params: Vec<&(dyn postgres_types::ToSql + Sync)> = vec![&uncompressed];
+        select! {
+            res = client.query_one("select neon.prewarm_local_cache($1)", &params) => res,
+            _ = token.cancelled() => {
+                pg_token.cancel_query(postgres::NoTls).await
+                    .context("cancelling neon.prewarm_local_cache()")?;
+                return Ok(LfcPrewarmState::Cancelled)
+            }
+        }
+        .context("loading LFC state into postgres")
+        .map(|_| ())?;
+
+        Ok(LfcPrewarmState::Completed)
     }
 
     /// If offload request is ongoing, return false, true otherwise
@@ -200,20 +225,20 @@ impl ComputeNode {
 
     async fn offload_lfc_with_state_update(&self) {
         crate::metrics::LFC_OFFLOADS.inc();
-
+        let state = match self.offload_lfc_impl().await {
-        let Err(err) = self.offload_lfc_impl().await else {
+            Ok(state) => state,
-            self.state.lock().unwrap().lfc_offload_state = LfcOffloadState::Completed;
+            Err(err) => {
-            return;
+                crate::metrics::LFC_OFFLOAD_ERRORS.inc();
+                error!(%err, "could not offload LFC");
+                let error = format!("{err:#}");
+                LfcOffloadState::Failed { error }
+            }
         };
 
-        crate::metrics::LFC_OFFLOAD_ERRORS.inc();
+        self.state.lock().unwrap().lfc_offload_state = state;
-        error!(%err, "could not offload LFC state to endpoint storage");
-        self.state.lock().unwrap().lfc_offload_state = LfcOffloadState::Failed {
-            error: format!("{err:#}"),
-        };
     }
 
-    async fn offload_lfc_impl(&self) -> Result<()> {
+    async fn offload_lfc_impl(&self) -> Result<LfcOffloadState> {
         let EndpointStoragePair { url, token } = self.endpoint_storage_pair(None)?;
         info!(%url, "requesting LFC state from Postgres");
 
@@ -228,7 +253,7 @@ impl ComputeNode {
             .context("deserializing LFC state")?;
         let Some(state) = state else {
             info!(%url, "empty LFC state, not exporting");
-            return Ok(());
+            return Ok(LfcOffloadState::Skipped);
         };
 
         let mut compressed = Vec::new();
@@ -242,7 +267,7 @@ impl ComputeNode {
 
         let request = Client::new().put(url).bearer_auth(token).body(compressed);
         match request.send().await {
-            Ok(res) if res.status() == StatusCode::OK => Ok(()),
+            Ok(res) if res.status() == StatusCode::OK => Ok(LfcOffloadState::Completed),
             Ok(res) => bail!(
                 "Request to endpoint storage failed with status: {}",
                 res.status()
@@ -250,4 +275,8 @@ impl ComputeNode {
             Err(err) => Err(err).context("writing to endpoint storage"),
         }
     }
+
+    pub fn cancel_prewarm(self: &Arc<Self>) {
+        self.state.lock().unwrap().lfc_prewarm_token.cancel();
+    }
 }

compute_tools/src/compute_promote.rs

@@ -78,7 +78,7 @@ impl ComputeNode {
         const RETRIES: i32 = 20;
         for i in 0..=RETRIES {
             let row = client
-                .query_one("SELECT pg_last_wal_replay_lsn()", &[])
+                .query_one("SELECT pg_catalog.pg_last_wal_replay_lsn()", &[])
                 .await
                 .context("getting last replay lsn")?;
             let lsn: u64 = row.get::<usize, postgres_types::PgLsn>(0).into();
@@ -103,7 +103,7 @@ impl ComputeNode {
             .await
             .context("setting safekeepers")?;
         client
-            .query("SELECT pg_reload_conf()", &[])
+            .query("SELECT pg_catalog.pg_reload_conf()", &[])
             .await
             .context("reloading postgres config")?;
 
@@ -113,7 +113,7 @@ impl ComputeNode {
         });
 
         let row = client
-            .query_one("SELECT * FROM pg_promote()", &[])
+            .query_one("SELECT * FROM pg_catalog.pg_promote()", &[])
             .await
             .context("pg_promote")?;
         if !row.get::<usize, bool>(0) {

compute_tools/src/config.rs

@@ -8,7 +8,7 @@ use std::path::Path;
 
 use compute_api::responses::TlsConfig;
 use compute_api::spec::{
-    ComputeAudit, ComputeMode, ComputeSpec, DatabricksSettings, GenericOption,
+    ComputeAudit, ComputeMode, ComputeSpec, DatabricksSettings, GenericOption, PageserverProtocol,
 };
 
 use crate::compute::ComputeNodeParams;
@@ -65,15 +65,30 @@ pub fn write_postgres_conf(
         writeln!(file, "{conf}")?;
     }
 
-    // Stripe size GUC should be defined prior to connection string
-    if let Some(stripe_size) = spec.shard_stripe_size {
-        writeln!(file, "neon.stripe_size={stripe_size}")?;
-    }
     // Add options for connecting to storage
     writeln!(file, "# Neon storage settings")?;
     writeln!(file)?;
     if let Some(conninfo) = &spec.pageserver_connection_info {
+        match conninfo.prefer_protocol {
+            PageserverProtocol::Libpq => {
+                writeln!(file, "neon.use_communicator_worker=false")?;
+            }
+            PageserverProtocol::Grpc => {
+                writeln!(file, "neon.use_communicator_worker=true")?;
+            }
+        }
+
+        // Stripe size GUC should be defined prior to connection string
+        if let Some(stripe_size) = conninfo.stripe_size {
+            writeln!(
+                file,
+                "# from compute spec's pageserver_connection_info.stripe_size field"
+            )?;
+            writeln!(file, "neon.stripe_size={stripe_size}")?;
+        }
+
         let mut libpq_urls: Option<Vec<String>> = Some(Vec::new());
+        let mut grpc_urls: Option<Vec<String>> = Some(Vec::new());
         let num_shards = if conninfo.shard_count.0 == 0 {
             1 // unsharded, treat it as a single shard
         } else {
@@ -106,11 +121,19 @@ pub fn write_postgres_conf(
             } else {
                 libpq_urls = None
             }
+            // Similarly for gRPC URLs
+            if let Some(url) = &first_pageserver.grpc_url {
+                if let Some(ref mut urls) = grpc_urls {
+                    urls.push(url.clone());
+                }
+            } else {
+                grpc_urls = None
+            }
         }
         if let Some(libpq_urls) = libpq_urls {
             writeln!(
                 file,
-                "# derived from compute spec's pageserver_conninfo field"
+                "# derived from compute spec's pageserver_connection_info field"
             )?;
             writeln!(
                 file,
@@ -120,24 +143,31 @@ pub fn write_postgres_conf(
         } else {
             writeln!(file, "# no neon.pageserver_connstring")?;
         }
-
+        if let Some(grpc_urls) = grpc_urls {
-        if let Some(stripe_size) = conninfo.stripe_size {
             writeln!(
                 file,
-                "# from compute spec's pageserver_conninfo.stripe_size field"
+                "# derived from compute spec's pageserver_conninfo field"
             )?;
-            writeln!(file, "neon.stripe_size={stripe_size}")?;
+            writeln!(
+                file,
+                "neon.pageserver_grpc_urls={}",
+                escape_conf_value(&grpc_urls.join(","))
+            )?;
+        } else {
+            writeln!(file, "# no neon.pageserver_grpc_urls")?;
         }
     } else {
-        if let Some(s) = &spec.pageserver_connstring {
+        writeln!(file, "neon.use_communicator_worker=false")?;
-            writeln!(file, "# from compute spec's pageserver_connstring field")?;
-            writeln!(file, "neon.pageserver_connstring={}", escape_conf_value(s))?;
-        }
 
+        // Stripe size GUC should be defined prior to connection string
         if let Some(stripe_size) = spec.shard_stripe_size {
             writeln!(file, "# from compute spec's shard_stripe_size field")?;
             writeln!(file, "neon.stripe_size={stripe_size}")?;
         }
+        if let Some(s) = &spec.pageserver_connstring {
+            writeln!(file, "# from compute spec's pageserver_connstring field")?;
+            writeln!(file, "neon.pageserver_connstring={}", escape_conf_value(s))?;
+        }
     }
 
     if !spec.safekeeper_connstrings.is_empty() {

compute_tools/src/http/openapi_spec.yaml

@@ -139,6 +139,15 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/LfcPrewarmState"
+    delete:
+      tags:
+        - Prewarm
+      summary: Cancel ongoing LFC prewarm
+      description: ""
+      operationId: cancelLfcPrewarm
+      responses:
+        202:
+          description: Prewarm cancelled
 
   /lfc/offload:
     post:
@@ -636,7 +645,7 @@ components:
       properties:
         status:
           description: LFC offload status
-          enum: [not_offloaded, offloading, completed, failed]
+          enum: [not_offloaded, offloading, completed, skipped, failed]
           type: string
         error:
           description: LFC offload error, if any

compute_tools/src/http/routes/lfc.rs

@@ -46,3 +46,8 @@ pub(in crate::http) async fn offload(compute: Compute) -> Response {
         )
     }
 }
+
+pub(in crate::http) async fn cancel_prewarm(compute: Compute) -> StatusCode {
+    compute.cancel_prewarm();
+    StatusCode::ACCEPTED
+}

compute_tools/src/http/server.rs

@@ -99,7 +99,12 @@ impl From<&Server> for Router<Arc<ComputeNode>> {
                     );
 
                 let authenticated_router = Router::<Arc<ComputeNode>>::new()
-                    .route("/lfc/prewarm", get(lfc::prewarm_state).post(lfc::prewarm))
+                    .route(
+                        "/lfc/prewarm",
+                        get(lfc::prewarm_state)
+                            .post(lfc::prewarm)
+                            .delete(lfc::cancel_prewarm),
+                    )
                     .route("/lfc/offload", get(lfc::offload_state).post(lfc::offload))
                     .route("/promote", post(promote::promote))
                     .route("/check_writability", post(check_writability::is_writable))

compute_tools/src/installed_extensions.rs

@@ -19,7 +19,7 @@ async fn list_dbs(client: &mut Client) -> Result<Vec<String>, PostgresError> {
         .query(
             "SELECT datname FROM pg_catalog.pg_database
                 WHERE datallowconn
-                AND datconnlimit <> - 2
+                AND datconnlimit OPERATOR(pg_catalog.<>) (OPERATOR(pg_catalog.-) 2::pg_catalog.int4)
                 LIMIT 500",
             &[],
         )
@@ -67,7 +67,7 @@ pub async fn get_installed_extensions(
 
         let extensions: Vec<(String, String, i32)> = client
             .query(
-                "SELECT extname, extversion, extowner::integer FROM pg_catalog.pg_extension",
+                "SELECT extname, extversion, extowner::pg_catalog.int4 FROM pg_catalog.pg_extension",
                 &[],
             )
             .await?

compute_tools/src/lsn_lease.rs

@@ -28,7 +28,10 @@ pub fn launch_lsn_lease_bg_task_for_static(compute: &Arc<ComputeNode>) {
     let compute = compute.clone();
 
     let span = tracing::info_span!("lsn_lease_bg_task", %tenant_id, %timeline_id, %lsn);
+
+    let runtime = tokio::runtime::Handle::current();
     thread::spawn(move || {
+        let _rt_guard = runtime.enter();
         let _entered = span.entered();
         if let Err(e) = lsn_lease_bg_task(compute, tenant_id, timeline_id, lsn) {
             // TODO: might need stronger error feedback than logging an warning.

compute_tools/src/migration.rs

@@ -76,7 +76,7 @@ impl<'m> MigrationRunner<'m> {
         self.client
             .simple_query("CREATE SCHEMA IF NOT EXISTS neon_migration")
             .await?;
-        self.client.simple_query("CREATE TABLE IF NOT EXISTS neon_migration.migration_id (key INT NOT NULL PRIMARY KEY, id bigint NOT NULL DEFAULT 0)").await?;
+        self.client.simple_query("CREATE TABLE IF NOT EXISTS neon_migration.migration_id (key pg_catalog.int4 NOT NULL PRIMARY KEY, id pg_catalog.int8 NOT NULL DEFAULT 0)").await?;
         self.client
             .simple_query(
                 "INSERT INTO neon_migration.migration_id VALUES (0, 0) ON CONFLICT DO NOTHING",

compute_tools/src/migrations/0002-alter_roles.sql

@@ -15,17 +15,17 @@ DO $$
 DECLARE
     role_name text;
 BEGIN
-    FOR role_name IN SELECT rolname FROM pg_roles WHERE pg_has_role(rolname, '{privileged_role_name}', 'member')
+    FOR role_name IN SELECT rolname FROM pg_catalog.pg_roles WHERE pg_catalog.pg_has_role(rolname, '{privileged_role_name}', 'member')
     LOOP
-        RAISE NOTICE 'EXECUTING ALTER ROLE % INHERIT', quote_ident(role_name);
+        RAISE NOTICE 'EXECUTING ALTER ROLE % INHERIT', pg_catalog.quote_ident(role_name);
-        EXECUTE 'ALTER ROLE ' || quote_ident(role_name) || ' INHERIT';
+        EXECUTE pg_catalog.format('ALTER ROLE %I INHERIT;', role_name);
     END LOOP;
 
-    FOR role_name IN SELECT rolname FROM pg_roles
+    FOR role_name IN SELECT rolname FROM pg_catalog.pg_roles
         WHERE
-            NOT pg_has_role(rolname, '{privileged_role_name}', 'member') AND NOT starts_with(rolname, 'pg_')
+            NOT pg_catalog.pg_has_role(rolname, '{privileged_role_name}', 'member') AND NOT pg_catalog.starts_with(rolname, 'pg_')
     LOOP
-        RAISE NOTICE 'EXECUTING ALTER ROLE % NOBYPASSRLS', quote_ident(role_name);
+        RAISE NOTICE 'EXECUTING ALTER ROLE % NOBYPASSRLS', pg_catalog.quote_ident(role_name);
-        EXECUTE 'ALTER ROLE ' || quote_ident(role_name) || ' NOBYPASSRLS';
+        EXECUTE pg_catalog.format('ALTER ROLE %I NOBYPASSRLS;', role_name);
     END LOOP;
 END $$;

compute_tools/src/migrations/0003-grant_pg_create_subscription_to_privileged_role.sql

@@ -1,6 +1,6 @@
 DO $$
 BEGIN
-    IF (SELECT setting::numeric >= 160000 FROM pg_settings WHERE name = 'server_version_num') THEN
+    IF (SELECT setting::pg_catalog.numeric >= 160000 FROM pg_catalog.pg_settings WHERE name = 'server_version_num') THEN
         EXECUTE 'GRANT pg_create_subscription TO {privileged_role_name}';
     END IF;
 END $$;

compute_tools/src/migrations/0009-revoke_replication_for_previously_allowed_roles.sql

@@ -5,9 +5,9 @@ DO $$
 DECLARE
     role_name TEXT;
 BEGIN
-    FOR role_name IN SELECT rolname FROM pg_roles WHERE rolreplication IS TRUE
+    FOR role_name IN SELECT rolname FROM pg_catalog.pg_roles WHERE rolreplication IS TRUE
     LOOP
-        RAISE NOTICE 'EXECUTING ALTER ROLE % NOREPLICATION', quote_ident(role_name);
+        RAISE NOTICE 'EXECUTING ALTER ROLE % NOREPLICATION', pg_catalog.quote_ident(role_name);
-        EXECUTE 'ALTER ROLE ' || quote_ident(role_name) || ' NOREPLICATION';
+        EXECUTE pg_catalog.format('ALTER ROLE %I NOREPLICATION;', role_name);
     END LOOP;
 END $$;

compute_tools/src/migrations/0010-grant_snapshot_synchronization_funcs_to_privileged_role.sql

@@ -1,6 +1,6 @@
 DO $$
 BEGIN
-    IF (SELECT setting::numeric >= 160000 FROM pg_settings WHERE name = 'server_version_num') THEN
+    IF (SELECT setting::pg_catalog.numeric >= 160000 FROM pg_catalog.pg_settings WHERE name OPERATOR(pg_catalog.=) 'server_version_num'::pg_catalog.text) THEN
        EXECUTE 'GRANT EXECUTE ON FUNCTION pg_export_snapshot TO {privileged_role_name}';
        EXECUTE 'GRANT EXECUTE ON FUNCTION pg_log_standby_snapshot TO {privileged_role_name}';
     END IF;

compute_tools/src/migrations/tests/0001-add_bypass_rls_to_privileged_role.sql

@@ -2,7 +2,7 @@ DO $$
 DECLARE
     bypassrls boolean;
 BEGIN
-    SELECT rolbypassrls INTO bypassrls FROM pg_roles WHERE rolname = 'neon_superuser';
+    SELECT rolbypassrls INTO bypassrls FROM pg_catalog.pg_roles WHERE rolname = 'neon_superuser';
     IF NOT bypassrls THEN
         RAISE EXCEPTION 'neon_superuser cannot bypass RLS';
     END IF;

compute_tools/src/migrations/tests/0002-alter_roles.sql

@@ -4,8 +4,8 @@ DECLARE
 BEGIN
     FOR role IN
         SELECT rolname AS name, rolinherit AS inherit
-        FROM pg_roles
+        FROM pg_catalog.pg_roles
-        WHERE pg_has_role(rolname, 'neon_superuser', 'member')
+        WHERE pg_catalog.pg_has_role(rolname, 'neon_superuser', 'member')
     LOOP
         IF NOT role.inherit THEN
             RAISE EXCEPTION '% cannot inherit', quote_ident(role.name);
@@ -14,12 +14,12 @@ BEGIN
 
     FOR role IN
         SELECT rolname AS name, rolbypassrls AS bypassrls
-        FROM pg_roles
+        FROM pg_catalog.pg_roles
-        WHERE NOT pg_has_role(rolname, 'neon_superuser', 'member')
+        WHERE NOT pg_catalog.pg_has_role(rolname, 'neon_superuser', 'member')
-            AND NOT starts_with(rolname, 'pg_')
+            AND NOT pg_catalog.starts_with(rolname, 'pg_')
     LOOP
         IF role.bypassrls THEN
-            RAISE EXCEPTION  '% can bypass RLS', quote_ident(role.name);
+            RAISE EXCEPTION  '% can bypass RLS', pg_catalog.quote_ident(role.name);
         END IF;
     END LOOP;
 END $$;

compute_tools/src/migrations/tests/0003-grant_pg_create_subscription_to_privileged_role.sql

@@ -1,10 +1,10 @@
 DO $$
 BEGIN
-    IF (SELECT current_setting('server_version_num')::numeric < 160000) THEN
+    IF (SELECT pg_catalog.current_setting('server_version_num')::pg_catalog.numeric < 160000) THEN
         RETURN;
     END IF;
 
-    IF NOT (SELECT pg_has_role('neon_superuser', 'pg_create_subscription', 'member')) THEN
+    IF NOT (SELECT pg_catalog.pg_has_role('neon_superuser', 'pg_create_subscription', 'member')) THEN
         RAISE EXCEPTION 'neon_superuser cannot execute pg_create_subscription';
     END IF;
 END $$;

compute_tools/src/migrations/tests/0004-grant_pg_monitor_to_privileged_role.sql

@@ -2,12 +2,12 @@ DO $$
 DECLARE
     monitor record;
 BEGIN
-    SELECT pg_has_role('neon_superuser', 'pg_monitor', 'member') AS member,
+    SELECT pg_catalog.pg_has_role('neon_superuser', 'pg_monitor', 'member') AS member,
             admin_option AS admin
         INTO monitor
-        FROM pg_auth_members
+        FROM pg_catalog.pg_auth_members
-        WHERE roleid = 'pg_monitor'::regrole
+        WHERE roleid = 'pg_monitor'::pg_catalog.regrole
-            AND member = 'neon_superuser'::regrole;
+            AND member = 'neon_superuser'::pg_catalog.regrole;
 
     IF monitor IS NULL THEN
         RAISE EXCEPTION 'no entry in pg_auth_members for neon_superuser and pg_monitor';

compute_tools/src/migrations/tests/0010-grant_snapshot_synchronization_funcs_to_privileged_role.sql

@@ -2,11 +2,11 @@ DO $$
 DECLARE
     can_execute boolean;
 BEGIN
-    SELECT bool_and(has_function_privilege('neon_superuser', oid, 'execute'))
+    SELECT pg_catalog.bool_and(pg_catalog.has_function_privilege('neon_superuser', oid, 'execute'))
        INTO can_execute
-       FROM pg_proc
+       FROM pg_catalog.pg_proc
        WHERE proname IN ('pg_export_snapshot', 'pg_log_standby_snapshot')
-           AND pronamespace = 'pg_catalog'::regnamespace;
+           AND pronamespace = 'pg_catalog'::pg_catalog.regnamespace;
     IF NOT can_execute THEN
         RAISE EXCEPTION 'neon_superuser cannot execute both pg_export_snapshot and pg_log_standby_snapshot';
     END IF;

compute_tools/src/migrations/tests/0011-grant_pg_show_replication_origin_status_to_privileged_role.sql

@@ -2,9 +2,9 @@ DO $$
 DECLARE
     can_execute boolean;
 BEGIN
-    SELECT has_function_privilege('neon_superuser', oid, 'execute')
+    SELECT pg_catalog.has_function_privilege('neon_superuser', oid, 'execute')
        INTO can_execute
-       FROM pg_proc
+       FROM pg_catalog.pg_proc
        WHERE proname = 'pg_show_replication_origin_status'
            AND pronamespace = 'pg_catalog'::regnamespace;
     IF NOT can_execute THEN

compute_tools/src/migrations/tests/0012-grant_pg_signal_backend_to_privileged_role.sql

@@ -2,10 +2,10 @@ DO $$
 DECLARE
     signal_backend record;
 BEGIN
-    SELECT pg_has_role('neon_superuser', 'pg_signal_backend', 'member') AS member,
+    SELECT pg_catalog.pg_has_role('neon_superuser', 'pg_signal_backend', 'member') AS member,
             admin_option AS admin
         INTO signal_backend
-        FROM pg_auth_members
+        FROM pg_catalog.pg_auth_members
         WHERE roleid = 'pg_signal_backend'::regrole
             AND member = 'neon_superuser'::regrole;
 

compute_tools/src/monitor.rs

@@ -407,9 +407,9 @@ fn get_database_stats(cli: &mut Client) -> anyhow::Result<(f64, i64)> {
     // like `postgres_exporter` use it to query Postgres statistics.
     // Use explicit 8 bytes type casts to match Rust types.
     let stats = cli.query_one(
-        "SELECT coalesce(sum(active_time), 0.0)::float8 AS total_active_time,
+        "SELECT pg_catalog.coalesce(pg_catalog.sum(active_time), 0.0)::pg_catalog.float8 AS total_active_time,
-            coalesce(sum(sessions), 0)::bigint AS total_sessions
+            pg_catalog.coalesce(pg_catalog.sum(sessions), 0)::pg_catalog.bigint AS total_sessions
-        FROM pg_stat_database
+        FROM pg_catalog.pg_stat_database
         WHERE datname NOT IN (
                 'postgres',
                 'template0',
@@ -445,11 +445,11 @@ fn get_backends_state_change(cli: &mut Client) -> anyhow::Result<Option<DateTime
     let mut last_active: Option<DateTime<Utc>> = None;
     // Get all running client backends except ourself, use RFC3339 DateTime format.
     let backends = cli.query(
-        "SELECT state, to_char(state_change, 'YYYY-MM-DD\"T\"HH24:MI:SS.US\"Z\"') AS state_change
+        "SELECT state, pg_catalog.to_char(state_change, 'YYYY-MM-DD\"T\"HH24:MI:SS.US\"Z\"'::pg_catalog.text) AS state_change
                 FROM pg_stat_activity
-                    WHERE backend_type = 'client backend'
+                    WHERE backend_type OPERATOR(pg_catalog.=) 'client backend'::pg_catalog.text
-                    AND pid != pg_backend_pid()
+                    AND pid OPERATOR(pg_catalog.!=) pg_catalog.pg_backend_pid()
-                    AND usename != 'cloud_admin';", // XXX: find a better way to filter other monitors?
+                    AND usename OPERATOR(pg_catalog.!=) 'cloud_admin'::pg_catalog.name;", // XXX: find a better way to filter other monitors?
         &[],
     );
 

compute_tools/src/pg_helpers.rs

@@ -299,9 +299,9 @@ pub async fn get_existing_dbs_async(
         .query_raw::<str, &String, &[String; 0]>(
             "SELECT
                 datname AS name,
-                (SELECT rolname FROM pg_roles WHERE oid = datdba) AS owner,
+                (SELECT rolname FROM pg_catalog.pg_roles WHERE oid OPERATOR(pg_catalog.=) datdba) AS owner,
                 NOT datallowconn AS restrict_conn,
-                datconnlimit = - 2 AS invalid
+                datconnlimit OPERATOR(pg_catalog.=) (OPERATOR(pg_catalog.-) 2) AS invalid
             FROM
                 pg_catalog.pg_database;",
             &[],

compute_tools/src/spec_apply.rs

@@ -82,7 +82,7 @@ impl ComputeNode {
                 info!("Checking if drop subscription operation was already performed for timeline_id: {}", timeline_id);
 
                 drop_subscriptions_done = match
-                    client.query("select 1 from neon.drop_subscriptions_done where timeline_id = $1", &[&timeline_id.to_string()]).await {
+                    client.query("select 1 from neon.drop_subscriptions_done where timeline_id OPERATOR(pg_catalog.=) $1", &[&timeline_id.to_string()]).await {
                     Ok(result) => !result.is_empty(),
                     Err(e) =>
                     {
@@ -1142,7 +1142,9 @@ async fn get_operations<'a>(
             if let Some(libs) = spec.cluster.settings.find("shared_preload_libraries") {
                 if libs.contains("pg_stat_statements") {
                     return Ok(Box::new(once(Operation {
-                        query: String::from("CREATE EXTENSION IF NOT EXISTS pg_stat_statements"),
+                        query: String::from(
+                            "CREATE EXTENSION IF NOT EXISTS pg_stat_statements WITH SCHEMA public",
+                        ),
                         comment: Some(String::from("create system extensions")),
                     })));
                 }
@@ -1150,11 +1152,13 @@ async fn get_operations<'a>(
             Ok(Box::new(empty()))
         }
         ApplySpecPhase::CreatePgauditExtension => Ok(Box::new(once(Operation {
-            query: String::from("CREATE EXTENSION IF NOT EXISTS pgaudit"),
+            query: String::from("CREATE EXTENSION IF NOT EXISTS pgaudit WITH SCHEMA public"),
             comment: Some(String::from("create pgaudit extensions")),
         }))),
         ApplySpecPhase::CreatePgauditlogtofileExtension => Ok(Box::new(once(Operation {
-            query: String::from("CREATE EXTENSION IF NOT EXISTS pgauditlogtofile"),
+            query: String::from(
+                "CREATE EXTENSION IF NOT EXISTS pgauditlogtofile WITH SCHEMA public",
+            ),
             comment: Some(String::from("create pgauditlogtofile extensions")),
         }))),
         // Disable pgaudit logging for postgres database.
@@ -1178,7 +1182,7 @@ async fn get_operations<'a>(
                 },
                 Operation {
                     query: String::from(
-                        "UPDATE pg_extension SET extrelocatable = true WHERE extname = 'neon'",
+                        "UPDATE pg_catalog.pg_extension SET extrelocatable = true WHERE extname OPERATOR(pg_catalog.=) 'neon'::pg_catalog.name AND extrelocatable OPERATOR(pg_catalog.=) false",
                     ),
                     comment: Some(String::from("compat/fix: make neon relocatable")),
                 },

compute_tools/src/sql/add_availabilitycheck_tables.sql

@@ -3,16 +3,17 @@ BEGIN
     IF NOT EXISTS(
         SELECT 1
         FROM pg_catalog.pg_tables
-        WHERE tablename = 'health_check'
+        WHERE tablename::pg_catalog.name OPERATOR(pg_catalog.=) 'health_check'::pg_catalog.name
+        AND schemaname::pg_catalog.name OPERATOR(pg_catalog.=) 'public'::pg_catalog.name
     )
     THEN
-    CREATE TABLE health_check (
+    CREATE TABLE public.health_check (
-        id serial primary key,
+        id pg_catalog.int4 primary key generated by default as identity,
-        updated_at timestamptz default now()
+        updated_at pg_catalog.timestamptz default pg_catalog.now()
     );
-    INSERT INTO health_check VALUES (1, now())
+    INSERT INTO public.health_check VALUES (1, pg_catalog.now())
         ON CONFLICT (id) DO UPDATE
-         SET updated_at = now();
+         SET updated_at = pg_catalog.now();
     END IF;
 END
 $$

compute_tools/src/sql/anon_ext_fn_reassign.sql

@@ -1,12 +0,0 @@
-DO $$
-DECLARE
-    query varchar;
-BEGIN
-    FOR query IN SELECT 'ALTER FUNCTION '||nsp.nspname||'.'||p.proname||'('||pg_get_function_identity_arguments(p.oid)||') OWNER TO {db_owner};'
-    FROM pg_proc p
-        JOIN pg_namespace nsp ON p.pronamespace = nsp.oid
-    WHERE nsp.nspname = 'anon' LOOP
-        EXECUTE query;
-    END LOOP;
-END
-$$;

compute_tools/src/sql/create_privileged_role.sql

@@ -1,6 +1,6 @@
 DO $$
     BEGIN
-        IF NOT EXISTS (SELECT FROM pg_catalog.pg_roles WHERE rolname = '{privileged_role_name}')
+        IF NOT EXISTS (SELECT FROM pg_catalog.pg_roles WHERE rolname OPERATOR(pg_catalog.=) '{privileged_role_name}'::pg_catalog.name)
         THEN
             CREATE ROLE {privileged_role_name} {privileges} IN ROLE pg_read_all_data, pg_write_all_data;
         END IF;

compute_tools/src/sql/default_grants.sql

@@ -4,14 +4,14 @@ $$
         IF EXISTS(
             SELECT nspname
             FROM pg_catalog.pg_namespace
-            WHERE nspname = 'public'
+            WHERE nspname OPERATOR(pg_catalog.=) 'public'
         ) AND
-           current_setting('server_version_num')::int / 10000 >= 15
+           pg_catalog.current_setting('server_version_num')::int OPERATOR(pg_catalog./) 10000 OPERATOR(pg_catalog.>=) 15
         THEN
             IF EXISTS(
                 SELECT rolname
                 FROM pg_catalog.pg_roles
-                WHERE rolname = 'web_access'
+                WHERE rolname OPERATOR(pg_catalog.=) 'web_access'
             )
             THEN
                 GRANT CREATE ON SCHEMA public TO web_access;
@@ -20,7 +20,7 @@ $$
         IF EXISTS(
             SELECT nspname
             FROM pg_catalog.pg_namespace
-            WHERE nspname = 'public'
+            WHERE nspname OPERATOR(pg_catalog.=) 'public'
         )
         THEN
             ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT ALL ON TABLES TO neon_superuser WITH GRANT OPTION;

compute_tools/src/sql/drop_subscriptions.sql

@@ -2,11 +2,17 @@ DO ${outer_tag}$
 DECLARE
     subname TEXT;
 BEGIN
-    LOCK TABLE pg_subscription IN ACCESS EXCLUSIVE MODE;
+    LOCK TABLE pg_catalog.pg_subscription IN ACCESS EXCLUSIVE MODE;
-    FOR subname IN SELECT pg_subscription.subname FROM pg_subscription WHERE subdbid = (SELECT oid FROM pg_database WHERE datname = {datname_str}) LOOP
+    FOR subname IN
-        EXECUTE format('ALTER SUBSCRIPTION %I DISABLE;', subname);
+        SELECT pg_subscription.subname
-        EXECUTE format('ALTER SUBSCRIPTION %I SET (slot_name = NONE);', subname);
+        FROM pg_catalog.pg_subscription
-        EXECUTE format('DROP SUBSCRIPTION %I;', subname);
+        WHERE subdbid OPERATOR(pg_catalog.=) (
+            SELECT oid FROM pg_database WHERE datname OPERATOR(pg_catalog.=) {datname_str}::pg_catalog.name
+        )
+    LOOP
+        EXECUTE pg_catalog.format('ALTER SUBSCRIPTION %I DISABLE;', subname);
+        EXECUTE pg_catalog.format('ALTER SUBSCRIPTION %I SET (slot_name = NONE);', subname);
+        EXECUTE pg_catalog.format('DROP SUBSCRIPTION %I;', subname);
     END LOOP;
 END;
 ${outer_tag}$;

compute_tools/src/sql/finalize_drop_subscriptions.sql

@@ -3,19 +3,19 @@ BEGIN
     IF NOT EXISTS(
         SELECT 1
         FROM pg_catalog.pg_tables
-        WHERE tablename = 'drop_subscriptions_done'
+        WHERE tablename OPERATOR(pg_catalog.=) 'drop_subscriptions_done'::pg_catalog.name
-        AND schemaname = 'neon'
+        AND schemaname OPERATOR(pg_catalog.=) 'neon'::pg_catalog.name
     )
     THEN
         CREATE TABLE neon.drop_subscriptions_done
-        (id serial primary key, timeline_id text);
+        (id pg_catalog.int4 primary key generated by default as identity, timeline_id pg_catalog.text);
     END IF;
 
     -- preserve the timeline_id of the last drop_subscriptions run
     -- to ensure that the cleanup of a timeline is executed only once.
     -- use upsert to avoid the table bloat in case of cascade branching (branch of a branch)
-    INSERT INTO neon.drop_subscriptions_done VALUES (1, current_setting('neon.timeline_id'))
+    INSERT INTO neon.drop_subscriptions_done VALUES (1, pg_catalog.current_setting('neon.timeline_id'))
     ON CONFLICT (id) DO UPDATE
-    SET timeline_id = current_setting('neon.timeline_id');
+    SET timeline_id = pg_catalog.current_setting('neon.timeline_id')::pg_catalog.text;
 END
 $$

compute_tools/src/sql/pre_drop_role_revoke_privileges.sql

@@ -15,15 +15,15 @@ BEGIN
         WHERE schema_name IN ('public')
     LOOP
         FOR grantor IN EXECUTE
-            format(
+            pg_catalog.format(
-                'SELECT DISTINCT rtg.grantor FROM information_schema.role_table_grants AS rtg WHERE grantee = %s',
+                'SELECT DISTINCT rtg.grantor FROM information_schema.role_table_grants AS rtg WHERE grantee OPERATOR(pg_catalog.=) %s',
                 -- N.B. this has to be properly dollar-escaped with `pg_quote_dollar()`
                 quote_literal({role_name})
             )
         LOOP
-            EXECUTE format('SET LOCAL ROLE %I', grantor);
+            EXECUTE pg_catalog.format('SET LOCAL ROLE %I', grantor);
 
-            revoke_query := format(
+            revoke_query := pg_catalog.format(
                 'REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA %I FROM %I GRANTED BY %I',
                 schema,
                 -- N.B. this has to be properly dollar-escaped with `pg_quote_dollar()`

compute_tools/src/sql/set_public_schema_owner.sql

@@ -5,17 +5,17 @@ DO ${outer_tag}$
         IF EXISTS(
             SELECT nspname
             FROM pg_catalog.pg_namespace
-            WHERE nspname = 'public'
+            WHERE nspname OPERATOR(pg_catalog.=) 'public'::pg_catalog.name
         )
         THEN
             SELECT nspowner::regrole::text
             FROM pg_catalog.pg_namespace
-            WHERE nspname = 'public'
+            WHERE nspname OPERATOR(pg_catalog.=) 'public'::pg_catalog.text
             INTO schema_owner;
 
-            IF schema_owner = 'cloud_admin' OR schema_owner = 'zenith_admin'
+            IF schema_owner OPERATOR(pg_catalog.=) 'cloud_admin'::pg_catalog.text OR schema_owner OPERATOR(pg_catalog.=) 'zenith_admin'::pg_catalog.text
             THEN
-                EXECUTE format('ALTER SCHEMA public OWNER TO %I', {db_owner});
+                EXECUTE pg_catalog.format('ALTER SCHEMA public OWNER TO %I', {db_owner});
             END IF;
         END IF;
     END

compute_tools/src/sql/unset_template_for_drop_dbs.sql

@@ -3,10 +3,10 @@ DO ${outer_tag}$
         IF EXISTS(
             SELECT 1
             FROM pg_catalog.pg_database
-            WHERE datname = {datname}
+            WHERE datname OPERATOR(pg_catalog.=) {datname}::pg_catalog.name
         )
         THEN
-            EXECUTE format('ALTER DATABASE %I is_template false', {datname});
+            EXECUTE pg_catalog.format('ALTER DATABASE %I is_template false', {datname});
         END IF;
     END
 ${outer_tag}$;

control_plane/src/bin/neon_local.rs

@@ -71,8 +71,9 @@ const DEFAULT_PG_VERSION_NUM: &str = "17";
 
 const DEFAULT_PAGESERVER_CONTROL_PLANE_API: &str = "http://127.0.0.1:1234/upcall/v1/";
 
+/// Neon CLI.
 #[derive(clap::Parser)]
-#[command(version = GIT_VERSION, about, name = "Neon CLI")]
+#[command(version = GIT_VERSION, name = "Neon CLI")]
 struct Cli {
     #[command(subcommand)]
     command: NeonLocalCmd,
@@ -107,30 +108,31 @@ enum NeonLocalCmd {
     Stop(StopCmdArgs),
 }
 
+/// Initialize a new Neon repository, preparing configs for services to start with.
 #[derive(clap::Args)]
-#[clap(about = "Initialize a new Neon repository, preparing configs for services to start with")]
 struct InitCmdArgs {
-    #[clap(long, help("How many pageservers to create (default 1)"))]
+    /// How many pageservers to create (default 1).
+    #[clap(long)]
     num_pageservers: Option<u16>,
 
     #[clap(long)]
     config: Option<PathBuf>,
 
-    #[clap(long, help("Force initialization even if the repository is not empty"))]
+    /// Force initialization even if the repository is not empty.
+    #[clap(long, default_value = "must-not-exist")]
     #[arg(value_parser)]
-    #[clap(default_value = "must-not-exist")]
     force: InitForceMode,
 }
 
+/// Start pageserver and safekeepers.
 #[derive(clap::Args)]
-#[clap(about = "Start pageserver and safekeepers")]
 struct StartCmdArgs {
     #[clap(long = "start-timeout", default_value = "10s")]
     timeout: humantime::Duration,
 }
 
+/// Stop pageserver and safekeepers.
 #[derive(clap::Args)]
-#[clap(about = "Stop pageserver and safekeepers")]
 struct StopCmdArgs {
     #[arg(value_enum)]
     #[clap(long, default_value_t = StopMode::Fast)]
@@ -143,8 +145,8 @@ enum StopMode {
     Immediate,
 }
 
+/// Manage tenants.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage tenants")]
 enum TenantCmd {
     List,
     Create(TenantCreateCmdArgs),
@@ -155,38 +157,36 @@ enum TenantCmd {
 
 #[derive(clap::Args)]
 struct TenantCreateCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
 
-    #[clap(
+    /// Use a specific timeline id when creating a tenant and its initial timeline.
-        long,
+    #[clap(long)]
-        help = "Use a specific timeline id when creating a tenant and its initial timeline"
-    )]
     timeline_id: Option<TimelineId>,
 
     #[clap(short = 'c')]
     config: Vec<String>,
 
+    /// Postgres version to use for the initial timeline.
     #[arg(default_value = DEFAULT_PG_VERSION_NUM)]
-    #[clap(long, help = "Postgres version to use for the initial timeline")]
+    #[clap(long)]
     pg_version: PgMajorVersion,
 
-    #[clap(
+    /// Use this tenant in future CLI commands where tenant_id is needed, but not specified.
-        long,
+    #[clap(long)]
-        help = "Use this tenant in future CLI commands where tenant_id is needed, but not specified"
-    )]
     set_default: bool,
 
-    #[clap(long, help = "Number of shards in the new tenant")]
+    /// Number of shards in the new tenant.
+    #[clap(long)]
     #[arg(default_value_t = 0)]
     shard_count: u8,
-    #[clap(long, help = "Sharding stripe size in pages")]
+    /// Sharding stripe size in pages.
+    #[clap(long)]
     shard_stripe_size: Option<u32>,
 
-    #[clap(long, help = "Placement policy shards in this tenant")]
+    /// Placement policy shards in this tenant.
+    #[clap(long)]
     #[arg(value_parser = parse_placement_policy)]
     placement_policy: Option<PlacementPolicy>,
 }
@@ -195,44 +195,35 @@ fn parse_placement_policy(s: &str) -> anyhow::Result<PlacementPolicy> {
     Ok(serde_json::from_str::<PlacementPolicy>(s)?)
 }
 
+/// Set a particular tenant as default in future CLI commands where tenant_id is needed, but not
+/// specified.
 #[derive(clap::Args)]
-#[clap(
-    about = "Set a particular tenant as default in future CLI commands where tenant_id is needed, but not specified"
-)]
 struct TenantSetDefaultCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: TenantId,
 }
 
 #[derive(clap::Args)]
 struct TenantConfigCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
 
     #[clap(short = 'c')]
     config: Vec<String>,
 }
 
+/// Import a tenant that is present in remote storage, and create branches for its timelines.
 #[derive(clap::Args)]
-#[clap(
-    about = "Import a tenant that is present in remote storage, and create branches for its timelines"
-)]
 struct TenantImportCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: TenantId,
 }
 
+/// Manage timelines.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage timelines")]
 enum TimelineCmd {
     List(TimelineListCmdArgs),
     Branch(TimelineBranchCmdArgs),
@@ -240,98 +231,87 @@ enum TimelineCmd {
     Import(TimelineImportCmdArgs),
 }
 
+/// List all timelines available to this pageserver.
 #[derive(clap::Args)]
-#[clap(about = "List all timelines available to this pageserver")]
 struct TimelineListCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_shard_id: Option<TenantShardId>,
 }
 
+/// Create a new timeline, branching off from another timeline.
 #[derive(clap::Args)]
-#[clap(about = "Create a new timeline, branching off from another timeline")]
 struct TimelineBranchCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
-
+    /// New timeline's ID, as a 32-byte hexadecimal string.
-    #[clap(long, help = "New timeline's ID")]
+    #[clap(long)]
     timeline_id: Option<TimelineId>,
-
+    /// Human-readable alias for the new timeline.
-    #[clap(long, help = "Human-readable alias for the new timeline")]
+    #[clap(long)]
     branch_name: String,
-
+    /// Use last Lsn of another timeline (and its data) as base when creating the new timeline. The
-    #[clap(
+    /// timeline gets resolved by its branch name.
-        long,
+    #[clap(long)]
-        help = "Use last Lsn of another timeline (and its data) as base when creating the new timeline. The timeline gets resolved by its branch name."
-    )]
     ancestor_branch_name: Option<String>,
-
+    /// When using another timeline as base, use a specific Lsn in it instead of the latest one.
-    #[clap(
+    #[clap(long)]
-        long,
-        help = "When using another timeline as base, use a specific Lsn in it instead of the latest one"
-    )]
     ancestor_start_lsn: Option<Lsn>,
 }
 
+/// Create a new blank timeline.
 #[derive(clap::Args)]
-#[clap(about = "Create a new blank timeline")]
 struct TimelineCreateCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
-
+    /// New timeline's ID, as a 32-byte hexadecimal string.
-    #[clap(long, help = "New timeline's ID")]
+    #[clap(long)]
     timeline_id: Option<TimelineId>,
-
+    /// Human-readable alias for the new timeline.
-    #[clap(long, help = "Human-readable alias for the new timeline")]
+    #[clap(long)]
     branch_name: String,
 
+    /// Postgres version.
     #[arg(default_value = DEFAULT_PG_VERSION_NUM)]
-    #[clap(long, help = "Postgres version")]
+    #[clap(long)]
     pg_version: PgMajorVersion,
 }
 
+/// Import a timeline from a basebackup directory.
 #[derive(clap::Args)]
-#[clap(about = "Import timeline from a basebackup directory")]
 struct TimelineImportCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
-
+    /// New timeline's ID, as a 32-byte hexadecimal string.
-    #[clap(long, help = "New timeline's ID")]
+    #[clap(long)]
     timeline_id: TimelineId,
-
+    /// Human-readable alias for the new timeline.
-    #[clap(long, help = "Human-readable alias for the new timeline")]
+    #[clap(long)]
     branch_name: String,
-
+    /// Basebackup tarfile to import.
-    #[clap(long, help = "Basebackup tarfile to import")]
+    #[clap(long)]
     base_tarfile: PathBuf,
-
+    /// LSN the basebackup starts at.
-    #[clap(long, help = "Lsn the basebackup starts at")]
+    #[clap(long)]
     base_lsn: Lsn,
-
+    /// WAL to add after base.
-    #[clap(long, help = "Wal to add after base")]
+    #[clap(long)]
     wal_tarfile: Option<PathBuf>,
-
+    /// LSN the basebackup ends at.
-    #[clap(long, help = "Lsn the basebackup ends at")]
+    #[clap(long)]
     end_lsn: Option<Lsn>,
 
+    /// Postgres version of the basebackup being imported.
     #[arg(default_value = DEFAULT_PG_VERSION_NUM)]
-    #[clap(long, help = "Postgres version of the backup being imported")]
+    #[clap(long)]
     pg_version: PgMajorVersion,
 }
 
+/// Manage pageservers.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage pageservers")]
 enum PageserverCmd {
     Status(PageserverStatusCmdArgs),
     Start(PageserverStartCmdArgs),
@@ -339,223 +319,202 @@ enum PageserverCmd {
     Restart(PageserverRestartCmdArgs),
 }
 
+/// Show status of a local pageserver.
 #[derive(clap::Args)]
-#[clap(about = "Show status of a local pageserver")]
 struct PageserverStatusCmdArgs {
-    #[clap(long = "id", help = "pageserver id")]
+    /// Pageserver ID.
+    #[clap(long = "id")]
     pageserver_id: Option<NodeId>,
 }
 
+/// Start local pageserver.
 #[derive(clap::Args)]
-#[clap(about = "Start local pageserver")]
 struct PageserverStartCmdArgs {
-    #[clap(long = "id", help = "pageserver id")]
+    /// Pageserver ID.
+    #[clap(long = "id")]
     pageserver_id: Option<NodeId>,
-
+    /// Timeout until we fail the command.
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    #[clap(short = 't', long)]
     #[arg(default_value = "10s")]
     start_timeout: humantime::Duration,
 }
 
+/// Stop local pageserver.
 #[derive(clap::Args)]
-#[clap(about = "Stop local pageserver")]
 struct PageserverStopCmdArgs {
-    #[clap(long = "id", help = "pageserver id")]
+    /// Pageserver ID.
+    #[clap(long = "id")]
     pageserver_id: Option<NodeId>,
-
+    /// If 'immediate', don't flush repository data at shutdown
-    #[clap(
+    #[clap(short = 'm')]
-        short = 'm',
-        help = "If 'immediate', don't flush repository data at shutdown"
-    )]
     #[arg(value_enum, default_value = "fast")]
     stop_mode: StopMode,
 }
 
+/// Restart local pageserver.
 #[derive(clap::Args)]
-#[clap(about = "Restart local pageserver")]
 struct PageserverRestartCmdArgs {
-    #[clap(long = "id", help = "pageserver id")]
+    /// Pageserver ID.
+    #[clap(long = "id")]
     pageserver_id: Option<NodeId>,
-
+    /// Timeout until we fail the command.
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    #[clap(short = 't', long)]
     #[arg(default_value = "10s")]
     start_timeout: humantime::Duration,
 }
 
+/// Manage storage controller.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage storage controller")]
 enum StorageControllerCmd {
     Start(StorageControllerStartCmdArgs),
     Stop(StorageControllerStopCmdArgs),
 }
 
+/// Start storage controller.
 #[derive(clap::Args)]
-#[clap(about = "Start storage controller")]
 struct StorageControllerStartCmdArgs {
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    /// Timeout until we fail the command.
+    #[clap(short = 't', long)]
     #[arg(default_value = "10s")]
     start_timeout: humantime::Duration,
-
+    /// Identifier used to distinguish storage controller instances.
-    #[clap(
+    #[clap(long)]
-        long,
-        help = "Identifier used to distinguish storage controller instances"
-    )]
     #[arg(default_value_t = 1)]
     instance_id: u8,
-
+    /// Base port for the storage controller instance identified by instance-id (defaults to
-    #[clap(
+    /// pageserver cplane api).
-        long,
+    #[clap(long)]
-        help = "Base port for the storage controller instance idenfified by instance-id (defaults to pageserver cplane api)"
-    )]
     base_port: Option<u16>,
 
-    #[clap(
+    /// Whether the storage controller should handle pageserver-reported local disk loss events.
-        long,
+    #[clap(long)]
-        help = "Whether the storage controller should handle pageserver-reported local disk loss events."
-    )]
     handle_ps_local_disk_loss: Option<bool>,
 }
 
+/// Stop storage controller.
 #[derive(clap::Args)]
-#[clap(about = "Stop storage controller")]
 struct StorageControllerStopCmdArgs {
-    #[clap(
+    /// If 'immediate', don't flush repository data at shutdown
-        short = 'm',
+    #[clap(short = 'm')]
-        help = "If 'immediate', don't flush repository data at shutdown"
-    )]
     #[arg(value_enum, default_value = "fast")]
     stop_mode: StopMode,
-
+    /// Identifier used to distinguish storage controller instances.
-    #[clap(
+    #[clap(long)]
-        long,
-        help = "Identifier used to distinguish storage controller instances"
-    )]
     #[arg(default_value_t = 1)]
     instance_id: u8,
 }
 
+/// Manage storage broker.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage storage broker")]
 enum StorageBrokerCmd {
     Start(StorageBrokerStartCmdArgs),
     Stop(StorageBrokerStopCmdArgs),
 }
 
+/// Start broker.
 #[derive(clap::Args)]
-#[clap(about = "Start broker")]
 struct StorageBrokerStartCmdArgs {
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    /// Timeout until we fail the command.
-    #[arg(default_value = "10s")]
+    #[clap(short = 't', long, default_value = "10s")]
     start_timeout: humantime::Duration,
 }
 
+/// Stop broker.
 #[derive(clap::Args)]
-#[clap(about = "stop broker")]
 struct StorageBrokerStopCmdArgs {
-    #[clap(
+    /// If 'immediate', don't flush repository data on shutdown.
-        short = 'm',
+    #[clap(short = 'm')]
-        help = "If 'immediate', don't flush repository data at shutdown"
-    )]
     #[arg(value_enum, default_value = "fast")]
     stop_mode: StopMode,
 }
 
+/// Manage safekeepers.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage safekeepers")]
 enum SafekeeperCmd {
     Start(SafekeeperStartCmdArgs),
     Stop(SafekeeperStopCmdArgs),
     Restart(SafekeeperRestartCmdArgs),
 }
 
+/// Manage object storage.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage object storage")]
 enum EndpointStorageCmd {
     Start(EndpointStorageStartCmd),
     Stop(EndpointStorageStopCmd),
 }
 
+/// Start object storage.
 #[derive(clap::Args)]
-#[clap(about = "Start object storage")]
 struct EndpointStorageStartCmd {
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    /// Timeout until we fail the command.
+    #[clap(short = 't', long)]
     #[arg(default_value = "10s")]
     start_timeout: humantime::Duration,
 }
 
+/// Stop object storage.
 #[derive(clap::Args)]
-#[clap(about = "Stop object storage")]
 struct EndpointStorageStopCmd {
+    /// If 'immediate', don't flush repository data on shutdown.
+    #[clap(short = 'm')]
     #[arg(value_enum, default_value = "fast")]
-    #[clap(
-        short = 'm',
-        help = "If 'immediate', don't flush repository data at shutdown"
-    )]
     stop_mode: StopMode,
 }
 
+/// Start local safekeeper.
 #[derive(clap::Args)]
-#[clap(about = "Start local safekeeper")]
 struct SafekeeperStartCmdArgs {
-    #[clap(help = "safekeeper id")]
+    /// Safekeeper ID.
     #[arg(default_value_t = NodeId(1))]
     id: NodeId,
 
-    #[clap(
+    /// Additional safekeeper invocation options, e.g. -e=--http-auth-public-key-path=foo.
-        short = 'e',
+    #[clap(short = 'e', long = "safekeeper-extra-opt")]
-        long = "safekeeper-extra-opt",
-        help = "Additional safekeeper invocation options, e.g. -e=--http-auth-public-key-path=foo"
-    )]
     extra_opt: Vec<String>,
 
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    /// Timeout until we fail the command.
+    #[clap(short = 't', long)]
     #[arg(default_value = "10s")]
     start_timeout: humantime::Duration,
 }
 
+/// Stop local safekeeper.
 #[derive(clap::Args)]
-#[clap(about = "Stop local safekeeper")]
 struct SafekeeperStopCmdArgs {
-    #[clap(help = "safekeeper id")]
+    /// Safekeeper ID.
     #[arg(default_value_t = NodeId(1))]
     id: NodeId,
 
+    /// If 'immediate', don't flush repository data on shutdown.
     #[arg(value_enum, default_value = "fast")]
-    #[clap(
+    #[clap(short = 'm')]
-        short = 'm',
-        help = "If 'immediate', don't flush repository data at shutdown"
-    )]
     stop_mode: StopMode,
 }
 
+/// Restart local safekeeper.
 #[derive(clap::Args)]
-#[clap(about = "Restart local safekeeper")]
 struct SafekeeperRestartCmdArgs {
-    #[clap(help = "safekeeper id")]
+    /// Safekeeper ID.
     #[arg(default_value_t = NodeId(1))]
     id: NodeId,
 
+    /// If 'immediate', don't flush repository data on shutdown.
     #[arg(value_enum, default_value = "fast")]
-    #[clap(
+    #[clap(short = 'm')]
-        short = 'm',
-        help = "If 'immediate', don't flush repository data at shutdown"
-    )]
     stop_mode: StopMode,
 
-    #[clap(
+    /// Additional safekeeper invocation options, e.g. -e=--http-auth-public-key-path=foo.
-        short = 'e',
+    #[clap(short = 'e', long = "safekeeper-extra-opt")]
-        long = "safekeeper-extra-opt",
-        help = "Additional safekeeper invocation options, e.g. -e=--http-auth-public-key-path=foo"
-    )]
     extra_opt: Vec<String>,
 
-    #[clap(short = 't', long, help = "timeout until we fail the command")]
+    /// Timeout until we fail the command.
+    #[clap(short = 't', long)]
     #[arg(default_value = "10s")]
     start_timeout: humantime::Duration,
 }
 
+/// Manage Postgres instances.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage Postgres instances")]
 enum EndpointCmd {
     List(EndpointListCmdArgs),
     Create(EndpointCreateCmdArgs),
@@ -567,33 +526,27 @@ enum EndpointCmd {
     GenerateJwt(EndpointGenerateJwtCmdArgs),
 }
 
+/// List endpoints.
 #[derive(clap::Args)]
-#[clap(about = "List endpoints")]
 struct EndpointListCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_shard_id: Option<TenantShardId>,
 }
 
+/// Create a compute endpoint.
 #[derive(clap::Args)]
-#[clap(about = "Create a compute endpoint")]
 struct EndpointCreateCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
-
+    /// Postgres endpoint ID.
-    #[clap(help = "Postgres endpoint id")]
     endpoint_id: Option<String>,
-    #[clap(long, help = "Name of the branch the endpoint will run on")]
+    /// Name of the branch the endpoint will run on.
+    #[clap(long)]
     branch_name: Option<String>,
-    #[clap(
+    /// Specify LSN on the timeline to start from. By default, end of the timeline would be used.
-        long,
+    #[clap(long)]
-        help = "Specify Lsn on the timeline to start from. By default, end of the timeline would be used"
-    )]
     lsn: Option<Lsn>,
     #[clap(long)]
     pg_port: Option<u16>,
@@ -604,16 +557,13 @@ struct EndpointCreateCmdArgs {
     #[clap(long = "pageserver-id")]
     endpoint_pageserver_id: Option<NodeId>,
 
-    #[clap(
+    /// Don't do basebackup, create endpoint directory with only config files.
-        long,
+    #[clap(long, action = clap::ArgAction::Set, default_value_t = false)]
-        help = "Don't do basebackup, create endpoint directory with only config files",
-        action = clap::ArgAction::Set,
-        default_value_t = false
-    )]
     config_only: bool,
 
+    /// Postgres version.
     #[arg(default_value = DEFAULT_PG_VERSION_NUM)]
-    #[clap(long, help = "Postgres version")]
+    #[clap(long)]
     pg_version: PgMajorVersion,
 
     /// Use gRPC to communicate with Pageservers, by generating grpc:// connstrings.
@@ -624,170 +574,140 @@ struct EndpointCreateCmdArgs {
     #[clap(long)]
     grpc: bool,
 
-    #[clap(
+    /// If set, the node will be a hot replica on the specified timeline.
-        long,
+    #[clap(long, action = clap::ArgAction::Set, default_value_t = false)]
-        help = "If set, the node will be a hot replica on the specified timeline",
-        action = clap::ArgAction::Set,
-        default_value_t = false
-    )]
     hot_standby: bool,
-
+    /// If set, will set up the catalog for neon_superuser.
-    #[clap(long, help = "If set, will set up the catalog for neon_superuser")]
+    #[clap(long)]
     update_catalog: bool,
-
+    /// Allow multiple primary endpoints running on the same branch. Shouldn't be used normally, but
-    #[clap(
+    /// useful for tests.
-        long,
+    #[clap(long)]
-        help = "Allow multiple primary endpoints running on the same branch. Shouldn't be used normally, but useful for tests."
-    )]
     allow_multiple: bool,
 
-    /// Only allow changing it on creation
+    /// Name of the privileged role for the endpoint.
-    #[clap(long, help = "Name of the privileged role for the endpoint")]
+    // Only allow changing it on creation.
+    #[clap(long)]
     privileged_role_name: Option<String>,
 }
 
+/// Start Postgres. If the endpoint doesn't exist yet, it is created.
 #[derive(clap::Args)]
-#[clap(about = "Start postgres. If the endpoint doesn't exist yet, it is created.")]
 struct EndpointStartCmdArgs {
-    #[clap(help = "Postgres endpoint id")]
+    /// Postgres endpoint ID.
     endpoint_id: String,
+    /// Pageserver ID.
     #[clap(long = "pageserver-id")]
     endpoint_pageserver_id: Option<NodeId>,
-
+    /// Safekeepers membership generation to prefix neon.safekeepers with.
-    #[clap(
+    #[clap(long)]
-        long,
-        help = "Safekeepers membership generation to prefix neon.safekeepers with. Normally neon_local sets it on its own, but this option allows to override. Non zero value forces endpoint to use membership configurations."
-    )]
     safekeepers_generation: Option<u32>,
-    #[clap(
+    /// List of safekeepers endpoint will talk to.
-        long,
+    #[clap(long)]
-        help = "List of safekeepers endpoint will talk to. Normally neon_local chooses them on its own, but this option allows to override."
-    )]
     safekeepers: Option<String>,
-
+    /// Configure the remote extensions storage proxy gateway URL to request for extensions.
-    #[clap(
+    #[clap(long, alias = "remote-ext-config")]
-        long,
-        help = "Configure the remote extensions storage proxy gateway URL to request for extensions.",
-        alias = "remote-ext-config"
-    )]
     remote_ext_base_url: Option<String>,
-
+    /// If set, will create test user `user` and `neondb` database. Requires `update-catalog = true`
-    #[clap(
+    #[clap(long)]
-        long,
-        help = "If set, will create test user `user` and `neondb` database. Requires `update-catalog = true`"
-    )]
     create_test_user: bool,
-
+    /// Allow multiple primary endpoints running on the same branch. Shouldn't be used normally, but
-    #[clap(
+    /// useful for tests.
-        long,
+    #[clap(long)]
-        help = "Allow multiple primary endpoints running on the same branch. Shouldn't be used normally, but useful for tests."
-    )]
     allow_multiple: bool,
-
+    /// Timeout until we fail the command.
-    #[clap(short = 't', long, value_parser= humantime::parse_duration, help = "timeout until we fail the command")]
+    #[clap(short = 't', long, value_parser= humantime::parse_duration)]
     #[arg(default_value = "90s")]
     start_timeout: Duration,
 
-    #[clap(
+    /// Download LFC cache from endpoint storage on endpoint startup
-        long,
+    #[clap(long, default_value = "false")]
-        help = "Download LFC cache from endpoint storage on endpoint startup",
-        default_value = "false"
-    )]
     autoprewarm: bool,
 
-    #[clap(long, help = "Upload LFC cache to endpoint storage periodically")]
+    /// Upload LFC cache to endpoint storage periodically
+    #[clap(long)]
     offload_lfc_interval_seconds: Option<std::num::NonZeroU64>,
 
-    #[clap(
+    /// Run in development mode, skipping VM-specific operations like process termination
-        long,
+    #[clap(long, action = clap::ArgAction::SetTrue)]
-        help = "Run in development mode, skipping VM-specific operations like process termination",
-        action = clap::ArgAction::SetTrue
-    )]
     dev: bool,
 }
 
+/// Reconfigure an endpoint.
 #[derive(clap::Args)]
-#[clap(about = "Reconfigure an endpoint")]
 struct EndpointReconfigureCmdArgs {
-    #[clap(
+    /// Tenant id. Represented as a hexadecimal string 32 symbols length
-        long = "tenant-id",
+    #[clap(long = "tenant-id")]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: Option<TenantId>,
-
+    /// Postgres endpoint ID.
-    #[clap(help = "Postgres endpoint id")]
     endpoint_id: String,
+    /// Pageserver ID.
     #[clap(long = "pageserver-id")]
     endpoint_pageserver_id: Option<NodeId>,
-
     #[clap(long)]
     safekeepers: Option<String>,
 }
 
+/// Refresh the endpoint's configuration by forcing it reload it's spec
 #[derive(clap::Args)]
-#[clap(about = "Refresh the endpoint's configuration by forcing it reload it's spec")]
 struct EndpointRefreshConfigurationArgs {
-    #[clap(help = "Postgres endpoint id")]
+    /// Postgres endpoint id
     endpoint_id: String,
 }
 
+/// Stop an endpoint.
 #[derive(clap::Args)]
-#[clap(about = "Stop an endpoint")]
 struct EndpointStopCmdArgs {
-    #[clap(help = "Postgres endpoint id")]
+    /// Postgres endpoint ID.
     endpoint_id: String,
-
+    /// Also delete data directory (now optional, should be default in future).
-    #[clap(
+    #[clap(long)]
-        long,
-        help = "Also delete data directory (now optional, should be default in future)"
-    )]
     destroy: bool,
 
-    #[clap(long, help = "Postgres shutdown mode")]
+    /// Postgres shutdown mode, passed to `pg_ctl -m <mode>`.
+    #[clap(long)]
     #[clap(default_value = "fast")]
     mode: EndpointTerminateMode,
 }
 
+/// Update the pageservers in the spec file of the compute endpoint
 #[derive(clap::Args)]
-#[clap(about = "Update the pageservers in the spec file of the compute endpoint")]
 struct EndpointUpdatePageserversCmdArgs {
-    #[clap(help = "Postgres endpoint id")]
+    /// Postgres endpoint id
     endpoint_id: String,
 
-    #[clap(short = 'p', long, help = "Specified pageserver id")]
+    /// Specified pageserver id
+    #[clap(short = 'p', long)]
     pageserver_id: Option<NodeId>,
 }
 
+/// Generate a JWT for an endpoint.
 #[derive(clap::Args)]
-#[clap(about = "Generate a JWT for an endpoint")]
 struct EndpointGenerateJwtCmdArgs {
-    #[clap(help = "Postgres endpoint id")]
+    /// Postgres endpoint ID.
     endpoint_id: String,
-
+    /// Scope to generate the JWT with.
-    #[clap(short = 's', long, help = "Scope to generate the JWT with", value_parser = ComputeClaimsScope::from_str)]
+    #[clap(short = 's', long, value_parser = ComputeClaimsScope::from_str)]
     scope: Option<ComputeClaimsScope>,
 }
 
+/// Manage neon_local branch name mappings.
 #[derive(clap::Subcommand)]
-#[clap(about = "Manage neon_local branch name mappings")]
 enum MappingsCmd {
     Map(MappingsMapCmdArgs),
 }
 
+/// Create new mapping which cannot exist already.
 #[derive(clap::Args)]
-#[clap(about = "Create new mapping which cannot exist already")]
 struct MappingsMapCmdArgs {
-    #[clap(
+    /// Tenant ID, as a 32-byte hexadecimal string.
-        long,
+    #[clap(long)]
-        help = "Tenant id. Represented as a hexadecimal string 32 symbols length"
-    )]
     tenant_id: TenantId,
-    #[clap(
+    /// Timeline ID, as a 32-byte hexadecimal string.
-        long,
+    #[clap(long)]
-        help = "Timeline id. Represented as a hexadecimal string 32 symbols length"
-    )]
     timeline_id: TimelineId,
-    #[clap(long, help = "Branch name to give to the timeline")]
+    /// Branch name to give to the timeline.
+    #[clap(long)]
     branch_name: String,
 }
 

docker-compose/compute_wrapper/var/db/postgres/configs/config.json

@@ -120,6 +120,11 @@
                     "value": "host=pageserver port=6400",
                     "vartype": "string"
                 },
+                {
+                    "name": "neon.pageserver_grpc_urls",
+                    "value": "grpc://pageserver:6401/",
+                    "vartype": "string"
+                },
                 {
                     "name": "max_replication_write_lag",
                     "value": "500MB",

docker-compose/pageserver_config/pageserver.toml

@@ -1,6 +1,7 @@
 broker_endpoint='http://storage_broker:50051'
 pg_distrib_dir='/usr/local/'
 listen_pg_addr='0.0.0.0:6400'
+listen_grpc_addr='0.0.0.0:6401'
 listen_http_addr='0.0.0.0:9898'
 remote_storage={ endpoint='http://minio:9000', bucket_name='neon', bucket_region='eu-north-1', prefix_in_bucket='/pageserver' }
 control_plane_api='http://0.0.0.0:6666' # No storage controller in docker compose, specify a junk address

docs/rfcs/2025-07-07-node-deletion-api-improvement.md

@@ -0,0 +1,246 @@
+# Node deletion API improvement
+
+Created on 2025-07-07
+Implemented on _TBD_
+
+## Summary
+
+This RFC describes improvements to the storage controller API for gracefully deleting pageserver
+nodes.
+
+## Motivation
+
+The basic node deletion API introduced in [#8226](https://github.com/neondatabase/neon/issues/8333)
+has several limitations:
+
+- Deleted nodes can re-add themselves if they restart (e.g., a flaky node that keeps restarting and
+we cannot reach via SSH to stop the pageserver). This issue has been resolved by tombstone
+mechanism in [#12036](https://github.com/neondatabase/neon/issues/12036)
+- Process of node deletion is not graceful, i.e. it just imitates a node failure
+
+In this context, "graceful" node deletion means that users do not experience any disruption or
+negative effects, provided the system remains in a healthy state (i.e., the remaining pageservers
+can handle the workload and all requirements are met). To achieve this, the system must perform
+live migration of all tenant shards from the node being deleted while the node is still running
+and continue processing all incoming requests. The node is removed only after all tenant shards
+have been safely migrated.
+
+Although live migrations can be achieved with the drain functionality, it leads to incorrect shard
+placement, such as not matching availability zones. This results in unnecessary work to optimize
+the placement that was just recently performed.
+
+If we delete a node before its tenant shards are fully moved, the new node won't have all the
+needed data (e.g. heatmaps) ready. This means user requests to the new node will be much slower at
+first. If there are many tenant shards, this slowdown affects a huge amount of users.
+
+Graceful node deletion is more complicated and can introduce new issues. It takes longer because
+live migration of each tenant shard can last several minutes. Using non-blocking accessors may
+also cause deletion to wait if other processes are holding inner state lock. It also gets trickier
+because we need to handle other requests, like drain and fill, at the same time.
+
+## Impacted components (e.g. pageserver, safekeeper, console, etc)
+
+- storage controller
+- pageserver (indirectly)
+
+## Proposed implementation
+
+### Tombstones
+
+To resolve the problem of deleted nodes re-adding themselves, a tombstone mechanism was introduced
+as part of the node stored information. Each node has a separate `NodeLifecycle` field with two
+possible states: `Active` and `Deleted`. When node deletion completes, the database row is not
+deleted but instead has its `NodeLifecycle` column switched to `Deleted`. Nodes with `Deleted`
+lifecycle are treated as if the row is absent for most handlers, with several exceptions: reattach
+and register functionality must be aware of tombstones. Additionally, new debug handlers are
+available for listing and deleting tombstones via the `/debug/v1/tombstone` path.
+
+### Gracefulness
+
+The problem of making node deletion graceful is complex and involves several challenges:
+
+- **Cancellable**: The operation must be cancellable to allow administrators to abort the process
+if needed, e.g. if run by mistake.
+- **Non-blocking**: We don't want to block deployment operations like draining/filling on the node
+deletion process. We need clear policies for handling concurrent operations: what happens when a
+drain/fill request arrives while deletion is in progress, and what happens when a delete request
+arrives while drain/fill is in progress.
+- **Persistent**: If the storage controller restarts during this long-running operation, we must
+preserve progress and automatically resume the deletion process after the storage controller
+restarts.
+- **Migrated correctly**: We cannot simply use the existing drain mechanism for nodes scheduled
+for deletion, as this would move shards to irrelevant locations. The drain process expects the
+node to return, so it only moves shards to backup locations, not to their preferred AZs. It also
+leaves secondary locations unmoved. This could result in unnecessary load on the storage
+controller and inefficient resource utilization.
+- **Force option**: Administrators need the ability to force immediate, non-graceful deletion when
+time constraints or emergency situations require it, bypassing the normal graceful migration
+process.
+
+See below for a detailed breakdown of the proposed changes and mechanisms.
+
+#### Node lifecycle
+
+New `NodeLifecycle` enum and a matching database field with these values:
+- `Active`: The normal state. All operations are allowed.
+- `ScheduledForDeletion`: The node is marked to be deleted soon. Deletion may be in progress or
+will happen later, but the node will eventually be removed. All operations are allowed.
+- `Deleted`: The node is fully deleted. No operations are allowed, and the node cannot be brought
+back. The only action left is to remove its record from the database. Any attempt to register a
+node in this state will fail.
+
+This state persists across storage controller restarts.
+
+**State transition**
+```
+        +--------------------+
+    +---|       Active       |<---------------------+
+    |   +--------------------+                      |
+    |                     ^                         |
+    | start_node_delete   | cancel_node_delete      |
+    v                     |                         |
+  +----------------------------------+              |
+  |       ScheduledForDeletion       |              |
+  +----------------------------------+              |
+       |                                            |
+       |                              node_register |
+       |                                            |
+       | delete_node (at the finish)                |
+       |                                            |
+       v                                            |
+  +---------+         tombstone_delete        +----------+
+  | Deleted |-------------------------------->|  no row  |
+  +---------+                                 +----------+
+```
+
+#### NodeSchedulingPolicy::Deleting
+
+A `Deleting` variant to the `NodeSchedulingPolicy` enum. This means the deletion function is
+running for the node right now. Only one node can have the `Deleting` policy at a time.
+
+The `NodeSchedulingPolicy::Deleting` state is persisted in the database. However, after a storage
+controller restart, any node previously marked as `Deleting` will have its scheduling policy reset
+to `Pause`. The policy will only transition back to `Deleting` when the deletion operation is
+actively started again, as triggered by the node's `NodeLifecycle::ScheduledForDeletion` state.
+
+`NodeSchedulingPolicy` transition details:
+1. When `node_delete` begins, set the policy to `NodeSchedulingPolicy::Deleting`.
+2. If `node_delete` is cancelled (for example, due to a concurrent drain operation), revert the
+policy to its previous value. The policy is persisted in storcon DB.
+3. After `node_delete` completes, the final value of the scheduling policy is irrelevant, since
+`NodeLifecycle::Deleted` prevents any further access to this field.
+
+The deletion process cannot be initiated for nodes currently undergoing deployment-related
+operations (`Draining`, `Filling`, or `PauseForRestart` policies). Deletion will only be triggered
+once the node transitions to either the `Active` or `Pause` state.
+
+#### OperationTracker
+
+A replacement for `Option<OperationHandler> ongoing_operation`, the `OperationTracker` is a
+dedicated service state object responsible for managing all long-running node operations (drain,
+fill, delete) with robust concurrency control.
+
+Key responsibilities:
+- Orchestrates the execution of operations
+- Supports cancellation of currently running operations
+- Enforces operation constraints, e.g. allowing only single drain/fill operation at a time
+- Persists deletion state, enabling recovery of pending deletions across restarts
+- Ensures thread safety across concurrent requests
+
+#### Attached tenant shard processing
+
+When deleting a node, handle each attached tenant shard as follows:
+
+1. Pick the best node to become the new attached (the candidate).
+2. If the candidate already has this shard as a secondary:
+    - Create a new secondary for the shard on another suitable node.
+   Otherwise:
+    - Create a secondary for the shard on the candidate node.
+3. Wait until all secondaries are ready and pre-warmed.
+4. Promote the candidate's secondary to attached.
+5. Remove the secondary from the node being deleted.
+
+This process safely moves all attached shards before deleting the node.
+
+#### Secondary tenant shard processing
+
+When deleting a node, handle each secondary tenant shard as follows:
+
+1. Choose the best node to become the new secondary.
+2. Create a secondary for the shard on that node.
+3. Wait until the new secondary is ready.
+4. Remove the secondary from the node being deleted.
+
+This ensures all secondary shards are safely moved before deleting the node.
+
+### Reliability, failure modes and corner cases
+
+In case of a storage controller failure and following restart, the system behavior depends on the
+`NodeLifecycle` state:
+
+- If `NodeLifecycle` is `Active`: No action is taken for this node.
+- If `NodeLifecycle` is `Deleted`: The node will not be re-added.
+- If `NodeLifecycle` is `ScheduledForDeletion`: A deletion background task will be launched for
+this node.
+
+In case of a pageserver node failure during deletion, the behavior depends on the `force` flag:
+- If `force` is set: The node deletion will proceed regardless of the node's availability.
+- If `force` is not set: The deletion will be retried a limited number of times. If the node
+remains unavailable, the deletion process will pause and automatically resume when the node
+becomes healthy again.
+
+### Operations concurrency
+
+The following sections describe the behavior when different types of requests arrive at the storage
+controller and how they interact with ongoing operations.
+
+#### Delete request
+
+Handler: `PUT /control/v1/node/:node_id/delete`
+
+1. If node lifecycle is `NodeLifecycle::ScheduledForDeletion`:
+    - Return `200 OK`: there is already an ongoing deletion request for this node
+2. Update & persist lifecycle to `NodeLifecycle::ScheduledForDeletion`
+3. Persist current scheduling policy
+4. If there is no active operation (drain/fill/delete):
+    - Run deletion process for this node
+
+#### Cancel delete request
+
+Handler: `DELETE /control/v1/node/:node_id/delete`
+
+1. If node lifecycle is not `NodeLifecycle::ScheduledForDeletion`:
+    - Return `404 Not Found`: there is no current deletion request for this node
+2. If the active operation is deleting this node, cancel it
+3. Update & persist lifecycle to `NodeLifecycle::Active`
+4. Restore the last scheduling policy from persistence
+
+#### Drain/fill request
+
+1. If there are already ongoing drain/fill processes:
+    - Return `409 Conflict`: queueing of drain/fill processes is not supported
+2. If there is an ongoing delete process:
+    - Cancel it and wait until it is cancelled
+3. Run the drain/fill process
+4. After the drain/fill process is cancelled or finished:
+    - Try to find another candidate to delete and run the deletion process for that node
+
+#### Drain/fill cancel request
+
+1. If the active operation is not the related process:
+    - Return `400 Bad Request`: cancellation request is incorrect, operations are not the same
+2. Cancel the active operation
+3. Try to find another candidate to delete and run the deletion process for that node
+
+## Definition of Done
+
+- [x] Fix flaky node scenario and introduce related debug handlers
+- [ ] Node deletion intent is persistent - a node will be eventually deleted after a deletion
+request regardless of draining/filling requests and restarts
+- [ ] Node deletion can be graceful - deletion completes only after moving all tenant shards to
+recommended locations
+- [ ] Deploying does not break due to long deletions - drain/fill operations override deletion
+process and deletion resumes after drain/fill completes
+- [ ] `force` flag is implemented and provides fast, failure-tolerant node removal (e.g., when a
+pageserver node does not respond)
+- [ ] Legacy delete handler code is removed from storage_controller, test_runner, and storcon_cli

libs/compute_api/src/responses.rs

@@ -68,11 +68,15 @@ pub enum LfcPrewarmState {
     /// We tried to fetch the corresponding LFC state from the endpoint storage,
     /// but received `Not Found 404`. This should normally happen only during the
     /// first endpoint start after creation with `autoprewarm: true`.
+    /// This may also happen if LFC is turned off or not initialized
     ///
     /// During the orchestrated prewarm via API, when a caller explicitly
     /// provides the LFC state key to prewarm from, it's the caller responsibility
     /// to handle this status as an error state in this case.
     Skipped,
+    /// LFC prewarm was cancelled. Some pages in LFC cache may be prewarmed if query
+    /// has started working before cancellation
+    Cancelled,
 }
 
 impl Display for LfcPrewarmState {
@@ -83,6 +87,7 @@ impl Display for LfcPrewarmState {
             LfcPrewarmState::Completed => f.write_str("Completed"),
             LfcPrewarmState::Skipped => f.write_str("Skipped"),
             LfcPrewarmState::Failed { error } => write!(f, "Error({error})"),
+            LfcPrewarmState::Cancelled => f.write_str("Cancelled"),
         }
     }
 }
@@ -97,6 +102,7 @@ pub enum LfcOffloadState {
     Failed {
         error: String,
     },
+    Skipped,
 }
 
 #[derive(Serialize, Debug, Clone, PartialEq)]

libs/neon-shmem/Cargo.toml

@@ -6,15 +6,26 @@ license.workspace = true
 
 [dependencies]
 thiserror.workspace = true
-nix.workspace=true
+nix.workspace = true
 workspace_hack = { version = "0.1", path = "../../workspace_hack" }
 libc.workspace = true
 lock_api.workspace = true
 rustc-hash.workspace = true
 
+[dev-dependencies]
+criterion = { workspace = true, features = ["html_reports"] }
+rand = "0.9"
+rand_distr = "0.5.1"
+xxhash-rust = { version = "0.8.15", features = ["xxh3"] }
+ahash.workspace = true
+twox-hash = { version = "2.1.1" }
+seahash = "4.1.0"
+hashbrown = { git = "https://github.com/quantumish/hashbrown.git", rev = "6610e6d" }
+
+
 [target.'cfg(target_os = "macos")'.dependencies]
 tempfile = "3.14.0"
 
-[dev-dependencies]
+[[bench]]
-rand.workspace = true
+name = "hmap_resize"
-rand_distr = "0.5.1"
+harness = false

libs/neon-shmem/benches/hmap_resize.rs

@@ -0,0 +1,330 @@
+use criterion::{BatchSize, BenchmarkId, Criterion, criterion_group, criterion_main};
+use neon_shmem::hash::HashMapAccess;
+use neon_shmem::hash::HashMapInit;
+use neon_shmem::hash::entry::Entry;
+use rand::distr::{Distribution, StandardUniform};
+use rand::prelude::*;
+use std::default::Default;
+use std::hash::BuildHasher;
+
+// Taken from bindings to C code
+
+#[derive(Clone, Debug, Hash, Eq, PartialEq)]
+#[repr(C)]
+pub struct FileCacheKey {
+    pub _spc_id: u32,
+    pub _db_id: u32,
+    pub _rel_number: u32,
+    pub _fork_num: u32,
+    pub _block_num: u32,
+}
+
+impl Distribution<FileCacheKey> for StandardUniform {
+    // questionable, but doesn't need to be good randomness
+    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> FileCacheKey {
+        FileCacheKey {
+            _spc_id: rng.random(),
+            _db_id: rng.random(),
+            _rel_number: rng.random(),
+            _fork_num: rng.random(),
+            _block_num: rng.random(),
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+#[repr(C)]
+pub struct FileCacheEntry {
+    pub _offset: u32,
+    pub _access_count: u32,
+    pub _prev: *mut FileCacheEntry,
+    pub _next: *mut FileCacheEntry,
+    pub _state: [u32; 8],
+}
+
+impl FileCacheEntry {
+    fn dummy() -> Self {
+        Self {
+            _offset: 0,
+            _access_count: 0,
+            _prev: std::ptr::null_mut(),
+            _next: std::ptr::null_mut(),
+            _state: [0; 8],
+        }
+    }
+}
+
+// Utilities for applying operations.
+
+#[derive(Clone, Debug)]
+struct TestOp<K, V>(K, Option<V>);
+
+fn apply_op<K: Clone + std::hash::Hash + Eq, V, S: std::hash::BuildHasher>(
+    op: TestOp<K, V>,
+    map: &mut HashMapAccess<K, V, S>,
+) {
+    let entry = map.entry(op.0);
+
+    match op.1 {
+        Some(new) => match entry {
+            Entry::Occupied(mut e) => Some(e.insert(new)),
+            Entry::Vacant(e) => {
+                _ = e.insert(new).unwrap();
+                None
+            }
+        },
+        None => match entry {
+            Entry::Occupied(e) => Some(e.remove()),
+            Entry::Vacant(_) => None,
+        },
+    };
+}
+
+// Hash utilities
+
+struct SeaRandomState {
+    k1: u64,
+    k2: u64,
+    k3: u64,
+    k4: u64,
+}
+
+impl std::hash::BuildHasher for SeaRandomState {
+    type Hasher = seahash::SeaHasher;
+
+    fn build_hasher(&self) -> Self::Hasher {
+        seahash::SeaHasher::with_seeds(self.k1, self.k2, self.k3, self.k4)
+    }
+}
+
+impl SeaRandomState {
+    fn new() -> Self {
+        let mut rng = rand::rng();
+        Self {
+            k1: rng.random(),
+            k2: rng.random(),
+            k3: rng.random(),
+            k4: rng.random(),
+        }
+    }
+}
+
+fn small_benchs(c: &mut Criterion) {
+    let mut group = c.benchmark_group("Small maps");
+    group.sample_size(10);
+
+    group.bench_function("small_rehash", |b| {
+        let ideal_filled = 4_000_000;
+        let size = 5_000_000;
+        let mut writer = HashMapInit::new_resizeable(size, size * 2).attach_writer();
+        let mut rng = rand::rng();
+        while writer.get_num_buckets_in_use() < ideal_filled as usize {
+            let key: FileCacheKey = rng.random();
+            let val = FileCacheEntry::dummy();
+            apply_op(TestOp(key, Some(val)), &mut writer);
+        }
+        b.iter(|| writer.shuffle());
+    });
+
+    group.bench_function("small_rehash_xxhash", |b| {
+        let ideal_filled = 4_000_000;
+        let size = 5_000_000;
+        let mut writer = HashMapInit::new_resizeable(size, size * 2)
+            .with_hasher(twox_hash::xxhash64::RandomState::default())
+            .attach_writer();
+        let mut rng = rand::rng();
+        while writer.get_num_buckets_in_use() < ideal_filled as usize {
+            let key: FileCacheKey = rng.random();
+            let val = FileCacheEntry::dummy();
+            apply_op(TestOp(key, Some(val)), &mut writer);
+        }
+        b.iter(|| writer.shuffle());
+    });
+
+    group.bench_function("small_rehash_ahash", |b| {
+        let ideal_filled = 4_000_000;
+        let size = 5_000_000;
+        let mut writer = HashMapInit::new_resizeable(size, size * 2)
+            .with_hasher(ahash::RandomState::default())
+            .attach_writer();
+        let mut rng = rand::rng();
+        while writer.get_num_buckets_in_use() < ideal_filled as usize {
+            let key: FileCacheKey = rng.random();
+            let val = FileCacheEntry::dummy();
+            apply_op(TestOp(key, Some(val)), &mut writer);
+        }
+        b.iter(|| writer.shuffle());
+    });
+
+    group.bench_function("small_rehash_seahash", |b| {
+        let ideal_filled = 4_000_000;
+        let size = 5_000_000;
+        let mut writer = HashMapInit::new_resizeable(size, size * 2)
+            .with_hasher(SeaRandomState::new())
+            .attach_writer();
+        let mut rng = rand::rng();
+        while writer.get_num_buckets_in_use() < ideal_filled as usize {
+            let key: FileCacheKey = rng.random();
+            let val = FileCacheEntry::dummy();
+            apply_op(TestOp(key, Some(val)), &mut writer);
+        }
+        b.iter(|| writer.shuffle());
+    });
+
+    group.finish();
+}
+
+fn real_benchs(c: &mut Criterion) {
+    let mut group = c.benchmark_group("Realistic workloads");
+    group.sample_size(10);
+    group.bench_function("real_bulk_insert", |b| {
+        let size = 125_000_000;
+        let ideal_filled = 100_000_000;
+        let mut rng = rand::rng();
+        b.iter_batched(
+            || HashMapInit::new_resizeable(size, size * 2).attach_writer(),
+            |writer| {
+                for _ in 0..ideal_filled {
+                    let key: FileCacheKey = rng.random();
+                    let val = FileCacheEntry::dummy();
+                    let entry = writer.entry(key);
+                    match entry {
+                        Entry::Occupied(mut e) => {
+                            std::hint::black_box(e.insert(val));
+                        }
+                        Entry::Vacant(e) => {
+                            let _ = std::hint::black_box(e.insert(val).unwrap());
+                        }
+                    }
+                }
+            },
+            BatchSize::SmallInput,
+        )
+    });
+
+    group.bench_function("real_rehash", |b| {
+        let size = 125_000_000;
+        let ideal_filled = 100_000_000;
+        let mut writer = HashMapInit::new_resizeable(size, size).attach_writer();
+        let mut rng = rand::rng();
+        while writer.get_num_buckets_in_use() < ideal_filled {
+            let key: FileCacheKey = rng.random();
+            let val = FileCacheEntry::dummy();
+            apply_op(TestOp(key, Some(val)), &mut writer);
+        }
+        b.iter(|| writer.shuffle());
+    });
+
+    group.bench_function("real_rehash_hashbrown", |b| {
+        let size = 125_000_000;
+        let ideal_filled = 100_000_000;
+        let mut writer = hashbrown::raw::RawTable::new();
+        let mut rng = rand::rng();
+        let hasher = rustc_hash::FxBuildHasher;
+        unsafe {
+            writer
+                .resize(
+                    size,
+                    |(k, _)| hasher.hash_one(k),
+                    hashbrown::raw::Fallibility::Infallible,
+                )
+                .unwrap();
+        }
+        while writer.len() < ideal_filled as usize {
+            let key: FileCacheKey = rng.random();
+            let val = FileCacheEntry::dummy();
+            writer.insert(hasher.hash_one(&key), (key, val), |(k, _)| {
+                hasher.hash_one(k)
+            });
+        }
+        b.iter(|| unsafe {
+            writer.table.rehash_in_place(
+                &|table, index| {
+                    hasher.hash_one(
+                        &table
+                            .bucket::<(FileCacheKey, FileCacheEntry)>(index)
+                            .as_ref()
+                            .0,
+                    )
+                },
+                std::mem::size_of::<(FileCacheKey, FileCacheEntry)>(),
+                if std::mem::needs_drop::<(FileCacheKey, FileCacheEntry)>() {
+                    Some(|ptr| std::ptr::drop_in_place(ptr as *mut (FileCacheKey, FileCacheEntry)))
+                } else {
+                    None
+                },
+            )
+        });
+    });
+
+    for elems in [2, 4, 8, 16, 32, 64, 96, 112] {
+        group.bench_with_input(
+            BenchmarkId::new("real_rehash_varied", elems),
+            &elems,
+            |b, &size| {
+                let ideal_filled = size * 1_000_000;
+                let size = 125_000_000;
+                let mut writer = HashMapInit::new_resizeable(size, size).attach_writer();
+                let mut rng = rand::rng();
+                while writer.get_num_buckets_in_use() < ideal_filled as usize {
+                    let key: FileCacheKey = rng.random();
+                    let val = FileCacheEntry::dummy();
+                    apply_op(TestOp(key, Some(val)), &mut writer);
+                }
+                b.iter(|| writer.shuffle());
+            },
+        );
+        group.bench_with_input(
+            BenchmarkId::new("real_rehash_varied_hashbrown", elems),
+            &elems,
+            |b, &size| {
+                let ideal_filled = size * 1_000_000;
+                let size = 125_000_000;
+                let mut writer = hashbrown::raw::RawTable::new();
+                let mut rng = rand::rng();
+                let hasher = rustc_hash::FxBuildHasher;
+                unsafe {
+                    writer
+                        .resize(
+                            size,
+                            |(k, _)| hasher.hash_one(k),
+                            hashbrown::raw::Fallibility::Infallible,
+                        )
+                        .unwrap();
+                }
+                while writer.len() < ideal_filled as usize {
+                    let key: FileCacheKey = rng.random();
+                    let val = FileCacheEntry::dummy();
+                    writer.insert(hasher.hash_one(&key), (key, val), |(k, _)| {
+                        hasher.hash_one(k)
+                    });
+                }
+                b.iter(|| unsafe {
+                    writer.table.rehash_in_place(
+                        &|table, index| {
+                            hasher.hash_one(
+                                &table
+                                    .bucket::<(FileCacheKey, FileCacheEntry)>(index)
+                                    .as_ref()
+                                    .0,
+                            )
+                        },
+                        std::mem::size_of::<(FileCacheKey, FileCacheEntry)>(),
+                        if std::mem::needs_drop::<(FileCacheKey, FileCacheEntry)>() {
+                            Some(|ptr| {
+                                std::ptr::drop_in_place(ptr as *mut (FileCacheKey, FileCacheEntry))
+                            })
+                        } else {
+                            None
+                        },
+                    )
+                });
+            },
+        );
+    }
+
+    group.finish();
+}
+
+criterion_group!(benches, small_benchs, real_benchs);
+criterion_main!(benches);

libs/neon-shmem/src/hash.rs

@@ -16,6 +16,7 @@
 //!
 //! Concurrency is managed very simply: the entire map is guarded by one shared-memory RwLock.
 
+use std::fmt::Debug;
 use std::hash::{BuildHasher, Hash};
 use std::mem::MaybeUninit;
 
@@ -56,6 +57,22 @@ pub struct HashMapInit<'a, K, V, S = rustc_hash::FxBuildHasher> {
     num_buckets: u32,
 }
 
+impl<'a, K, V, S> Debug for HashMapInit<'a, K, V, S>
+where
+    K: Debug,
+    V: Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("HashMapInit")
+            .field("shmem_handle", &self.shmem_handle)
+            .field("shared_ptr", &self.shared_ptr)
+            .field("shared_size", &self.shared_size)
+            // .field("hasher", &self.hasher)
+            .field("num_buckets", &self.num_buckets)
+            .finish()
+    }
+}
+
 /// This is a per-process handle to a hash table that (possibly) lives in shared memory.
 /// If a child process is launched with fork(), the child process should
 /// get its own HashMapAccess by calling HashMapInit::attach_writer/reader().
@@ -71,6 +88,20 @@ pub struct HashMapAccess<'a, K, V, S = rustc_hash::FxBuildHasher> {
 unsafe impl<K: Sync, V: Sync, S> Sync for HashMapAccess<'_, K, V, S> {}
 unsafe impl<K: Send, V: Send, S> Send for HashMapAccess<'_, K, V, S> {}
 
+impl<'a, K, V, S> Debug for HashMapAccess<'a, K, V, S>
+where
+    K: Debug,
+    V: Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("HashMapAccess")
+            .field("shmem_handle", &self.shmem_handle)
+            .field("shared_ptr", &self.shared_ptr)
+            // .field("hasher", &self.hasher)
+            .finish()
+    }
+}
+
 impl<'a, K: Clone + Hash + Eq, V, S> HashMapInit<'a, K, V, S> {
     /// Change the 'hasher' used by the hash table.
     ///
@@ -298,7 +329,7 @@ where
 
     /// Get a reference to the entry containing a key.
     ///
-    /// NB: THis takes a write lock as there's no way to distinguish whether the intention
+    /// NB: This takes a write lock as there's no way to distinguish whether the intention
     /// is to use the entry for reading or for writing in advance.
     pub fn entry(&self, key: K) -> Entry<'a, '_, K, V> {
         let hash = self.get_hash_value(&key);

libs/neon-shmem/src/hash/core.rs

@@ -1,5 +1,6 @@
 //! Simple hash table with chaining.
 
+use std::fmt::Debug;
 use std::hash::Hash;
 use std::mem::MaybeUninit;
 
@@ -17,6 +18,19 @@ pub(crate) struct Bucket<K, V> {
     pub(crate) inner: Option<(K, V)>,
 }
 
+impl<K, V> Debug for Bucket<K, V>
+where
+    K: Debug,
+    V: Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Bucket")
+            .field("next", &self.next)
+            .field("inner", &self.inner)
+            .finish()
+    }
+}
+
 /// Core hash table implementation.
 pub(crate) struct CoreHashMap<'a, K, V> {
     /// Dictionary used to map hashes to bucket indices.
@@ -31,6 +45,22 @@ pub(crate) struct CoreHashMap<'a, K, V> {
     pub(crate) buckets_in_use: u32,
 }
 
+impl<'a, K, V> Debug for CoreHashMap<'a, K, V>
+where
+    K: Debug,
+    V: Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CoreHashMap")
+            .field("dictionary", &self.dictionary)
+            .field("buckets", &self.buckets)
+            .field("free_head", &self.free_head)
+            .field("alloc_limit", &self.alloc_limit)
+            .field("buckets_in_use", &self.buckets_in_use)
+            .finish()
+    }
+}
+
 /// Error for when there are no empty buckets left but one is needed.
 #[derive(Debug, PartialEq)]
 pub struct FullError;

libs/neon-shmem/src/hash/entry.rs

@@ -61,6 +61,10 @@ impl<K, V> OccupiedEntry<'_, '_, K, V> {
     ///
     /// This may result in multiple bucket accesses if the entry was obtained by index as the
     /// previous chain entry needs to be discovered in this case.
+    ///
+    /// # Panics
+    /// Panics if the `prev_pos` field is equal to [`PrevPos::Unknown`]. In practice, this means
+    /// the entry was obtained via calling something like [`super::HashMapAccess::entry_at_bucket`].
     pub fn remove(mut self) -> V {
         // If this bucket was queried by index, go ahead and follow its chain from the start.
         let prev = if let PrevPos::Unknown(hash) = self.prev_pos {

libs/neon-shmem/src/shmem.rs

@@ -21,6 +21,7 @@ use nix::unistd::ftruncate as nix_ftruncate;
 /// the underlying file is resized. Do not access the area beyond the current size. Currently, that
 /// will cause the file to be expanded, but we might use `mprotect()` etc. to enforce that in the
 /// future.
+#[derive(Debug)]
 pub struct ShmemHandle {
     /// memfd file descriptor
     fd: OwnedFd,
@@ -35,6 +36,7 @@ pub struct ShmemHandle {
 }
 
 /// This is stored at the beginning in the shared memory area.
+#[derive(Debug)]
 struct SharedStruct {
     max_size: usize,
 

libs/utils/src/lsn.rs

@@ -310,6 +310,11 @@ impl AtomicLsn {
         }
     }
 
+    /// Consumes the atomic and returns the contained value.
+    pub const fn into_inner(self) -> Lsn {
+        Lsn(self.inner.into_inner())
+    }
+
     /// Atomically retrieve the `Lsn` value from memory.
     pub fn load(&self) -> Lsn {
         Lsn(self.inner.load(Ordering::Acquire))

libs/walproposer/src/api_bindings.rs

@@ -341,6 +341,34 @@ extern "C-unwind" fn log_internal(
     }
 }
 
+/* BEGIN_HADRON */
+extern "C" fn reset_safekeeper_statuses_for_metrics(wp: *mut WalProposer, num_safekeepers: u32) {
+    unsafe {
+        let callback_data = (*(*wp).config).callback_data;
+        let api = callback_data as *mut Box<dyn ApiImpl>;
+        if api.is_null() {
+            return;
+        }
+        (*api).reset_safekeeper_statuses_for_metrics(&mut (*wp), num_safekeepers);
+    }
+}
+
+extern "C" fn update_safekeeper_status_for_metrics(
+    wp: *mut WalProposer,
+    sk_index: u32,
+    status: u8,
+) {
+    unsafe {
+        let callback_data = (*(*wp).config).callback_data;
+        let api = callback_data as *mut Box<dyn ApiImpl>;
+        if api.is_null() {
+            return;
+        }
+        (*api).update_safekeeper_status_for_metrics(&mut (*wp), sk_index, status);
+    }
+}
+/* END_HADRON */
+
 #[derive(Debug, PartialEq)]
 pub enum Level {
     Debug5,
@@ -414,6 +442,10 @@ pub(crate) fn create_api() -> walproposer_api {
         finish_sync_safekeepers: Some(finish_sync_safekeepers),
         process_safekeeper_feedback: Some(process_safekeeper_feedback),
         log_internal: Some(log_internal),
+        /* BEGIN_HADRON */
+        reset_safekeeper_statuses_for_metrics: Some(reset_safekeeper_statuses_for_metrics),
+        update_safekeeper_status_for_metrics: Some(update_safekeeper_status_for_metrics),
+        /* END_HADRON */
     }
 }
 
@@ -451,6 +483,8 @@ pub fn empty_shmem() -> crate::bindings::WalproposerShmemState {
         replica_promote: false,
         min_ps_feedback: empty_feedback,
         wal_rate_limiter: empty_wal_rate_limiter,
+        num_safekeepers: 0,
+        safekeeper_status: [0; 32],
     }
 }
 

libs/walproposer/src/walproposer.rs

@@ -159,6 +159,21 @@ pub trait ApiImpl {
     fn after_election(&self, _wp: &mut WalProposer) {
         todo!()
     }
+
+    /* BEGIN_HADRON */
+    fn reset_safekeeper_statuses_for_metrics(&self, _wp: &mut WalProposer, _num_safekeepers: u32) {
+        // Do nothing for testing purposes.
+    }
+
+    fn update_safekeeper_status_for_metrics(
+        &self,
+        _wp: &mut WalProposer,
+        _sk_index: u32,
+        _status: u8,
+    ) {
+        // Do nothing for testing purposes.
+    }
+    /* END_HADRON */
 }
 
 #[derive(Debug)]

pageserver/Cargo.toml

@@ -54,6 +54,7 @@ pageserver_api.workspace = true
 pageserver_client.workspace = true # for ResponseErrorMessageExt TOOD refactor that
 pageserver_compaction.workspace = true
 pageserver_page_api.workspace = true
+peekable.workspace = true
 pem.workspace = true
 pin-project-lite.workspace = true
 postgres_backend.workspace = true
@@ -66,6 +67,7 @@ postgres-types.workspace = true
 posthog_client_lite.workspace = true
 pprof.workspace = true
 pq_proto.workspace = true
+prost.workspace = true
 rand.workspace = true
 range-set-blaze = { version = "0.1.16", features = ["alloc"] }
 regex.workspace = true

pageserver/client_grpc/src/lib.rs

@@ -3,3 +3,4 @@ mod pool;
 mod retry;
 
 pub use client::{PageserverClient, ShardSpec};
+pub use pageserver_api::shard::ShardStripeSize; // used in ShardSpec

pageserver/page_api/src/model.rs

@@ -33,6 +33,8 @@ pub enum ProtocolError {
     Invalid(&'static str, String),
     #[error("required field '{0}' is missing")]
     Missing(&'static str),
+    #[error("invalid combination of not_modified_lsn '{0}' and request_lsn '{1}'")]
+    InvalidLsns(Lsn, Lsn),
 }
 
 impl ProtocolError {
@@ -85,9 +87,9 @@ impl TryFrom<proto::ReadLsn> for ReadLsn {
             return Err(ProtocolError::invalid("request_lsn", pb.request_lsn));
         }
         if pb.not_modified_since_lsn > pb.request_lsn {
-            return Err(ProtocolError::invalid(
+            return Err(ProtocolError::InvalidLsns(
-                "not_modified_since_lsn",
+                Lsn(pb.not_modified_since_lsn),
-                pb.not_modified_since_lsn,
+                Lsn(pb.request_lsn),
             ));
         }
         Ok(Self {

pageserver/pagebench/Cargo.toml

@@ -25,6 +25,9 @@ tracing.workspace = true
 tokio.workspace = true
 tokio-stream.workspace = true
 tokio-util.workspace = true
+axum.workspace = true
+http.workspace = true
+metrics.workspace = true
 tonic.workspace = true
 url.workspace = true
 

pageserver/pagebench/src/cmd/getpage_latest_lsn.rs

@@ -34,6 +34,10 @@ use crate::util::{request_stats, tokio_thread_local_stats};
 /// GetPage@LatestLSN, uniformly distributed across the compute-accessible keyspace.
 #[derive(clap::Parser)]
 pub(crate) struct Args {
+    #[clap(long, default_value = "false")]
+    grpc: bool,
+    #[clap(long, default_value = "false")]
+    grpc_stream: bool,
     #[clap(long, default_value = "http://localhost:9898")]
     mgmt_api_endpoint: String,
     /// Pageserver connection string. Supports postgresql:// and grpc:// protocols.
@@ -78,6 +82,9 @@ pub(crate) struct Args {
     #[clap(long)]
     set_io_mode: Option<pageserver_api::models::virtual_file::IoMode>,
 
+    #[clap(long)]
+    only_relnode: Option<u32>,
+
     /// Queue depth generated in each client.
     #[clap(long, default_value = "1")]
     queue_depth: NonZeroUsize,
@@ -92,10 +99,31 @@ pub(crate) struct Args {
     #[clap(long, default_value = "1")]
     batch_size: NonZeroUsize,
 
-    #[clap(long)]
-    only_relnode: Option<u32>,
-
     targets: Option<Vec<TenantTimelineId>>,
+
+    #[clap(long, default_value = "100")]
+    pool_max_consumers: NonZeroUsize,
+
+    #[clap(long, default_value = "5")]
+    pool_error_threshold: NonZeroUsize,
+
+    #[clap(long, default_value = "5000")]
+    pool_connect_timeout: NonZeroUsize,
+
+    #[clap(long, default_value = "1000")]
+    pool_connect_backoff: NonZeroUsize,
+
+    #[clap(long, default_value = "60000")]
+    pool_max_idle_duration: NonZeroUsize,
+
+    #[clap(long, default_value = "0")]
+    max_delay_ms: usize,
+
+    #[clap(long, default_value = "0")]
+    percent_drops: usize,
+
+    #[clap(long, default_value = "0")]
+    percent_hangs: usize,
 }
 
 /// State shared by all clients
@@ -152,7 +180,6 @@ pub(crate) fn main(args: Args) -> anyhow::Result<()> {
         main_impl(args, thread_local_stats)
     })
 }
-
 async fn main_impl(
     args: Args,
     all_thread_local_stats: AllThreadLocalStats<request_stats::Stats>,
@@ -317,6 +344,7 @@ async fn main_impl(
     let rps_period = args
         .per_client_rate
         .map(|rps_limit| Duration::from_secs_f64(1.0 / (rps_limit as f64)));
+
     let make_worker: &dyn Fn(WorkerId) -> Pin<Box<dyn Send + Future<Output = ()>>> = &|worker_id| {
         let ss = shared_state.clone();
         let cancel = cancel.clone();

pageserver/src/page_service.rs

@@ -453,6 +453,7 @@ impl TimelineHandles {
             handles: Default::default(),
         }
     }
+
     async fn get(
         &mut self,
         tenant_id: TenantId,

pgxn/neon/Makefile

@@ -5,10 +5,12 @@ MODULE_big = neon
 OBJS = \
 	$(WIN32RES) \
 	communicator.o \
+	communicator_new.o \
 	communicator_process.o \
 	extension_server.o \
 	file_cache.o \
 	hll.o \
+	lfc_prewarm.o \
 	libpagestore.o \
 	logical_replication_monitor.o \
 	neon.o \
@@ -67,6 +69,7 @@ WALPROP_OBJS = \
 
 # libcommunicator.a is built by cargo from the Rust sources under communicator/
 # subdirectory. `cargo build` also generates communicator_bindings.h.
+communicator_new.o: communicator/communicator_bindings.h
 communicator_process.o: communicator/communicator_bindings.h
 file_cache.o: communicator/communicator_bindings.h
 

pgxn/neon/communicator/Cargo.toml

@@ -17,12 +17,30 @@ rest_broker = []
 
 [dependencies]
 axum.workspace = true
+bytes.workspace = true
+clashmap.workspace = true
 http.workspace = true
+libc.workspace = true
+nix.workspace = true
+atomic_enum = "0.3.0"
+measured.workspace = true
+prometheus.workspace = true
+prost.workspace = true
+strum_macros.workspace = true
+thiserror.workspace = true
+tonic = { workspace = true, default-features = false, features=["codegen", "prost", "transport"] }
 tokio = { workspace = true, features = ["macros", "net", "io-util", "rt", "rt-multi-thread"] }
+tokio-pipe = { version = "0.2.12" }
 tracing.workspace = true
 tracing-subscriber.workspace = true
 
-measured.workspace = true
+uring-common = { workspace = true, features = ["bytes"] }
+
+pageserver_client_grpc.workspace = true
+pageserver_api.workspace = true
+pageserver_page_api.workspace = true
+
+neon-shmem.workspace = true
 utils.workspace = true
 workspace_hack = { version = "0.1", path = "../../../workspace_hack" }
 

pgxn/neon/communicator/README.md

@@ -3,9 +3,18 @@
 This package provides the so-called "compute-pageserver communicator",
 or just "communicator" in short. The communicator is a separate
 background worker process that runs in the PostgreSQL server. It's
-part of the neon extension. Currently, it only provides an HTTP
+part of the neon extension.
-endpoint for metrics, but in the future it will evolve to handle all
+
-communications with the pageservers.
+The commuicator handles the communication with the pageservers, and
+also provides an HTTP endpoint for metrics over a local Unix Domain
+socket (aka. the "communicator control socket"). On the PostgreSQL
+side, the glue code in pgxn/neon/ uses the communicator to implement
+the PostgreSQL Storage Manager (SMGR) interface.
+
+## Design criteria
+
+- Low latency
+- Saturate a 10 Gbit / s network interface without becoming a bottleneck
 
 ## Source code view
 
@@ -14,10 +23,122 @@ pgxn/neon/communicator_process.c
     the glue that interacts with PostgreSQL code and the Rust
     code in the communicator process.
 
+pgxn/neon/communicator_new.c
+	Contains the backend code that interacts with the communicator
+	process.
 
-pgxn/neon/communicator/src/worker_process/
+pgxn/neon/communicator/src/backend_interface.rs
-    Worker process main loop and glue code
+	The entry point for calls from each backend.
+
+pgxn/neon/communicator/src/init.rs
+	Initialization at server startup
 
 At compilation time, pgxn/neon/communicator/ produces a static
 library, libcommunicator.a. It is linked to the neon.so extension
 library.
+
+The real networking code, which is independent of PostgreSQL, is in
+the pageserver/client_grpc crate.
+
+## Process view
+
+The communicator runs in a dedicated background worker process, the
+"communicator process". The communicator uses a multi-threaded Tokio
+runtime to execute the IO requests. So the communicator process has
+multiple threads running. That's unusual for Postgres processes and
+care must be taken to make that work.
+
+### Backend <-> worker communication
+
+Each backend has a number of I/O request slots in shared memory. The
+slots are statically allocated for each backend, and must not be
+accessed by other backends. The worker process reads requests from the
+shared memory slots, and writes responses back to the slots.
+
+Here's an example snapshot of the system, when two requests from two
+different backends are in progress:
+
+```
+Backends           Request slots          Communicator process
+---------          -------------          --------------------
+
+Backend 1          1: Idle
+                   2: Idle
+                   3: Processing          tokio task handling request 3
+
+Backend 2          4: Completed
+                   5: Processing          tokio task handling request 5
+                   6: Idle
+
+...                ...
+```
+
+To submit an IO request, the backend first picks one of its Idle
+slots, writes the IO request in the slot, and updates it to
+'Submitted' state. That transfers the ownership of the slot to the
+worker process, until the worker process marks the request as
+Completed. The worker process spawns a separate Tokio task for each
+request.
+
+To inform the worker process that a request slot has a pending IO
+request, there's a pipe shared by the worker process and all backend
+processes. The backend writes the index of the request slot to the
+pipe after changing the slot's state to Submitted. This wakes up the
+worker process.
+
+(Note that the pipe is just used for wakeups, but the worker process
+is free to pick up Submitted IO requests even without receiving the
+wakeup. As of this writing, it doesn't do that, but it might be useful
+in the future to reduce latency even further, for example.)
+
+When the worker process has completed processing the request, it
+writes the result back in the request slot. A GetPage request can also
+contain a pointer to buffer in the shared buffer cache. In that case,
+the worker process writes the resulting page contents directly to the
+buffer, and just a result code in the request slot. It then updates
+the 'state' field to Completed, which passes the owner ship back to
+the originating backend. Finally, it signals the process Latch of the
+originating backend, waking it up.
+
+### Differences between PostgreSQL v16, v17 and v18
+
+PostgreSQL v18 introduced the new AIO mechanism. The PostgreSQL AIO
+mechanism uses a very similar mechanism as described in the previous
+section, for the communication between AIO worker processes and
+backends. With our communicator, the AIO worker processes are not
+used, but we use the same PgAioHandle request slots as in upstream.
+For Neon-specific IO requests like GetDbSize, a neon request slot is
+used. But for the actual IO requests, the request slot merely contains
+a pointer to the PgAioHandle slot. The worker process updates the
+status of that, calls the IO callbacks upon completionetc, just like
+the upstream AIO worker processes do.
+
+## Sequence diagram
+
+                      neon
+    PostgreSQL     extension       backend_interface.rs  worker_process.rs    processor    tonic
+       |               .                    .                   .                 .
+	   | smgr_read()   .                    .                   .                 .
+	   +-------------> +                    .                   .                 .
+	   .               |                    .                   .                 .
+	   .               |  rcommunicator_    .                   .                 .
+	   .               | get_page_at_lsn    .                   .                 .
+	   .               +------------------> +                   .                 .
+                                            |                   .                 .
+                                            | write request to  .                 .                 .
+                                            | slot              .                 .
+                                            |                   .                 .
+                                            |                   .                 .
+											| submit_request()  .                 .
+											+-----------------> +                 .
+											|                   |                 .
+											|					| db_size_request .               .
+																+---------------->.
+																                  . TODO
+
+
+
+### Compute <-> pageserver protocol
+
+The protocol between Compute and the pageserver is based on gRPC. See `protos/`.
+

pgxn/neon/communicator/src/backend_comms.rs

@@ -0,0 +1,224 @@
+//! This module implements a request/response "slot" for submitting
+//! requests from backends to the communicator process.
+//!
+//! NB: The "backend" side of this code runs in Postgres backend processes,
+//! which means that it is not safe to use the 'tracing' crate for logging, nor
+//! to launch threads or use tokio tasks!
+
+use std::cell::UnsafeCell;
+use std::sync::atomic::{AtomicI32, Ordering};
+
+use crate::neon_request::{NeonIORequest, NeonIOResult};
+
+use atomic_enum::atomic_enum;
+
+/// One request/response slot. Each backend has its own set of slots that it
+/// uses.
+///
+/// This is the moral equivalent of PgAioHandle for Postgres AIO requests
+/// Like PgAioHandle, try to keep this small.
+///
+/// There is an array of these in shared memory. Therefore, this must be Sized.
+///
+/// ## Lifecycle of a request
+///
+/// A slot is always owned by either the backend process or the communicator
+/// process, depending on the 'state'. Only the owning process is allowed to
+/// read or modify the slot, except for reading the 'state' itself to check who
+/// owns it.
+///
+/// A slot begins in the Idle state, where it is owned by the backend process.
+/// To submit a request, the backend process fills the slot with the request
+/// data, and changes it to the Submitted state. After changing the state, the
+/// slot is owned by the communicator process, and the backend is not allowed
+/// to access it until the communicator process marks it as Completed.
+///
+/// When the communicator process sees that the slot is in Submitted state, it
+/// starts to process the request. After processing the request, it stores the
+/// result in the slot, and changes the state to Completed. It is now owned by
+/// the backend process again, which may now read the result, and reuse the
+/// slot for a new request.
+///
+/// For correctness of the above protocol, we really only need two states:
+/// "owned by backend" and "owned by communicator process". But to help with
+/// debugging and better assertions, there are a few more states. When the
+/// backend starts to fill in the request details in the slot, it first sets the
+/// state from Idle to Filling, and when it's done with that, from Filling to
+/// Submitted. In the Filling state, the slot is still owned by the
+/// backend. Similarly, when the communicator process starts to process a
+/// request, it sets it to Processing state first, but the slot is still owned
+/// by the communicator process.
+///
+/// This struct doesn't handle waking up the communicator process when a request
+/// has been submitted or when a response is ready. The 'owner_procno' is used
+/// for waking up the backend on completion, but that happens elsewhere.
+pub struct NeonIORequestSlot {
+    /// similar to PgAioHandleState
+    state: AtomicNeonIORequestSlotState,
+
+    /// The owning process's ProcNumber. The worker process uses this to set the
+    /// process's latch on completion.
+    ///
+    /// (This could be calculated from num_neon_request_slots_per_backend and
+    /// the index of this slot in the overall 'neon_requst_slots array'. But we
+    /// prefer the communicator process to not know how the request slots are
+    /// divided between the backends.)
+    owner_procno: AtomicI32,
+
+    /// SAFETY: This is modified by submit_request(), after it has established
+    /// ownership of the slot by setting state from Idle to Filling
+    request: UnsafeCell<NeonIORequest>,
+
+    /// Valid when state is Completed
+    ///
+    /// SAFETY: This is modified by RequestProcessingGuard::complete(). There
+    /// can be only one RequestProcessingGuard outstanding for a slot at a time,
+    /// because it is returned by start_processing_request() which checks the
+    /// state, so RequestProcessingGuard has exclusive access to the slot.
+    result: UnsafeCell<NeonIOResult>,
+}
+
+// The protocol described in the "Lifecycle of a request" section above ensures
+// the safe access to the fields
+unsafe impl Send for NeonIORequestSlot {}
+unsafe impl Sync for NeonIORequestSlot {}
+
+impl Default for NeonIORequestSlot {
+    fn default() -> NeonIORequestSlot {
+        NeonIORequestSlot {
+            owner_procno: AtomicI32::new(-1),
+            request: UnsafeCell::new(NeonIORequest::Empty),
+            result: UnsafeCell::new(NeonIOResult::Empty),
+            state: AtomicNeonIORequestSlotState::new(NeonIORequestSlotState::Idle),
+        }
+    }
+}
+
+#[atomic_enum]
+#[derive(Eq, PartialEq)]
+pub enum NeonIORequestSlotState {
+    Idle,
+
+    /// Backend is filling in the request
+    Filling,
+
+    /// Backend has submitted the request to the communicator, but the
+    /// communicator process has not yet started processing it.
+    Submitted,
+
+    /// Communicator is processing the request
+    Processing,
+
+    /// Communicator has completed the request, and the 'result' field is now
+    /// valid, but the backend has not read the result yet.
+    Completed,
+}
+
+impl NeonIORequestSlot {
+    /// Write a request to the slot, and mark it as Submitted.
+    ///
+    /// Note: This does not wake up the worker process to actually process
+    /// the request. It's the caller's responsibility to do that.
+    pub fn submit_request(&self, request: &NeonIORequest, proc_number: i32) {
+        // Verify that the slot is in Idle state previously, and put it in
+        // Filling state.
+        //
+        // XXX: This step isn't strictly necessary. Assuming the caller didn't
+        // screw up and try to use a slot that's already in use, we could fill
+        // the slot and switch it directly from Idle to Submitted state.
+        if let Err(s) = self.state.compare_exchange(
+            NeonIORequestSlotState::Idle,
+            NeonIORequestSlotState::Filling,
+            Ordering::Relaxed,
+            Ordering::Relaxed,
+        ) {
+            panic!("unexpected state in request slot: {s:?}");
+        }
+
+        // Fill in the request details
+        self.owner_procno.store(proc_number, Ordering::Relaxed);
+        unsafe { *self.request.get() = *request }
+
+        // This synchronizes-with store/swap in [`start_processing_request`].
+        // Note that this ensures that the previous non-atomic writes visible
+        // to other threads too.
+        self.state
+            .store(NeonIORequestSlotState::Submitted, Ordering::Release);
+    }
+
+    pub fn get_state(&self) -> NeonIORequestSlotState {
+        self.state.load(Ordering::Relaxed)
+    }
+
+    pub fn try_get_result(&self) -> Option<NeonIOResult> {
+        // This synchronizes-with the store/swap in [`RequestProcessingGuard::completed`]
+        let state = self.state.load(Ordering::Acquire);
+        if state == NeonIORequestSlotState::Completed {
+            let result = unsafe { *self.result.get() };
+            self.state
+                .store(NeonIORequestSlotState::Idle, Ordering::Relaxed);
+            Some(result)
+        } else {
+            None
+        }
+    }
+
+    /// Read the IO request from the slot indicated in the wakeup
+    pub fn start_processing_request<'a>(&'a self) -> Option<RequestProcessingGuard<'a>> {
+        // XXX: using atomic load rather than compare_exchange would be
+        // sufficient here, as long as the communicator process has _some_ means
+        // of tracking which requests it's already processing. That could be a
+        // flag somewhere in communicator's private memory, for example.
+        //
+        // This synchronizes-with the store in [`submit_request`].
+        if let Err(s) = self.state.compare_exchange(
+            NeonIORequestSlotState::Submitted,
+            NeonIORequestSlotState::Processing,
+            Ordering::Acquire,
+            Ordering::Relaxed,
+        ) {
+            // FIXME surprising state. This is unexpected at the moment, but if we
+            // started to process requests more aggressively, without waiting for the
+            // read from the pipe, then this could happen
+            panic!("unexpected state in request slot: {s:?}");
+        }
+
+        Some(RequestProcessingGuard(self))
+    }
+}
+
+/// [`NeonIORequestSlot::start_processing_request`] returns this guard object to
+/// indicate that the the caller now "owns" the slot, until it calls
+/// [`RequestProcessingGuard::completed`].
+///
+/// TODO: implement Drop on this, to mark the request as Aborted or Errored
+/// if [`RequestProcessingGuard::completed`] is not called.
+pub struct RequestProcessingGuard<'a>(&'a NeonIORequestSlot);
+
+unsafe impl<'a> Send for RequestProcessingGuard<'a> {}
+unsafe impl<'a> Sync for RequestProcessingGuard<'a> {}
+
+impl<'a> RequestProcessingGuard<'a> {
+    pub fn get_request(&self) -> &NeonIORequest {
+        unsafe { &*self.0.request.get() }
+    }
+
+    pub fn get_owner_procno(&self) -> i32 {
+        self.0.owner_procno.load(Ordering::Relaxed)
+    }
+
+    pub fn completed(self, result: NeonIOResult) {
+        // Store the result to the slot.
+        unsafe {
+            *self.0.result.get() = result;
+        };
+
+        // Mark the request as completed. After that, we no longer have
+        // ownership of the slot, and must not modify it.
+        let old_state = self
+            .0
+            .state
+            .swap(NeonIORequestSlotState::Completed, Ordering::Release);
+        assert!(old_state == NeonIORequestSlotState::Processing);
+    }
+}

pgxn/neon/communicator/src/backend_interface.rs

@@ -0,0 +1,296 @@
+//! This code runs in each backend process. That means that launching Rust threads, panicking
+//! etc. is forbidden!
+
+use std::os::fd::OwnedFd;
+
+use crate::backend_comms::NeonIORequestSlot;
+use crate::init::CommunicatorInitStruct;
+use crate::integrated_cache::{BackendCacheReadOp, IntegratedCacheReadAccess};
+use crate::neon_request::{CCachedGetPageVResult, CLsn, COid};
+use crate::neon_request::{NeonIORequest, NeonIOResult};
+
+use utils::lsn::Lsn;
+
+pub struct CommunicatorBackendStruct<'t> {
+    my_proc_number: i32,
+
+    neon_request_slots: &'t [NeonIORequestSlot],
+
+    submission_pipe_write_fd: OwnedFd,
+
+    pending_cache_read_op: Option<BackendCacheReadOp<'t>>,
+
+    integrated_cache: &'t IntegratedCacheReadAccess<'t>,
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn rcommunicator_backend_init(
+    cis: Box<CommunicatorInitStruct>,
+    my_proc_number: i32,
+) -> &'static mut CommunicatorBackendStruct<'static> {
+    if my_proc_number < 0 {
+        panic!("cannot attach to communicator shared memory with procnumber {my_proc_number}");
+    }
+
+    let integrated_cache = Box::leak(Box::new(cis.integrated_cache_init_struct.backend_init()));
+
+    let bs: &'static mut CommunicatorBackendStruct =
+        Box::leak(Box::new(CommunicatorBackendStruct {
+            my_proc_number,
+            neon_request_slots: cis.neon_request_slots,
+
+            submission_pipe_write_fd: cis.submission_pipe_write_fd,
+            pending_cache_read_op: None,
+
+            integrated_cache,
+        }));
+    bs
+}
+
+/// Start a request. You can poll for its completion and get the result by
+/// calling bcomm_poll_dbsize_request_completion(). The communicator will wake
+/// us up by setting our process latch, so to wait for the completion, wait on
+/// the latch and call bcomm_poll_dbsize_request_completion() every time the
+/// latch is set.
+///
+/// Safety: The C caller must ensure that the references are valid.
+/// The requested slot must be free, or this panics.
+#[unsafe(no_mangle)]
+pub extern "C" fn bcomm_start_io_request(
+    bs: &'_ mut CommunicatorBackendStruct,
+    slot_idx: i32,
+    request: &NeonIORequest,
+    immediate_result_ptr: &mut NeonIOResult,
+) -> i32 {
+    assert!(bs.pending_cache_read_op.is_none());
+
+    // Check if the request can be satisfied from the cache first
+    if let NeonIORequest::RelSize(req) = request {
+        if let Some(nblocks) = bs.integrated_cache.get_rel_size(&req.reltag()) {
+            *immediate_result_ptr = NeonIOResult::RelSize(nblocks);
+            return -1;
+        }
+    }
+
+    // Create neon request and submit it
+    bs.start_neon_io_request(slot_idx, request);
+
+    slot_idx
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn bcomm_start_get_page_v_request(
+    bs: &mut CommunicatorBackendStruct,
+    slot_idx: i32,
+    request: &NeonIORequest,
+    immediate_result_ptr: &mut CCachedGetPageVResult,
+) -> i32 {
+    let NeonIORequest::GetPageV(get_pagev_request) = request else {
+        panic!("invalid request passed to bcomm_start_get_page_v_request()");
+    };
+    assert!(matches!(request, NeonIORequest::GetPageV(_)));
+    assert!(bs.pending_cache_read_op.is_none());
+
+    // Check if the request can be satisfied from the cache first
+    let mut all_cached = true;
+    let mut read_op = bs.integrated_cache.start_read_op();
+    for i in 0..get_pagev_request.nblocks {
+        if let Some(cache_block) = read_op.get_page(
+            &get_pagev_request.reltag(),
+            get_pagev_request.block_number + i as u32,
+        ) {
+            immediate_result_ptr.cache_block_numbers[i as usize] = cache_block;
+        } else {
+            // not found in cache
+            all_cached = false;
+            break;
+        }
+    }
+    if all_cached {
+        bs.pending_cache_read_op = Some(read_op);
+        return -1;
+    }
+
+    // Create neon request and submit it
+    bs.start_neon_io_request(slot_idx, request);
+
+    slot_idx
+}
+
+/// Check if a request has completed. Returns:
+///
+/// -1 if the request is still being processed
+/// 0 on success
+#[unsafe(no_mangle)]
+pub extern "C" fn bcomm_poll_request_completion(
+    bs: &mut CommunicatorBackendStruct,
+    request_slot_idx: u32,
+    result_p: &mut NeonIOResult,
+) -> i32 {
+    match bs.neon_request_slots[request_slot_idx as usize].try_get_result() {
+        None => -1, // still processing
+        Some(result) => {
+            *result_p = result;
+            0
+        }
+    }
+}
+
+/// Check if a request has completed. Returns:
+///
+/// 'false' if the slot is Idle. The backend process has ownership.
+/// 'true' if the slot is busy, and should be polled for result.
+#[unsafe(no_mangle)]
+pub extern "C" fn bcomm_get_request_slot_status(
+    bs: &mut CommunicatorBackendStruct,
+    request_slot_idx: u32,
+) -> bool {
+    use crate::backend_comms::NeonIORequestSlotState;
+    match bs.neon_request_slots[request_slot_idx as usize].get_state() {
+        NeonIORequestSlotState::Idle => false,
+        NeonIORequestSlotState::Filling => {
+            // 'false' would be the right result here. However, this
+            // is a very transient state. The C code should never
+            // leave a slot in this state, so if it sees that,
+            // something's gone wrong and it's not clear what to do
+            // with it.
+            panic!("unexpected Filling state in request slot {request_slot_idx}");
+        }
+        NeonIORequestSlotState::Submitted => true,
+        NeonIORequestSlotState::Processing => true,
+        NeonIORequestSlotState::Completed => true,
+    }
+}
+
+// LFC functions
+
+/// Finish a local file cache read
+///
+//
+#[unsafe(no_mangle)]
+pub extern "C" fn bcomm_finish_cache_read(bs: &mut CommunicatorBackendStruct) -> bool {
+    if let Some(op) = bs.pending_cache_read_op.take() {
+        op.finish()
+    } else {
+        panic!("bcomm_finish_cache_read() called with no cached read pending");
+    }
+}
+
+/// Check if LFC contains the given buffer, and update its last-written LSN if not.
+///
+/// This is used in WAL replay in read replica, to skip updating pages that are
+/// not in cache.
+#[unsafe(no_mangle)]
+pub extern "C" fn bcomm_update_lw_lsn_for_block_if_not_cached(
+    bs: &mut CommunicatorBackendStruct,
+    spc_oid: COid,
+    db_oid: COid,
+    rel_number: u32,
+    fork_number: u8,
+    block_number: u32,
+    lsn: CLsn,
+) -> bool {
+    bs.integrated_cache.update_lw_lsn_for_block_if_not_cached(
+        &pageserver_page_api::RelTag {
+            spcnode: spc_oid,
+            dbnode: db_oid,
+            relnode: rel_number,
+            forknum: fork_number,
+        },
+        block_number,
+        Lsn(lsn),
+    )
+}
+
+#[repr(C)]
+#[derive(Clone, Debug)]
+pub struct FileCacheIterator {
+    next_bucket: u64,
+
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+}
+
+/// Iterate over LFC contents
+#[allow(clippy::missing_safety_doc)]
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn bcomm_cache_iterate_begin(
+    _bs: &mut CommunicatorBackendStruct,
+    iter: *mut FileCacheIterator,
+) {
+    unsafe { (*iter).next_bucket = 0 };
+}
+
+#[allow(clippy::missing_safety_doc)]
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn bcomm_cache_iterate_next(
+    bs: &mut CommunicatorBackendStruct,
+    iter: *mut FileCacheIterator,
+) -> bool {
+    use crate::integrated_cache::GetBucketResult;
+    loop {
+        let next_bucket = unsafe { (*iter).next_bucket } as usize;
+        match bs.integrated_cache.get_bucket(next_bucket) {
+            GetBucketResult::Occupied(rel, blk) => {
+                unsafe {
+                    (*iter).spc_oid = rel.spcnode;
+                    (*iter).db_oid = rel.dbnode;
+                    (*iter).rel_number = rel.relnode;
+                    (*iter).fork_number = rel.forknum;
+                    (*iter).block_number = blk;
+
+                    (*iter).next_bucket += 1;
+                }
+                break true;
+            }
+            GetBucketResult::Vacant => {
+                unsafe {
+                    (*iter).next_bucket += 1;
+                }
+                continue;
+            }
+            GetBucketResult::OutOfBounds => {
+                break false;
+            }
+        }
+    }
+}
+
+#[allow(clippy::missing_safety_doc)]
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn bcomm_cache_get_num_pages_used(bs: &mut CommunicatorBackendStruct) -> u64 {
+    bs.integrated_cache.get_num_buckets_in_use() as u64
+}
+
+impl<'t> CommunicatorBackendStruct<'t> {
+    /// The slot must be free, or this panics.
+    pub(crate) fn start_neon_io_request(&mut self, request_slot_idx: i32, request: &NeonIORequest) {
+        let my_proc_number = self.my_proc_number;
+
+        self.neon_request_slots[request_slot_idx as usize].submit_request(request, my_proc_number);
+
+        // Tell the communicator about it
+        self.notify_about_request(request_slot_idx);
+    }
+
+    /// Send a wakeup to the communicator process
+    fn notify_about_request(self: &CommunicatorBackendStruct<'t>, request_slot_idx: i32) {
+        // wake up communicator by writing the idx to the submission pipe
+        //
+
+        // This can block, if the pipe is full. That should be very rare,
+        // because the communicator tries hard to drain the pipe to prevent
+        // that. Also, there's a natural upper bound on how many wakeups can be
+        // queued up: there is only a limited number of request slots for each
+        // backend.
+        //
+        // If it does block very briefly, that's not too serious.
+        let idxbuf = request_slot_idx.to_ne_bytes();
+
+        let _res = nix::unistd::write(&self.submission_pipe_write_fd, &idxbuf);
+        // FIXME: check result, return any errors
+    }
+}

pgxn/neon/communicator/src/file_cache.rs

@@ -0,0 +1,156 @@
+//! Implement the "low-level" parts of the file cache.
+//!
+//! This module just deals with reading and writing the file, and keeping track
+//! which blocks in the cache file are in use and which are free. The "high
+//! level" parts of tracking which block in the cache file corresponds to which
+//! relation block is handled in 'integrated_cache' instead.
+//!
+//! This module is only used to access the file from the communicator
+//! process. The backend processes *also* read the file (and sometimes also
+//! write it? ), but the backends use direct C library calls for that.
+use std::fs::File;
+use std::os::unix::fs::FileExt;
+use std::path::Path;
+use std::sync::Arc;
+use std::sync::Mutex;
+
+use measured::metric;
+use measured::metric::MetricEncoding;
+use measured::metric::gauge::GaugeState;
+use measured::{Gauge, MetricGroup};
+
+use crate::BLCKSZ;
+
+use tokio::task::spawn_blocking;
+
+pub type CacheBlock = u64;
+
+pub const INVALID_CACHE_BLOCK: CacheBlock = u64::MAX;
+
+pub struct FileCache {
+    file: Arc<File>,
+
+    free_list: Mutex<FreeList>,
+
+    metrics: FileCacheMetricGroup,
+}
+
+#[derive(MetricGroup)]
+#[metric(new())]
+struct FileCacheMetricGroup {
+    /// Local File Cache size in 8KiB blocks
+    max_blocks: Gauge,
+
+    /// Number of free 8KiB blocks in Local File Cache
+    num_free_blocks: Gauge,
+}
+
+// TODO: We keep track of all free blocks in this vec. That doesn't really scale.
+// Idea: when free_blocks fills up with more than 1024 entries, write them all to
+// one block on disk.
+#[derive(Debug)]
+struct FreeList {
+    next_free_block: CacheBlock,
+    max_blocks: u64,
+
+    free_blocks: Vec<CacheBlock>,
+}
+
+impl FileCache {
+    pub fn new(file_cache_path: &Path, mut initial_size: u64) -> Result<FileCache, std::io::Error> {
+        if initial_size < 100 {
+            tracing::warn!(
+                "min size for file cache is 100 blocks, {} requested",
+                initial_size
+            );
+            initial_size = 100;
+        }
+
+        let file = std::fs::OpenOptions::new()
+            .read(true)
+            .write(true)
+            .truncate(true)
+            .create(true)
+            .open(file_cache_path)?;
+
+        tracing::info!("initialized file cache with {} blocks", initial_size);
+
+        Ok(FileCache {
+            file: Arc::new(file),
+            free_list: Mutex::new(FreeList {
+                next_free_block: 0,
+                max_blocks: initial_size,
+                free_blocks: Vec::new(),
+            }),
+            metrics: FileCacheMetricGroup::new(),
+        })
+    }
+
+    // File cache management
+
+    pub async fn read_block(
+        &self,
+        cache_block: CacheBlock,
+        mut dst: impl uring_common::buf::IoBufMut + Send + Sync,
+    ) -> Result<(), std::io::Error> {
+        assert!(dst.bytes_total() == BLCKSZ);
+        let file = self.file.clone();
+
+        let dst_ref = unsafe { std::slice::from_raw_parts_mut(dst.stable_mut_ptr(), BLCKSZ) };
+
+        spawn_blocking(move || file.read_exact_at(dst_ref, cache_block * BLCKSZ as u64)).await??;
+        Ok(())
+    }
+
+    pub async fn write_block(
+        &self,
+        cache_block: CacheBlock,
+        src: impl uring_common::buf::IoBuf + Send + Sync,
+    ) -> Result<(), std::io::Error> {
+        assert!(src.bytes_init() == BLCKSZ);
+        let file = self.file.clone();
+
+        let src_ref = unsafe { std::slice::from_raw_parts(src.stable_ptr(), BLCKSZ) };
+
+        spawn_blocking(move || file.write_all_at(src_ref, cache_block * BLCKSZ as u64)).await??;
+
+        Ok(())
+    }
+
+    pub fn alloc_block(&self) -> Option<CacheBlock> {
+        let mut free_list = self.free_list.lock().unwrap();
+        if let Some(x) = free_list.free_blocks.pop() {
+            return Some(x);
+        }
+        if free_list.next_free_block < free_list.max_blocks {
+            let result = free_list.next_free_block;
+            free_list.next_free_block += 1;
+            return Some(result);
+        }
+        None
+    }
+
+    pub fn dealloc_block(&self, cache_block: CacheBlock) {
+        let mut free_list = self.free_list.lock().unwrap();
+        free_list.free_blocks.push(cache_block);
+    }
+}
+
+impl<T: metric::group::Encoding> MetricGroup<T> for FileCache
+where
+    GaugeState: MetricEncoding<T>,
+{
+    fn collect_group_into(&self, enc: &mut T) -> Result<(), <T as metric::group::Encoding>::Err> {
+        // Update the gauges with fresh values first
+        {
+            let free_list = self.free_list.lock().unwrap();
+            self.metrics.max_blocks.set(free_list.max_blocks as i64);
+
+            let total_free_blocks: i64 = free_list.free_blocks.len() as i64
+                + (free_list.max_blocks as i64 - free_list.next_free_block as i64);
+            self.metrics.num_free_blocks.set(total_free_blocks);
+        }
+
+        self.metrics.collect_group_into(enc)
+    }
+}

pgxn/neon/communicator/src/global_allocator.rs

@@ -0,0 +1,107 @@
+//! Global allocator, for tracking memory usage of the Rust parts
+//!
+//! Postgres is designed to handle allocation failure (ie. malloc() returning NULL) gracefully.  It
+//! rolls backs the transaction and gives the user an "ERROR: out of memory" error. Rust code
+//! however panics if an allocation fails. We don't want that to ever happen, because an unhandled
+//! panic leads to Postgres crash and restart. Our strategy is to pre-allocate a large enough chunk
+//! of memory for use by the Rust code, so that the allocations never fail.
+//!
+//! To pick the size for the pre-allocated chunk, we have a metric to track the high watermark
+//! memory usage of all the Rust allocations in total.
+//!
+//! TODO:
+//!
+//! - Currently we just export the metrics. Actual allocations are still just passed through to
+//!   the system allocator.
+//! - Take padding etc. overhead into account
+
+use std::alloc::{GlobalAlloc, Layout, System};
+use std::sync::atomic::{AtomicU64, AtomicUsize, Ordering};
+
+use measured::metric;
+use measured::metric::MetricEncoding;
+use measured::metric::gauge::GaugeState;
+use measured::{Gauge, MetricGroup};
+
+pub(crate) struct MyAllocator {
+    allocations: AtomicU64,
+    deallocations: AtomicU64,
+
+    allocated: AtomicUsize,
+    high: AtomicUsize,
+}
+
+#[derive(MetricGroup)]
+#[metric(new())]
+struct MyAllocatorMetricGroup {
+    /// Number of allocations in Rust code
+    communicator_mem_allocations: Gauge,
+
+    /// Number of deallocations in Rust code
+    communicator_mem_deallocations: Gauge,
+
+    /// Bytes currently allocated
+    communicator_mem_allocated: Gauge,
+
+    /// High watermark of allocated bytes
+    communicator_mem_high: Gauge,
+}
+
+unsafe impl GlobalAlloc for MyAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        self.allocations.fetch_add(1, Ordering::Relaxed);
+        let mut allocated = self.allocated.fetch_add(layout.size(), Ordering::Relaxed);
+        allocated += layout.size();
+        self.high.fetch_max(allocated, Ordering::Relaxed);
+        unsafe { System.alloc(layout) }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        self.deallocations.fetch_add(1, Ordering::Relaxed);
+        self.allocated.fetch_sub(layout.size(), Ordering::Relaxed);
+        unsafe { System.dealloc(ptr, layout) }
+    }
+}
+
+#[global_allocator]
+static GLOBAL: MyAllocator = MyAllocator {
+    allocations: AtomicU64::new(0),
+    deallocations: AtomicU64::new(0),
+    allocated: AtomicUsize::new(0),
+    high: AtomicUsize::new(0),
+};
+
+pub(crate) struct MyAllocatorCollector {
+    metrics: MyAllocatorMetricGroup,
+}
+
+impl MyAllocatorCollector {
+    pub(crate) fn new() -> Self {
+        Self {
+            metrics: MyAllocatorMetricGroup::new(),
+        }
+    }
+}
+
+impl<T: metric::group::Encoding> MetricGroup<T> for MyAllocatorCollector
+where
+    GaugeState: MetricEncoding<T>,
+{
+    fn collect_group_into(&self, enc: &mut T) -> Result<(), <T as metric::group::Encoding>::Err> {
+        // Update the gauges with fresh values first
+        self.metrics
+            .communicator_mem_allocations
+            .set(GLOBAL.allocations.load(Ordering::Relaxed) as i64);
+        self.metrics
+            .communicator_mem_deallocations
+            .set(GLOBAL.allocations.load(Ordering::Relaxed) as i64);
+        self.metrics
+            .communicator_mem_allocated
+            .set(GLOBAL.allocated.load(Ordering::Relaxed) as i64);
+        self.metrics
+            .communicator_mem_high
+            .set(GLOBAL.high.load(Ordering::Relaxed) as i64);
+
+        self.metrics.collect_group_into(enc)
+    }
+}

pgxn/neon/communicator/src/init.rs

@@ -0,0 +1,166 @@
+//! Initialization functions. These are executed in the postmaster process,
+//! at different stages of server startup.
+//!
+//!
+//! Communicator initialization steps:
+//!
+//! 1. At postmaster startup, before shared memory is allocated,
+//!    rcommunicator_shmem_size() is called to get the amount of
+//!    shared memory that this module needs.
+//!
+//! 2. Later, after the shared memory has been allocated,
+//!    rcommunicator_shmem_init() is called to initialize the shmem
+//!    area.
+//!
+//! Per process initialization:
+//!
+//! When a backend process starts up, it calls rcommunicator_backend_init().
+//! In the communicator worker process, other functions are called, see
+//! `worker_process` module.
+
+use std::ffi::c_int;
+use std::mem;
+use std::mem::MaybeUninit;
+use std::os::fd::OwnedFd;
+
+use crate::backend_comms::NeonIORequestSlot;
+use crate::integrated_cache::IntegratedCacheInitStruct;
+
+/// This struct is created in the postmaster process, and inherited to
+/// the communicator process and all backend processes through fork()
+#[repr(C)]
+pub struct CommunicatorInitStruct {
+    pub submission_pipe_read_fd: OwnedFd,
+    pub submission_pipe_write_fd: OwnedFd,
+
+    // Shared memory data structures
+    pub num_neon_request_slots: u32,
+
+    pub neon_request_slots: &'static [NeonIORequestSlot],
+
+    pub integrated_cache_init_struct: IntegratedCacheInitStruct<'static>,
+}
+
+impl std::fmt::Debug for CommunicatorInitStruct {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        fmt.debug_struct("CommunicatorInitStruct")
+            .field("submission_pipe_read_fd", &self.submission_pipe_read_fd)
+            .field("submission_pipe_write_fd", &self.submission_pipe_write_fd)
+            .field("num_neon_request_slots", &self.num_neon_request_slots)
+            .field("neon_request_slots length", &self.neon_request_slots.len())
+            .finish()
+    }
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn rcommunicator_shmem_size(num_neon_request_slots: u32) -> u64 {
+    let mut size = 0;
+
+    size += mem::size_of::<NeonIORequestSlot>() * num_neon_request_slots as usize;
+
+    // For integrated_cache's Allocator. TODO: make this adjustable
+    size += IntegratedCacheInitStruct::shmem_size();
+
+    size as u64
+}
+
+/// Initialize the shared memory segment. Returns a backend-private
+/// struct, which will be inherited by backend processes through fork
+#[unsafe(no_mangle)]
+pub extern "C" fn rcommunicator_shmem_init(
+    submission_pipe_read_fd: c_int,
+    submission_pipe_write_fd: c_int,
+    num_neon_request_slots: u32,
+    shmem_area_ptr: *mut MaybeUninit<u8>,
+    shmem_area_len: u64,
+    initial_file_cache_size: u64,
+    max_file_cache_size: u64,
+) -> &'static mut CommunicatorInitStruct {
+    let shmem_area: &'static mut [MaybeUninit<u8>] =
+        unsafe { std::slice::from_raw_parts_mut(shmem_area_ptr, shmem_area_len as usize) };
+
+    let (neon_request_slots, remaining_area) =
+        alloc_array_from_slice::<NeonIORequestSlot>(shmem_area, num_neon_request_slots as usize);
+
+    for slot in neon_request_slots.iter_mut() {
+        slot.write(NeonIORequestSlot::default());
+    }
+
+    // 'neon_request_slots' is initialized now. (MaybeUninit::slice_assume_init_mut() is nightly-only
+    // as of this writing.)
+    let neon_request_slots = unsafe {
+        std::mem::transmute::<&mut [MaybeUninit<NeonIORequestSlot>], &mut [NeonIORequestSlot]>(
+            neon_request_slots,
+        )
+    };
+
+    // Give the rest of the area to the integrated cache
+    let integrated_cache_init_struct = IntegratedCacheInitStruct::shmem_init(
+        remaining_area,
+        initial_file_cache_size,
+        max_file_cache_size,
+    );
+
+    let (submission_pipe_read_fd, submission_pipe_write_fd) = unsafe {
+        use std::os::fd::FromRawFd;
+        (
+            OwnedFd::from_raw_fd(submission_pipe_read_fd),
+            OwnedFd::from_raw_fd(submission_pipe_write_fd),
+        )
+    };
+
+    let cis: &'static mut CommunicatorInitStruct = Box::leak(Box::new(CommunicatorInitStruct {
+        submission_pipe_read_fd,
+        submission_pipe_write_fd,
+
+        num_neon_request_slots,
+        neon_request_slots,
+
+        integrated_cache_init_struct,
+    }));
+
+    cis
+}
+
+pub fn alloc_from_slice<T>(
+    area: &mut [MaybeUninit<u8>],
+) -> (&mut MaybeUninit<T>, &mut [MaybeUninit<u8>]) {
+    let layout = std::alloc::Layout::new::<T>();
+
+    let area_start = area.as_mut_ptr();
+
+    // pad to satisfy alignment requirements
+    let padding = area_start.align_offset(layout.align());
+    if padding + layout.size() > area.len() {
+        panic!("out of memory");
+    }
+    let area = &mut area[padding..];
+    let (result_area, remain) = area.split_at_mut(layout.size());
+
+    let result_ptr: *mut MaybeUninit<T> = result_area.as_mut_ptr().cast();
+    let result = unsafe { result_ptr.as_mut().unwrap() };
+
+    (result, remain)
+}
+
+pub fn alloc_array_from_slice<T>(
+    area: &mut [MaybeUninit<u8>],
+    len: usize,
+) -> (&mut [MaybeUninit<T>], &mut [MaybeUninit<u8>]) {
+    let layout = std::alloc::Layout::new::<T>();
+
+    let area_start = area.as_mut_ptr();
+
+    // pad to satisfy alignment requirements
+    let padding = area_start.align_offset(layout.align());
+    if padding + layout.size() * len > area.len() {
+        panic!("out of memory");
+    }
+    let area = &mut area[padding..];
+    let (result_area, remain) = area.split_at_mut(layout.size() * len);
+
+    let result_ptr: *mut MaybeUninit<T> = result_area.as_mut_ptr().cast();
+    let result = unsafe { std::slice::from_raw_parts_mut(result_ptr.as_mut().unwrap(), len) };
+
+    (result, remain)
+}

pgxn/neon/communicator/src/integrated_cache.rs

@@ -0,0 +1,990 @@
+//! Integrated communicator cache
+//!
+//! It tracks:
+//! - Relation sizes and existence
+//! - Last-written LSN
+//! - Block cache (also known as LFC)
+//!
+//! TODO: limit the size
+//! TODO: concurrency
+//!
+//! Note: This deals with "relations" which is really just one "relation fork" in Postgres
+//! terms. RelFileLocator + ForkNumber is the key.
+
+//
+// TODO: Thoughts on eviction:
+//
+// There are two things we need to track, and evict if we run out of space:
+// - blocks in the file cache's file. If the file grows too large, need to evict something.
+//   Also if the cache is resized
+//
+// - entries in the cache map. If we run out of memory in the shmem area, need to evict
+//   something
+//
+
+use std::mem::MaybeUninit;
+use std::sync::atomic::{AtomicBool, AtomicU32, AtomicU64, AtomicUsize, Ordering};
+
+use utils::lsn::{AtomicLsn, Lsn};
+
+use crate::file_cache::INVALID_CACHE_BLOCK;
+use crate::file_cache::{CacheBlock, FileCache};
+use crate::init::alloc_from_slice;
+use pageserver_page_api::RelTag;
+
+use measured::metric;
+use measured::metric::MetricEncoding;
+use measured::metric::counter::CounterState;
+use measured::metric::gauge::GaugeState;
+use measured::{Counter, Gauge, MetricGroup};
+
+use neon_shmem::hash::{HashMapInit, entry::Entry};
+use neon_shmem::shmem::ShmemHandle;
+
+// in # of entries
+const RELSIZE_CACHE_SIZE: u32 = 64 * 1024;
+
+/// This struct is initialized at postmaster startup, and passed to all the processes via fork().
+pub struct IntegratedCacheInitStruct<'t> {
+    shared: &'t IntegratedCacheShared,
+    relsize_cache_handle: HashMapInit<'t, RelKey, RelEntry>,
+    block_map_handle: HashMapInit<'t, BlockKey, BlockEntry>,
+}
+
+/// This struct is allocated in the (fixed-size) shared memory area at postmaster startup.
+/// It is accessible by all the backends and the communicator process.
+#[derive(Debug)]
+pub struct IntegratedCacheShared {
+    global_lw_lsn: AtomicU64,
+}
+
+/// Represents write-access to the integrated cache. This is used by the communicator process.
+pub struct IntegratedCacheWriteAccess<'t> {
+    shared: &'t IntegratedCacheShared,
+    relsize_cache: neon_shmem::hash::HashMapAccess<'t, RelKey, RelEntry>,
+    block_map: neon_shmem::hash::HashMapAccess<'t, BlockKey, BlockEntry>,
+
+    pub(crate) file_cache: Option<FileCache>,
+
+    // Fields for eviction
+    clock_hand: AtomicUsize,
+
+    metrics: IntegratedCacheMetricGroup,
+}
+
+#[derive(MetricGroup)]
+#[metric(new())]
+struct IntegratedCacheMetricGroup {
+    /// Page evictions from the Local File Cache
+    cache_page_evictions_counter: Counter,
+
+    /// Block entry evictions from the integrated cache
+    block_entry_evictions_counter: Counter,
+
+    /// Number of times the clock hand has moved
+    clock_iterations_counter: Counter,
+
+    // metrics from the hash map
+    /// Allocated size of the block cache hash map
+    block_map_num_buckets: Gauge,
+
+    /// Number of buckets in use in the block cache hash map
+    block_map_num_buckets_in_use: Gauge,
+
+    /// Allocated size of the relsize cache hash map
+    relsize_cache_num_buckets: Gauge,
+
+    /// Number of buckets in use in the relsize cache hash map
+    relsize_cache_num_buckets_in_use: Gauge,
+}
+
+/// Represents read-only access to the integrated cache. Backend processes have this.
+pub struct IntegratedCacheReadAccess<'t> {
+    shared: &'t IntegratedCacheShared,
+    relsize_cache: neon_shmem::hash::HashMapAccess<'t, RelKey, RelEntry>,
+    block_map: neon_shmem::hash::HashMapAccess<'t, BlockKey, BlockEntry>,
+}
+
+impl<'t> IntegratedCacheInitStruct<'t> {
+    /// Return the desired size in bytes of the fixed-size shared memory area to reserve for the
+    /// integrated cache.
+    pub fn shmem_size() -> usize {
+        // The relsize cache is fixed-size. The block map is allocated in a separate resizable
+        // area.
+        let mut sz = 0;
+        sz += std::mem::size_of::<IntegratedCacheShared>();
+        sz += HashMapInit::<RelKey, RelEntry>::estimate_size(RELSIZE_CACHE_SIZE);
+
+        sz
+    }
+
+    /// Initialize the shared memory segment. This runs once in postmaster. Returns a struct which
+    /// will be inherited by all processes through fork.
+    pub fn shmem_init(
+        shmem_area: &'t mut [MaybeUninit<u8>],
+        initial_file_cache_size: u64,
+        max_file_cache_size: u64,
+    ) -> IntegratedCacheInitStruct<'t> {
+        // Initialize the shared struct
+        let (shared, remain_shmem_area) = alloc_from_slice::<IntegratedCacheShared>(shmem_area);
+        let shared = shared.write(IntegratedCacheShared {
+            global_lw_lsn: AtomicU64::new(0),
+        });
+
+        // Use the remaining part of the fixed-size area for the relsize cache
+        let relsize_cache_handle =
+            neon_shmem::hash::HashMapInit::with_fixed(RELSIZE_CACHE_SIZE, remain_shmem_area);
+
+        let max_bytes =
+            HashMapInit::<BlockKey, BlockEntry>::estimate_size(max_file_cache_size as u32);
+
+        // Initialize the block map in a separate resizable shared memory area
+        let shmem_handle = ShmemHandle::new("block mapping", 0, max_bytes).unwrap();
+
+        let block_map_handle =
+            neon_shmem::hash::HashMapInit::with_shmem(initial_file_cache_size as u32, shmem_handle);
+        IntegratedCacheInitStruct {
+            shared,
+            relsize_cache_handle,
+            block_map_handle,
+        }
+    }
+
+    /// Initialize access to the integrated cache for the communicator worker process
+    pub fn worker_process_init(
+        self,
+        lsn: Lsn,
+        file_cache: Option<FileCache>,
+    ) -> IntegratedCacheWriteAccess<'t> {
+        let IntegratedCacheInitStruct {
+            shared,
+            relsize_cache_handle,
+            block_map_handle,
+        } = self;
+
+        shared.global_lw_lsn.store(lsn.0, Ordering::Relaxed);
+
+        IntegratedCacheWriteAccess {
+            shared,
+            relsize_cache: relsize_cache_handle.attach_writer(),
+            block_map: block_map_handle.attach_writer(),
+            file_cache,
+            clock_hand: AtomicUsize::new(0),
+            metrics: IntegratedCacheMetricGroup::new(),
+        }
+    }
+
+    /// Initialize access to the integrated cache for a backend process
+    pub fn backend_init(self) -> IntegratedCacheReadAccess<'t> {
+        let IntegratedCacheInitStruct {
+            shared,
+            relsize_cache_handle,
+            block_map_handle,
+        } = self;
+
+        IntegratedCacheReadAccess {
+            shared,
+            relsize_cache: relsize_cache_handle.attach_reader(),
+            block_map: block_map_handle.attach_reader(),
+        }
+    }
+}
+
+/// Value stored in the cache mapping hash table.
+struct BlockEntry {
+    lw_lsn: AtomicLsn,
+    cache_block: AtomicU64,
+
+    pinned: AtomicU64,
+
+    // 'referenced' bit for the clock algorithm
+    referenced: AtomicBool,
+}
+
+/// Value stored in the relsize cache hash table.
+struct RelEntry {
+    /// cached size of the relation
+    /// u32::MAX means 'not known' (that's InvalidBlockNumber in Postgres)
+    nblocks: AtomicU32,
+
+    /// This is the last time the "metadata" of this relation changed, not
+    /// the contents of the blocks. That is, the size of the relation.
+    lw_lsn: AtomicLsn,
+}
+
+impl std::fmt::Debug for RelEntry {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        fmt.debug_struct("Rel")
+            .field("nblocks", &self.nblocks.load(Ordering::Relaxed))
+            .finish()
+    }
+}
+impl std::fmt::Debug for BlockEntry {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        fmt.debug_struct("Block")
+            .field("lw_lsn", &self.lw_lsn.load())
+            .field("cache_block", &self.cache_block.load(Ordering::Relaxed))
+            .field("pinned", &self.pinned.load(Ordering::Relaxed))
+            .field("referenced", &self.referenced.load(Ordering::Relaxed))
+            .finish()
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, PartialOrd, Eq, Hash, Ord)]
+struct RelKey(RelTag);
+
+impl From<&RelTag> for RelKey {
+    fn from(val: &RelTag) -> RelKey {
+        RelKey(*val)
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, PartialOrd, Eq, Hash, Ord)]
+struct BlockKey {
+    rel: RelTag,
+    block_number: u32,
+}
+
+impl From<(&RelTag, u32)> for BlockKey {
+    fn from(val: (&RelTag, u32)) -> BlockKey {
+        BlockKey {
+            rel: *val.0,
+            block_number: val.1,
+        }
+    }
+}
+
+/// Return type used in the cache's get_*() functions. 'Found' means that the page, or other
+/// information that was enqueried, exists in the cache. '
+pub enum CacheResult<V> {
+    /// The enqueried page or other information existed in the cache.
+    Found(V),
+
+    /// The cache doesn't contain the page (or other enqueried information, like relation size). The
+    /// Lsn is the 'not_modified_since' LSN that should be used in the request to the pageserver to
+    /// read the page.
+    NotFound(Lsn),
+}
+
+/// Return type of [try_evict_entry]
+enum EvictResult {
+    /// Could not evict page because it was pinned
+    Pinned,
+
+    /// The victim bucket was already vacant
+    Vacant,
+
+    /// Evicted an entry. If it had a cache block associated with it, it's returned
+    /// here, otherwise None
+    Evicted(Option<CacheBlock>),
+}
+
+impl<'t> IntegratedCacheWriteAccess<'t> {
+    pub fn get_rel_size(&'t self, rel: &RelTag) -> CacheResult<u32> {
+        if let Some(nblocks) = get_rel_size(&self.relsize_cache, rel) {
+            CacheResult::Found(nblocks)
+        } else {
+            let lsn = Lsn(self.shared.global_lw_lsn.load(Ordering::Relaxed));
+            CacheResult::NotFound(lsn)
+        }
+    }
+
+    pub async fn get_page(
+        &'t self,
+        rel: &RelTag,
+        block_number: u32,
+        dst: impl uring_common::buf::IoBufMut + Send + Sync,
+    ) -> Result<CacheResult<()>, std::io::Error> {
+        let x = if let Some(block_entry) = self.block_map.get(&BlockKey::from((rel, block_number)))
+        {
+            block_entry.referenced.store(true, Ordering::Relaxed);
+
+            let cache_block = block_entry.cache_block.load(Ordering::Relaxed);
+            if cache_block != INVALID_CACHE_BLOCK {
+                // pin it and release lock
+                block_entry.pinned.fetch_add(1, Ordering::Relaxed);
+
+                (cache_block, DeferredUnpin(block_entry.pinned.as_ptr()))
+            } else {
+                return Ok(CacheResult::NotFound(block_entry.lw_lsn.load()));
+            }
+        } else {
+            let lsn = Lsn(self.shared.global_lw_lsn.load(Ordering::Relaxed));
+            return Ok(CacheResult::NotFound(lsn));
+        };
+
+        let (cache_block, _deferred_pin) = x;
+        self.file_cache
+            .as_ref()
+            .unwrap()
+            .read_block(cache_block, dst)
+            .await?;
+
+        // unpin the entry (by implicitly dropping deferred_pin)
+        Ok(CacheResult::Found(()))
+    }
+
+    pub async fn page_is_cached(
+        &'t self,
+        rel: &RelTag,
+        block_number: u32,
+    ) -> Result<CacheResult<()>, std::io::Error> {
+        if let Some(block_entry) = self.block_map.get(&BlockKey::from((rel, block_number))) {
+            // This is used for prefetch requests. Treat the probe as an 'access', to keep it
+            // in cache.
+            block_entry.referenced.store(true, Ordering::Relaxed);
+
+            let cache_block = block_entry.cache_block.load(Ordering::Relaxed);
+
+            if cache_block != INVALID_CACHE_BLOCK {
+                Ok(CacheResult::Found(()))
+            } else {
+                Ok(CacheResult::NotFound(block_entry.lw_lsn.load()))
+            }
+        } else {
+            let lsn = Lsn(self.shared.global_lw_lsn.load(Ordering::Relaxed));
+            Ok(CacheResult::NotFound(lsn))
+        }
+    }
+
+    /// Does the relation exists? CacheResult::NotFound means that the cache doesn't contain that
+    /// information, i.e. we don't know if the relation exists or not.
+    pub fn get_rel_exists(&'t self, rel: &RelTag) -> CacheResult<bool> {
+        // we don't currently cache negative entries, so if the relation is in the cache, it exists
+        if let Some(_rel_entry) = self.relsize_cache.get(&RelKey::from(rel)) {
+            CacheResult::Found(true)
+        } else {
+            let lsn = Lsn(self.shared.global_lw_lsn.load(Ordering::Relaxed));
+            CacheResult::NotFound(lsn)
+        }
+    }
+
+    pub fn get_db_size(&'t self, _db_oid: u32) -> CacheResult<u64> {
+        // TODO: it would be nice to cache database sizes too. Getting the database size
+        // is not a very common operation, but when you do it, it's often interactive, with
+        // e.g. psql \l+ command, so the user will feel the latency.
+
+        // fixme: is this right lsn?
+        let lsn = Lsn(self.shared.global_lw_lsn.load(Ordering::Relaxed));
+        CacheResult::NotFound(lsn)
+    }
+
+    pub fn remember_rel_size(&'t self, rel: &RelTag, nblocks: u32, lsn: Lsn) {
+        match self.relsize_cache.entry(RelKey::from(rel)) {
+            Entry::Vacant(e) => {
+                tracing::trace!("inserting rel entry for {rel:?}, {nblocks} blocks");
+                // FIXME: what to do if we run out of memory? Evict other relation entries?
+                _ = e
+                    .insert(RelEntry {
+                        nblocks: AtomicU32::new(nblocks),
+                        lw_lsn: AtomicLsn::new(lsn.0),
+                    })
+                    .expect("out of memory");
+            }
+            Entry::Occupied(e) => {
+                tracing::trace!("updating rel entry for {rel:?}, {nblocks} blocks");
+                e.get().nblocks.store(nblocks, Ordering::Relaxed);
+                e.get().lw_lsn.store(lsn);
+            }
+        };
+    }
+
+    /// Remember the given page contents in the cache.
+    pub async fn remember_page(
+        &'t self,
+        rel: &RelTag,
+        block_number: u32,
+        src: impl uring_common::buf::IoBuf + Send + Sync,
+        lw_lsn: Lsn,
+        is_write: bool,
+    ) {
+        let key = BlockKey::from((rel, block_number));
+
+        // FIXME: make this work when file cache is disabled. Or make it mandatory
+        let file_cache = self.file_cache.as_ref().unwrap();
+
+        if is_write {
+            // there should be no concurrent IOs. If a backend tries to read the page
+            // at the same time, they may get a torn write. That's the same as with
+            // regular POSIX filesystem read() and write()
+
+            // First check if we have a block in cache already
+            let mut old_cache_block = None;
+            let mut found_existing = false;
+
+            // NOTE(quantumish): honoring original semantics here (used to be update_with_fn)
+            // but I don't see any reason why this has to take a write lock.
+            if let Entry::Occupied(e) = self.block_map.entry(key.clone()) {
+                let block_entry = e.get();
+                found_existing = true;
+
+                // Prevent this entry from being evicted
+                let pin_count = block_entry.pinned.fetch_add(1, Ordering::Relaxed);
+                if pin_count > 0 {
+                    // this is unexpected, because the caller has obtained the io-in-progress lock,
+                    // so no one else should try to modify the page at the same time.
+                    // XXX: and I think a read should not be happening either, because the postgres
+                    // buffer is held locked. TODO: check these conditions and tidy this up a little. Seems fragile to just panic.
+                    panic!("block entry was unexpectedly pinned");
+                }
+
+                let cache_block = block_entry.cache_block.load(Ordering::Relaxed);
+                old_cache_block = if cache_block != INVALID_CACHE_BLOCK {
+                    Some(cache_block)
+                } else {
+                    None
+                };
+            }
+
+            // Allocate a new block if required
+            let cache_block = old_cache_block.unwrap_or_else(|| {
+                loop {
+                    if let Some(x) = file_cache.alloc_block() {
+                        break x;
+                    }
+                    if let Some(x) = self.try_evict_cache_block() {
+                        break x;
+                    }
+                }
+            });
+
+            // Write the page to the cache file
+            file_cache
+                .write_block(cache_block, src)
+                .await
+                .expect("error writing to cache");
+            // FIXME: handle errors gracefully.
+            // FIXME: unpin the block entry on error
+
+            // Update the block entry
+            loop {
+                let entry = self.block_map.entry(key.clone());
+                assert_eq!(found_existing, matches!(entry, Entry::Occupied(_)));
+                match entry {
+                    Entry::Occupied(e) => {
+                        let block_entry = e.get();
+                        // Update the cache block
+                        let old_blk = block_entry.cache_block.compare_exchange(
+                            INVALID_CACHE_BLOCK,
+                            cache_block,
+                            Ordering::Relaxed,
+                            Ordering::Relaxed,
+                        );
+                        assert!(old_blk == Ok(INVALID_CACHE_BLOCK) || old_blk == Err(cache_block));
+
+                        block_entry.lw_lsn.store(lw_lsn);
+
+                        block_entry.referenced.store(true, Ordering::Relaxed);
+
+                        let pin_count = block_entry.pinned.fetch_sub(1, Ordering::Relaxed);
+                        assert!(pin_count > 0);
+                        break;
+                    }
+                    Entry::Vacant(e) => {
+                        if e.insert(BlockEntry {
+                            lw_lsn: AtomicLsn::new(lw_lsn.0),
+                            cache_block: AtomicU64::new(cache_block),
+                            pinned: AtomicU64::new(0),
+                            referenced: AtomicBool::new(true),
+                        })
+                        .is_ok()
+                        {
+                            break;
+                        } else {
+                            // The hash map was full. Evict an entry and retry.
+                        }
+                    }
+                }
+                self.try_evict_block_entry();
+            }
+        } else {
+            // !is_write
+            //
+            // We can assume that it doesn't already exist, because the
+            // caller is assumed to have already checked it, and holds
+            // the io-in-progress lock. (The BlockEntry might exist, but no cache block)
+
+            // Allocate a new block first
+            let cache_block = {
+                loop {
+                    if let Some(x) = file_cache.alloc_block() {
+                        break x;
+                    }
+                    if let Some(x) = self.try_evict_cache_block() {
+                        break x;
+                    }
+                }
+            };
+
+            // Write the page to the cache file
+            file_cache
+                .write_block(cache_block, src)
+                .await
+                .expect("error writing to cache");
+            // FIXME: handle errors gracefully.
+
+            loop {
+                match self.block_map.entry(key.clone()) {
+                    Entry::Occupied(e) => {
+                        let block_entry = e.get();
+                        // FIXME: could there be concurrent readers?
+                        assert!(block_entry.pinned.load(Ordering::Relaxed) == 0);
+
+                        let old_cache_block =
+                            block_entry.cache_block.swap(cache_block, Ordering::Relaxed);
+                        if old_cache_block != INVALID_CACHE_BLOCK {
+                            panic!(
+                                "remember_page called in !is_write mode, but page is already cached at blk {old_cache_block}"
+                            );
+                        }
+                        break;
+                    }
+                    Entry::Vacant(e) => {
+                        if e.insert(BlockEntry {
+                            lw_lsn: AtomicLsn::new(lw_lsn.0),
+                            cache_block: AtomicU64::new(cache_block),
+                            pinned: AtomicU64::new(0),
+                            referenced: AtomicBool::new(true),
+                        })
+                        .is_ok()
+                        {
+                            break;
+                        } else {
+                            // The hash map was full. Evict an entry and retry.
+                        }
+                    }
+                };
+
+                self.try_evict_block_entry();
+            }
+        }
+    }
+
+    /// Forget information about given relation in the cache. (For DROP TABLE and such)
+    pub fn forget_rel(&'t self, rel: &RelTag, _nblocks: Option<u32>, flush_lsn: Lsn) {
+        tracing::trace!("forgetting rel entry for {rel:?}");
+        self.relsize_cache.remove(&RelKey::from(rel));
+
+        // update with flush LSN
+        let _ = self
+            .shared
+            .global_lw_lsn
+            .fetch_max(flush_lsn.0, Ordering::Relaxed);
+
+        // also forget all cached blocks for the relation
+        // FIXME
+        /*
+            let mut iter = MapIterator::new(&key_range_for_rel_blocks(rel));
+            let r = self.cache_tree.start_read();
+            while let Some((k, _v)) = iter.next(&r) {
+                let w = self.cache_tree.start_write();
+
+                let mut evicted_cache_block = None;
+
+                let res = w.update_with_fn(&k, |e| {
+                    if let Some(e) = e {
+                        let block_entry = if let MapEntry::Block(e) = e {
+                            e
+                        } else {
+                            panic!("unexpected map entry type for block key");
+                        };
+                        let cache_block = block_entry
+                            .cache_block
+                            .swap(INVALID_CACHE_BLOCK, Ordering::Relaxed);
+                        if cache_block != INVALID_CACHE_BLOCK {
+                            evicted_cache_block = Some(cache_block);
+                        }
+                        UpdateAction::Remove
+                    } else {
+                        UpdateAction::Nothing
+                    }
+                });
+
+                // FIXME: It's pretty surprising to run out of memory while removing. But
+                // maybe it can happen because of trying to shrink a node?
+                res.expect("out of memory");
+
+                if let Some(evicted_cache_block) = evicted_cache_block {
+                    self.file_cache
+                        .as_ref()
+                        .unwrap()
+                        .dealloc_block(evicted_cache_block);
+                }
+        }
+
+            */
+    }
+
+    // Maintenance routines
+
+    /// Evict one block entry from the cache.
+    ///
+    /// This is called when the hash map is full, to make an entry available for a new
+    /// insertion. There's no guarantee that the entry is free by the time this function
+    /// returns anymore; it can taken by a concurrent thread at any time. So you need to
+    /// call this and retry repeatedly until you succeed.
+    fn try_evict_block_entry(&self) {
+        let num_buckets = self.block_map.get_num_buckets();
+        loop {
+            self.metrics.clock_iterations_counter.inc();
+            let victim_bucket = self.clock_hand.fetch_add(1, Ordering::Relaxed) % num_buckets;
+
+            let evict_this = match self.block_map.get_at_bucket(victim_bucket).as_deref() {
+                None => {
+                    // The caller wants to have a free bucket. If there's one already, we're good.
+                    return;
+                }
+                Some((_, blk_entry)) => {
+                    // Clear the 'referenced' flag. If it was already clear,
+                    // release the lock (by exiting this scope), and try to
+                    // evict it.
+                    !blk_entry.referenced.swap(false, Ordering::Relaxed)
+                }
+            };
+            if evict_this {
+                match self.try_evict_entry(victim_bucket) {
+                    EvictResult::Pinned => {
+                        // keep looping
+                    }
+                    EvictResult::Vacant => {
+                        // This was released by someone else. Return so that
+                        // the caller will try to use it. (Chances are that it
+                        // will be reused by someone else, but let's try.)
+                        return;
+                    }
+                    EvictResult::Evicted(None) => {
+                        // This is now free.
+                        return;
+                    }
+                    EvictResult::Evicted(Some(cache_block)) => {
+                        // This is now free. We must not leak the cache block, so put it to the freelist
+                        self.file_cache.as_ref().unwrap().dealloc_block(cache_block);
+                        return;
+                    }
+                }
+            }
+            // TODO: add some kind of a backstop to error out if we loop
+            // too many times without finding any unpinned entries
+        }
+    }
+
+    /// Evict one block from the file cache. This is called when the file cache fills up,
+    /// to release a cache block.
+    ///
+    /// Returns the evicted block. It's not put to the free list, so it's available for
+    /// the caller to use immediately.
+    fn try_evict_cache_block(&self) -> Option<CacheBlock> {
+        let num_buckets = self.block_map.get_num_buckets();
+        let mut iterations = 0;
+        while iterations < 100 {
+            self.metrics.clock_iterations_counter.inc();
+            let victim_bucket = self.clock_hand.fetch_add(1, Ordering::Relaxed) % num_buckets;
+
+            let evict_this = match self.block_map.get_at_bucket(victim_bucket).as_deref() {
+                None => {
+                    // This bucket was unused. It's no use for finding a free cache block
+                    continue;
+                }
+                Some((_, blk_entry)) => {
+                    // Clear the 'referenced' flag. If it was already clear,
+                    // release the lock (by exiting this scope), and try to
+                    // evict it.
+                    !blk_entry.referenced.swap(false, Ordering::Relaxed)
+                }
+            };
+
+            if evict_this {
+                match self.try_evict_entry(victim_bucket) {
+                    EvictResult::Pinned => {
+                        // keep looping
+                    }
+                    EvictResult::Vacant => {
+                        // This was released by someone else. Keep looping.
+                    }
+                    EvictResult::Evicted(None) => {
+                        // This is now free, but it didn't have a cache block
+                        // associated with it. Keep looping.
+                    }
+                    EvictResult::Evicted(Some(cache_block)) => {
+                        // Reuse this
+                        return Some(cache_block);
+                    }
+                }
+            }
+
+            iterations += 1;
+        }
+
+        // Reached the max iteration count without finding an entry. Return
+        // to give the caller a chance to do other things
+        None
+    }
+
+    /// Returns Err, if the page could not be evicted because it was pinned
+    fn try_evict_entry(&self, victim: usize) -> EvictResult {
+        // grab the write lock
+        if let Some(e) = self.block_map.entry_at_bucket(victim) {
+            let old = e.get();
+            // note: all the accesses to 'pinned' currently happen
+            // within update_with_fn(), or while holding ValueReadGuard, which protects from concurrent
+            // updates. Otherwise, another thread could set the 'pinned'
+            // flag just after we have checked it here.
+            //
+            // FIXME: ^^ outdated comment, update_with_fn() is no more
+
+            if old.pinned.load(Ordering::Relaxed) == 0 {
+                let old_val = e.remove();
+                let _ = self
+                    .shared
+                    .global_lw_lsn
+                    .fetch_max(old_val.lw_lsn.into_inner().0, Ordering::Relaxed);
+                let evicted_cache_block = match old_val.cache_block.into_inner() {
+                    INVALID_CACHE_BLOCK => None,
+                    n => Some(n),
+                };
+                if evicted_cache_block.is_some() {
+                    self.metrics.cache_page_evictions_counter.inc();
+                }
+                self.metrics.block_entry_evictions_counter.inc();
+                EvictResult::Evicted(evicted_cache_block)
+            } else {
+                EvictResult::Pinned
+            }
+        } else {
+            EvictResult::Vacant
+        }
+    }
+
+    /// Resize the local file cache.
+    pub fn resize_file_cache(&self, num_blocks: u32) {
+        let old_num_blocks = self.block_map.get_num_buckets() as u32;
+
+        if old_num_blocks < num_blocks {
+            if let Err(err) = self.block_map.grow(num_blocks) {
+                tracing::warn!(
+                    "could not grow file cache to {} blocks (old size {}): {}",
+                    num_blocks,
+                    old_num_blocks,
+                    err
+                );
+            }
+        } else {
+            // TODO: Shrinking not implemented yet
+        }
+    }
+
+    pub fn dump_map(&self, _dst: &mut dyn std::io::Write) {
+        //FIXME self.cache_map.start_read().dump(dst);
+    }
+}
+
+impl<T: metric::group::Encoding> MetricGroup<T> for IntegratedCacheWriteAccess<'_>
+where
+    CounterState: MetricEncoding<T>,
+    GaugeState: MetricEncoding<T>,
+{
+    fn collect_group_into(&self, enc: &mut T) -> Result<(), <T as metric::group::Encoding>::Err> {
+        // Update gauges
+        self.metrics
+            .block_map_num_buckets
+            .set(self.block_map.get_num_buckets() as i64);
+        self.metrics
+            .block_map_num_buckets_in_use
+            .set(self.block_map.get_num_buckets_in_use() as i64);
+        self.metrics
+            .relsize_cache_num_buckets
+            .set(self.relsize_cache.get_num_buckets() as i64);
+        self.metrics
+            .relsize_cache_num_buckets_in_use
+            .set(self.relsize_cache.get_num_buckets_in_use() as i64);
+
+        if let Some(file_cache) = &self.file_cache {
+            file_cache.collect_group_into(enc)?;
+        }
+
+        self.metrics.collect_group_into(enc)
+    }
+}
+
+/// Read relation size from the cache.
+///
+/// This is in a separate function so that it can be shared by
+/// IntegratedCacheReadAccess::get_rel_size() and IntegratedCacheWriteAccess::get_rel_size()
+fn get_rel_size(
+    r: &neon_shmem::hash::HashMapAccess<RelKey, RelEntry>,
+    rel: &RelTag,
+) -> Option<u32> {
+    if let Some(rel_entry) = r.get(&RelKey::from(rel)) {
+        let nblocks = rel_entry.nblocks.load(Ordering::Relaxed);
+        if nblocks != u32::MAX {
+            Some(nblocks)
+        } else {
+            None
+        }
+    } else {
+        None
+    }
+}
+
+pub enum GetBucketResult {
+    Occupied(RelTag, u32),
+    Vacant,
+    OutOfBounds,
+}
+
+/// Accessor for other backends
+///
+/// This allows backends to read pages from the cache directly, on their own, without making a
+/// request to the communicator process.
+impl<'t> IntegratedCacheReadAccess<'t> {
+    pub fn get_rel_size(&'t self, rel: &RelTag) -> Option<u32> {
+        get_rel_size(&self.relsize_cache, rel)
+    }
+
+    pub fn start_read_op(&'t self) -> BackendCacheReadOp<'t> {
+        BackendCacheReadOp {
+            read_guards: Vec::new(),
+            map_access: self,
+        }
+    }
+
+    /// Check if LFC contains the given buffer, and update its last-written LSN if not.
+    ///
+    /// Returns:
+    ///   true if the block is in the LFC
+    ///   false if it's not.
+    ///
+    /// If the block was not in the LFC (i.e. when this returns false), the last-written LSN
+    /// value on the block is updated to the given 'lsn', so that the next read of the block
+    /// will read the new version. Otherwise the caller is assumed to modify the page and
+    /// to update the last-written LSN later by writing the new page.
+    pub fn update_lw_lsn_for_block_if_not_cached(
+        &'t self,
+        rel: &RelTag,
+        block_number: u32,
+        lsn: Lsn,
+    ) -> bool {
+        let key = BlockKey::from((rel, block_number));
+        let entry = self.block_map.entry(key);
+        match entry {
+            Entry::Occupied(e) => {
+                let block_entry = e.get();
+                if block_entry.cache_block.load(Ordering::Relaxed) != INVALID_CACHE_BLOCK {
+                    block_entry.referenced.store(true, Ordering::Relaxed);
+                    true
+                } else {
+                    let old_lwlsn = block_entry.lw_lsn.fetch_max(lsn);
+                    if old_lwlsn >= lsn {
+                        // shouldn't happen
+                        tracing::warn!(
+                            "attempted to move last-written LSN backwards from {old_lwlsn} to {lsn} for rel {rel} blk {block_number}"
+                        );
+                    }
+                    false
+                }
+            }
+            Entry::Vacant(e) => {
+                if e.insert(BlockEntry {
+                    lw_lsn: AtomicLsn::new(lsn.0),
+                    cache_block: AtomicU64::new(INVALID_CACHE_BLOCK),
+                    pinned: AtomicU64::new(0),
+                    referenced: AtomicBool::new(true),
+                })
+                .is_ok()
+                {
+                    false
+                } else {
+                    // The hash table is full.
+                    //
+                    // TODO: Evict something. But for now, just set the global lw LSN instead.
+                    // That's correct, but not very efficient for future reads
+                    let _ = self
+                        .shared
+                        .global_lw_lsn
+                        .fetch_max(lsn.0, Ordering::Relaxed);
+                    false
+                }
+            }
+        }
+    }
+
+    pub fn get_bucket(&self, bucket_no: usize) -> GetBucketResult {
+        match self.block_map.get_at_bucket(bucket_no).as_deref() {
+            None => {
+                // free bucket, or out of bounds
+                if bucket_no >= self.block_map.get_num_buckets() {
+                    GetBucketResult::OutOfBounds
+                } else {
+                    GetBucketResult::Vacant
+                }
+            }
+            Some((key, _)) => GetBucketResult::Occupied(key.rel, key.block_number),
+        }
+    }
+
+    pub fn get_num_buckets_in_use(&self) -> usize {
+        self.block_map.get_num_buckets_in_use()
+    }
+}
+
+pub struct BackendCacheReadOp<'t> {
+    read_guards: Vec<DeferredUnpin>,
+    map_access: &'t IntegratedCacheReadAccess<'t>,
+}
+
+impl<'e> BackendCacheReadOp<'e> {
+    /// Initiate a read of the page from the cache.
+    ///
+    /// This returns the "cache block number", i.e. the block number within the cache file, where
+    /// the page's contents is stored. To get the page contents, the caller needs to read that block
+    /// from the cache file. This returns a guard object that you must hold while it performs the
+    /// read. It's possible that while you are performing the read, the cache block is invalidated.
+    /// After you have completed the read, call BackendCacheReadResult::finish() to check if the
+    /// read was in fact valid or not. If it was concurrently invalidated, you need to retry.
+    pub fn get_page(&mut self, rel: &RelTag, block_number: u32) -> Option<u64> {
+        if let Some(block_entry) = self
+            .map_access
+            .block_map
+            .get(&BlockKey::from((rel, block_number)))
+        {
+            block_entry.referenced.store(true, Ordering::Relaxed);
+
+            let cache_block = block_entry.cache_block.load(Ordering::Relaxed);
+            if cache_block != INVALID_CACHE_BLOCK {
+                block_entry.pinned.fetch_add(1, Ordering::Relaxed);
+                self.read_guards
+                    .push(DeferredUnpin(block_entry.pinned.as_ptr()));
+                Some(cache_block)
+            } else {
+                None
+            }
+        } else {
+            None
+        }
+    }
+
+    pub fn finish(self) -> bool {
+        // TODO: currently, we hold a pin on the in-memory map, so concurrent invalidations are not
+        // possible. But if we switch to optimistic locking, this would return 'false' if the
+        // optimistic locking failed and you need to retry.
+        true
+    }
+}
+
+/// A hack to decrement an AtomicU64 on drop. This is used to decrement the pin count
+/// of a BlockEntry. The safety depends on the fact that the BlockEntry is not evicted
+/// or moved while it's pinned.
+struct DeferredUnpin(*mut u64);
+
+unsafe impl Sync for DeferredUnpin {}
+unsafe impl Send for DeferredUnpin {}
+
+impl Drop for DeferredUnpin {
+    fn drop(&mut self) {
+        // unpin it
+        unsafe {
+            let pin_ref = AtomicU64::from_ptr(self.0);
+            pin_ref.fetch_sub(1, Ordering::Relaxed);
+        }
+    }
+}

pgxn/neon/communicator/src/lib.rs

@@ -1,5 +1,29 @@
+//! Three main parts:
+//! - async tokio communicator core, which receives requests and processes them.
+//! - Main loop and requests queues, which routes requests from backends to the core
+//! - the per-backend glue code, which submits requests
+
+mod backend_comms;
+
+// mark this 'pub', because these functions are called from C code. Otherwise, the compiler
+// complains about a bunch of structs and enum variants being unused, because it thinkgs
+// the functions that use them are never called. There are some C-callable functions in
+// other modules too, but marking this as pub is currently enough to silence the warnings
+//
+// TODO: perhaps collect *all* the extern "C" functions to one module?
+pub mod backend_interface;
+
+mod file_cache;
+mod init;
+mod integrated_cache;
+mod neon_request;
 mod worker_process;
 
+mod global_allocator;
+
 /// Name of the Unix Domain Socket that serves the metrics, and other APIs in the
 /// future. This is within the Postgres data directory.
 const NEON_COMMUNICATOR_SOCKET_NAME: &str = "neon-communicator.socket";
+
+// FIXME: get this from postgres headers somehow
+pub const BLCKSZ: usize = 8192;

pgxn/neon/communicator/src/neon_request.rs

@@ -0,0 +1,466 @@
+// Definitions of some core PostgreSQL datatypes.
+
+/// XLogRecPtr is defined in "access/xlogdefs.h" as:
+///
+/// ```
+/// typedef uint64 XLogRecPtr;
+/// ```
+/// cbindgen:no-export
+pub type XLogRecPtr = u64;
+
+pub type CLsn = XLogRecPtr;
+pub type COid = u32;
+
+// This conveniently matches PG_IOV_MAX
+pub const MAX_GETPAGEV_PAGES: usize = 32;
+
+pub const INVALID_BLOCK_NUMBER: u32 = u32::MAX;
+
+use std::ffi::CStr;
+
+use pageserver_page_api::{self as page_api, SlruKind};
+
+/// Request from a Postgres backend to the communicator process
+#[allow(clippy::large_enum_variant)]
+#[repr(C)]
+#[derive(Copy, Clone, Debug, strum_macros::EnumDiscriminants)]
+#[strum_discriminants(derive(measured::FixedCardinalityLabel))]
+pub enum NeonIORequest {
+    Empty,
+
+    // Read requests. These are C-friendly variants of the corresponding structs in
+    // pageserver_page_api.
+    RelSize(CRelSizeRequest),
+    GetPageV(CGetPageVRequest),
+    ReadSlruSegment(CReadSlruSegmentRequest),
+    PrefetchV(CPrefetchVRequest),
+    DbSize(CDbSizeRequest),
+
+    /// This is like GetPageV, but bypasses the LFC and allows specifiying the
+    /// request LSNs directly. For debugging purposes only.
+    GetPageVUncached(CGetPageVUncachedRequest),
+
+    // Write requests. These are needed to keep the relation size cache and LFC up-to-date.
+    // They are not sent to the pageserver.
+    WritePage(CWritePageRequest),
+    RelExtend(CRelExtendRequest),
+    RelZeroExtend(CRelZeroExtendRequest),
+    RelCreate(CRelCreateRequest),
+    RelTruncate(CRelTruncateRequest),
+    RelUnlink(CRelUnlinkRequest),
+
+    // Other requests
+    UpdateCachedRelSize(CUpdateCachedRelSizeRequest),
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub enum NeonIOResult {
+    Empty,
+    /// InvalidBlockNumber == 0xffffffff means "rel does not exist"
+    RelSize(u32),
+
+    /// the result pages are written to the shared memory addresses given in the request
+    GetPageV,
+    /// The result is written to the file, path to which is provided
+    /// in the request. The [`u64`] value here is the number of blocks.
+    ReadSlruSegment(u64),
+
+    /// A prefetch request returns as soon as the request has been received by the communicator.
+    /// It is processed in the background.
+    PrefetchVLaunched,
+
+    DbSize(u64),
+
+    // FIXME design compact error codes. Can't easily pass a string or other dynamic data.
+    // currently, this is 'errno'
+    Error(i32),
+
+    Aborted,
+
+    /// used for all write requests
+    WriteOK,
+}
+
+impl NeonIORequest {
+    /// All requests include a unique request ID, which can be used to trace the execution
+    /// of a request all the way to the pageservers. The request ID needs to be unique
+    /// within the lifetime of the Postgres instance (but not across servers or across
+    /// restarts of the same server).
+    pub fn request_id(&self) -> u64 {
+        use NeonIORequest::*;
+        match self {
+            Empty => 0,
+            RelSize(req) => req.request_id,
+            GetPageV(req) => req.request_id,
+            GetPageVUncached(req) => req.request_id,
+            ReadSlruSegment(req) => req.request_id,
+            PrefetchV(req) => req.request_id,
+            DbSize(req) => req.request_id,
+            WritePage(req) => req.request_id,
+            RelExtend(req) => req.request_id,
+            RelZeroExtend(req) => req.request_id,
+            RelCreate(req) => req.request_id,
+            RelTruncate(req) => req.request_id,
+            RelUnlink(req) => req.request_id,
+            UpdateCachedRelSize(req) => req.request_id,
+        }
+    }
+}
+
+/// Special quick result to a CGetPageVRequest request, indicating that the
+/// the requested pages are present in the local file cache. The backend can
+/// read the blocks directly from the given LFC blocks.
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CCachedGetPageVResult {
+    pub cache_block_numbers: [u64; MAX_GETPAGEV_PAGES],
+}
+
+/// ShmemBuf represents a buffer in shared memory.
+///
+/// SAFETY: The pointer must point to an area in shared memory. The functions allow you to liberally
+/// get a mutable pointer to the contents; it is the caller's responsibility to ensure that you
+/// don't access a buffer that's you're not allowed to. Inappropriate access to the buffer doesn't
+/// violate Rust's safety semantics, but it will mess up and crash Postgres.
+///
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct ShmemBuf {
+    // Pointer to where the result is written or where to read from. Must point into a buffer in shared memory!
+    pub ptr: *mut u8,
+}
+
+unsafe impl Send for ShmemBuf {}
+unsafe impl Sync for ShmemBuf {}
+
+unsafe impl uring_common::buf::IoBuf for ShmemBuf {
+    fn stable_ptr(&self) -> *const u8 {
+        self.ptr
+    }
+
+    fn bytes_init(&self) -> usize {
+        crate::BLCKSZ
+    }
+
+    fn bytes_total(&self) -> usize {
+        crate::BLCKSZ
+    }
+}
+
+unsafe impl uring_common::buf::IoBufMut for ShmemBuf {
+    fn stable_mut_ptr(&mut self) -> *mut u8 {
+        self.ptr
+    }
+
+    unsafe fn set_init(&mut self, pos: usize) {
+        if pos > crate::BLCKSZ {
+            panic!(
+                "set_init called past end of buffer, pos {}, buffer size {}",
+                pos,
+                crate::BLCKSZ
+            );
+        }
+    }
+}
+
+impl ShmemBuf {
+    pub fn as_mut_ptr(&self) -> *mut u8 {
+        self.ptr
+    }
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CRelSizeRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub allow_missing: bool,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CGetPageVRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+    pub nblocks: u8,
+
+    // These fields define where the result is written. Must point into a buffer in shared memory!
+    pub dest: [ShmemBuf; MAX_GETPAGEV_PAGES],
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CGetPageVUncachedRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+    pub nblocks: u8,
+
+    pub request_lsn: CLsn,
+    pub not_modified_since: CLsn,
+
+    // These fields define where the result is written. Must point into a buffer in shared memory!
+    pub dest: [ShmemBuf; MAX_GETPAGEV_PAGES],
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CReadSlruSegmentRequest {
+    pub request_id: u64,
+    pub slru_kind: SlruKind,
+    pub segment_number: u32,
+    pub request_lsn: CLsn,
+    /// Must be a null-terminated C string containing the file path
+    /// where the communicator will write the SLRU segment.
+    pub destination_file_path: ShmemBuf,
+}
+
+impl CReadSlruSegmentRequest {
+    /// Returns the file path where the communicator will write the
+    /// SLRU segment.
+    pub(crate) fn destination_file_path(&self) -> String {
+        unsafe { CStr::from_ptr(self.destination_file_path.as_mut_ptr() as *const _) }
+            .to_string_lossy()
+            .into_owned()
+    }
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CPrefetchVRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+    pub nblocks: u8,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CDbSizeRequest {
+    pub request_id: u64,
+    pub db_oid: COid,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CWritePageRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+    pub lsn: CLsn,
+
+    // `src` defines the new page contents. Must point into a buffer in shared memory!
+    pub src: ShmemBuf,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CRelExtendRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+    pub lsn: CLsn,
+
+    // `src` defines the new page contents. Must point into a buffer in shared memory!
+    pub src: ShmemBuf,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CRelZeroExtendRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub block_number: u32,
+    pub nblocks: u32,
+    pub lsn: CLsn,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CRelCreateRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub lsn: CLsn,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CRelTruncateRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub nblocks: u32,
+    pub lsn: CLsn,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CRelUnlinkRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub lsn: CLsn,
+}
+
+impl CRelSizeRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CGetPageVRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CGetPageVUncachedRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CPrefetchVRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CWritePageRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CRelExtendRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CRelZeroExtendRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CRelCreateRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CRelTruncateRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+impl CRelUnlinkRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug)]
+pub struct CUpdateCachedRelSizeRequest {
+    pub request_id: u64,
+    pub spc_oid: COid,
+    pub db_oid: COid,
+    pub rel_number: u32,
+    pub fork_number: u8,
+    pub nblocks: u32,
+    pub lsn: CLsn,
+}
+
+impl CUpdateCachedRelSizeRequest {
+    pub fn reltag(&self) -> page_api::RelTag {
+        page_api::RelTag {
+            spcnode: self.spc_oid,
+            dbnode: self.db_oid,
+            relnode: self.rel_number,
+            forknum: self.fork_number,
+        }
+    }
+}

pgxn/neon/communicator/src/worker_process/callbacks.rs

@@ -4,10 +4,13 @@
 //!
 //! These are called from the communicator threads! Careful what you do, most Postgres
 //! functions are not safe to call in that context.
+use utils::lsn::Lsn;
 
 #[cfg(not(test))]
 unsafe extern "C" {
+    pub fn notify_proc_unsafe(procno: std::ffi::c_int);
     pub fn callback_set_my_latch_unsafe();
+    pub fn callback_get_request_lsn_unsafe() -> crate::neon_request::CLsn;
     pub fn callback_get_lfc_metrics_unsafe() -> LfcMetrics;
 }
 
@@ -16,20 +19,36 @@ unsafe extern "C" {
 // package, but the code coverage build still builds these and tries to link with the
 // external C code.)
 #[cfg(test)]
+unsafe fn notify_proc_unsafe(_procno: std::ffi::c_int) {
+    panic!("not usable in unit tests");
+}
+#[cfg(test)]
 unsafe fn callback_set_my_latch_unsafe() {
     panic!("not usable in unit tests");
 }
 #[cfg(test)]
+unsafe fn callback_get_request_lsn_unsafe() -> crate::neon_request::CLsn {
+    panic!("not usable in unit tests");
+}
+#[cfg(test)]
 unsafe fn callback_get_lfc_metrics_unsafe() -> LfcMetrics {
     panic!("not usable in unit tests");
 }
 
 // safe wrappers
 
+pub(super) fn notify_proc(procno: std::ffi::c_int) {
+    unsafe { notify_proc_unsafe(procno) };
+}
+
 pub(super) fn callback_set_my_latch() {
     unsafe { callback_set_my_latch_unsafe() };
 }
 
+pub(super) fn get_request_lsn() -> Lsn {
+    Lsn(unsafe { callback_get_request_lsn_unsafe() })
+}
+
 pub(super) fn callback_get_lfc_metrics() -> LfcMetrics {
     unsafe { callback_get_lfc_metrics_unsafe() }
 }

pgxn/neon/communicator/src/worker_process/control_socket.rs

@@ -19,71 +19,105 @@ use http::StatusCode;
 use http::header::CONTENT_TYPE;
 
 use measured::MetricGroup;
+use measured::metric::MetricEncoding;
+use measured::metric::gauge::GaugeState;
+use measured::metric::group::Encoding;
 use measured::text::BufferedTextEncoder;
 
 use std::io::ErrorKind;
+use std::sync::Arc;
 
 use tokio::net::UnixListener;
 
 use crate::NEON_COMMUNICATOR_SOCKET_NAME;
+use crate::worker_process::lfc_metrics::LfcMetricsCollector;
 use crate::worker_process::main_loop::CommunicatorWorkerProcessStruct;
 
-impl CommunicatorWorkerProcessStruct {
+enum ControlSocketState<'a> {
-    /// Launch the listener
+    Full(&'a CommunicatorWorkerProcessStruct<'a>),
-    pub(crate) async fn launch_control_socket_listener(
+    Legacy(LegacyControlSocketState),
-        &'static self,
+}
-    ) -> Result<(), std::io::Error> {
-        use axum::routing::get;
-        let app = Router::new()
-            .route("/metrics", get(get_metrics))
-            .route("/autoscaling_metrics", get(get_autoscaling_metrics))
-            .route("/debug/panic", get(handle_debug_panic))
-            .with_state(self);
 
-        // If the server is restarted, there might be an old socket still
+struct LegacyControlSocketState {
-        // lying around. Remove it first.
+    pub(crate) lfc_metrics: LfcMetricsCollector,
-        match std::fs::remove_file(NEON_COMMUNICATOR_SOCKET_NAME) {
+}
-            Ok(()) => {
-                tracing::warn!("removed stale control socket");
-            }
-            Err(e) if e.kind() == ErrorKind::NotFound => {}
-            Err(e) => {
-                tracing::error!("could not remove stale control socket: {e:#}");
-                // Try to proceed anyway. It will likely fail below though.
-            }
-        };
-
-        // Create the unix domain socket and start listening on it
-        let listener = UnixListener::bind(NEON_COMMUNICATOR_SOCKET_NAME)?;
-
-        tokio::spawn(async {
-            tracing::info!("control socket listener spawned");
-            axum::serve(listener, app)
-                .await
-                .expect("axum::serve never returns")
-        });
 
+impl<T> MetricGroup<T> for LegacyControlSocketState
+where
+    T: Encoding,
+    GaugeState: MetricEncoding<T>,
+{
+    fn collect_group_into(&self, enc: &mut T) -> Result<(), T::Err> {
+        self.lfc_metrics.collect_group_into(enc)?;
         Ok(())
     }
 }
 
+/// Launch the listener
+pub(crate) async fn launch_listener(
+    worker: Option<&'static CommunicatorWorkerProcessStruct<'static>>,
+) -> Result<(), std::io::Error> {
+    use axum::routing::get;
+
+    let state = match worker {
+        Some(worker) => ControlSocketState::Full(worker),
+        None => ControlSocketState::Legacy(LegacyControlSocketState {
+            lfc_metrics: LfcMetricsCollector,
+        }),
+    };
+
+    let app = Router::new()
+        .route("/metrics", get(get_metrics))
+        .route("/autoscaling_metrics", get(get_autoscaling_metrics))
+        .route("/debug/panic", get(handle_debug_panic))
+        .route("/debug/dump_cache_map", get(dump_cache_map))
+        .with_state(Arc::new(state));
+
+    // If the server is restarted, there might be an old socket still
+    // lying around. Remove it first.
+    match std::fs::remove_file(NEON_COMMUNICATOR_SOCKET_NAME) {
+        Ok(()) => {
+            tracing::warn!("removed stale control socket");
+        }
+        Err(e) if e.kind() == ErrorKind::NotFound => {}
+        Err(e) => {
+            tracing::error!("could not remove stale control socket: {e:#}");
+            // Try to proceed anyway. It will likely fail below though.
+        }
+    };
+
+    // Create the unix domain socket and start listening on it
+    let listener = UnixListener::bind(NEON_COMMUNICATOR_SOCKET_NAME)?;
+
+    tokio::spawn(async {
+        tracing::info!("control socket listener spawned");
+        axum::serve(listener, app)
+            .await
+            .expect("axum::serve never returns")
+    });
+
+    Ok(())
+}
+
 /// Expose all Prometheus metrics.
-async fn get_metrics(State(state): State<&CommunicatorWorkerProcessStruct>) -> Response {
+async fn get_metrics(State(state): State<Arc<ControlSocketState<'_>>>) -> Response {
-    tracing::trace!("/metrics requested");
+    match state.as_ref() {
-    metrics_to_response(&state).await
+        ControlSocketState::Full(worker) => metrics_to_response(&worker).await,
+        ControlSocketState::Legacy(legacy) => metrics_to_response(&legacy).await,
+    }
 }
 
 /// Expose Prometheus metrics, for use by the autoscaling agent.
 ///
 /// This is a subset of all the metrics.
-async fn get_autoscaling_metrics(
+async fn get_autoscaling_metrics(State(state): State<Arc<ControlSocketState<'_>>>) -> Response {
-    State(state): State<&CommunicatorWorkerProcessStruct>,
+    match state.as_ref() {
-) -> Response {
+        ControlSocketState::Full(worker) => metrics_to_response(&worker.lfc_metrics).await,
-    tracing::trace!("/metrics requested");
+        ControlSocketState::Legacy(legacy) => metrics_to_response(&legacy.lfc_metrics).await,
-    metrics_to_response(&state.lfc_metrics).await
+    }
 }
 
-async fn handle_debug_panic(State(_state): State<&CommunicatorWorkerProcessStruct>) -> Response {
+async fn handle_debug_panic(State(_state): State<Arc<ControlSocketState<'_>>>) -> Response {
     panic!("test HTTP handler task panic");
 }
 
@@ -100,3 +134,23 @@ async fn metrics_to_response(metrics: &(dyn MetricGroup<BufferedTextEncoder> + S
         .body(Body::from(enc.finish()))
         .unwrap()
 }
+
+async fn dump_cache_map(State(state): State<Arc<ControlSocketState<'_>>>) -> Response {
+    match state.as_ref() {
+        ControlSocketState::Full(worker) => {
+            let mut buf: Vec<u8> = Vec::new();
+            worker.cache.dump_map(&mut buf);
+
+            Response::builder()
+                .status(StatusCode::OK)
+                .header(CONTENT_TYPE, "application/text")
+                .body(Body::from(buf))
+                .unwrap()
+        }
+        ControlSocketState::Legacy(_) => Response::builder()
+            .status(StatusCode::NOT_FOUND)
+            .header(CONTENT_TYPE, "application/text")
+            .body(Body::from(Vec::new()))
+            .unwrap(),
+    }
+}

pgxn/neon/communicator/src/worker_process/in_progress_ios.rs

@@ -0,0 +1,95 @@
+//! Lock table to ensure that only one IO request is in flight for a given
+//! block (or relation or database metadata) at a time
+
+use std::cmp::Eq;
+use std::hash::Hash;
+use std::sync::Arc;
+
+use tokio::sync::{Mutex, OwnedMutexGuard};
+
+use clashmap::ClashMap;
+use clashmap::Entry;
+
+use pageserver_page_api::RelTag;
+
+#[derive(Clone, Eq, Hash, PartialEq)]
+pub enum RequestInProgressKey {
+    Db(u32),
+    Rel(RelTag),
+    Block(RelTag, u32),
+}
+
+type RequestId = u64;
+
+pub type RequestInProgressTable = MutexHashMap<RequestInProgressKey, RequestId>;
+
+// more primitive locking thingie:
+
+pub struct MutexHashMap<K, V>
+where
+    K: Clone + Eq + Hash,
+{
+    lock_table: ClashMap<K, (V, Arc<Mutex<()>>)>,
+}
+
+pub struct MutexHashMapGuard<'a, K, V>
+where
+    K: Clone + Eq + Hash,
+{
+    pub key: K,
+    map: &'a MutexHashMap<K, V>,
+    mutex: Arc<Mutex<()>>,
+    _guard: OwnedMutexGuard<()>,
+}
+
+impl<'a, K, V> Drop for MutexHashMapGuard<'a, K, V>
+where
+    K: Clone + Eq + Hash,
+{
+    fn drop(&mut self) {
+        let (_old_key, old_val) = self.map.lock_table.remove(&self.key).unwrap();
+        assert!(Arc::ptr_eq(&old_val.1, &self.mutex));
+
+        // the guard will be dropped as we return
+    }
+}
+
+impl<K, V> MutexHashMap<K, V>
+where
+    K: Clone + Eq + Hash,
+    V: std::fmt::Display + Copy,
+{
+    pub fn new() -> MutexHashMap<K, V> {
+        MutexHashMap {
+            lock_table: ClashMap::new(),
+        }
+    }
+
+    pub async fn lock<'a>(&'a self, key: K, val: V) -> MutexHashMapGuard<'a, K, V> {
+        let my_mutex = Arc::new(Mutex::new(()));
+        let my_guard = Arc::clone(&my_mutex).lock_owned().await;
+
+        loop {
+            let (request_id, lock) = match self.lock_table.entry(key.clone()) {
+                Entry::Occupied(e) => {
+                    let e = e.get();
+                    (e.0, Arc::clone(&e.1))
+                }
+                Entry::Vacant(e) => {
+                    e.insert((val, Arc::clone(&my_mutex)));
+                    break;
+                }
+            };
+            tracing::info!("waiting for conflicting IO {request_id} to complete");
+            let _ = lock.lock().await;
+            tracing::info!("conflicting IO {request_id} completed");
+        }
+
+        MutexHashMapGuard {
+            key,
+            map: self,
+            mutex: my_mutex,
+            _guard: my_guard,
+        }
+    }
+}

pgxn/neon/communicator/src/worker_process/main_loop.rs

@@ -1,34 +1,126 @@
+use std::collections::HashMap;
+use std::os::fd::AsRawFd;
+use std::os::fd::OwnedFd;
+use std::path::PathBuf;
 use std::str::FromStr as _;
 
+use crate::backend_comms::NeonIORequestSlot;
+use crate::file_cache::FileCache;
+use crate::global_allocator::MyAllocatorCollector;
+use crate::init::CommunicatorInitStruct;
+use crate::integrated_cache::{CacheResult, IntegratedCacheWriteAccess};
+use crate::neon_request::{CGetPageVRequest, CGetPageVUncachedRequest, CPrefetchVRequest};
+use crate::neon_request::{INVALID_BLOCK_NUMBER, NeonIORequest, NeonIOResult};
+use crate::worker_process::control_socket;
+use crate::worker_process::in_progress_ios::{RequestInProgressKey, RequestInProgressTable};
 use crate::worker_process::lfc_metrics::LfcMetricsCollector;
+use pageserver_client_grpc::{PageserverClient, ShardSpec, ShardStripeSize};
+use pageserver_page_api as page_api;
+
+use tokio::io::AsyncReadExt;
+use tokio_pipe::PipeRead;
+use uring_common::buf::IoBuf;
 
 use measured::MetricGroup;
 use measured::metric::MetricEncoding;
+use measured::metric::counter::CounterState;
 use measured::metric::gauge::GaugeState;
 use measured::metric::group::Encoding;
+use measured::{Gauge, GaugeVec};
 use utils::id::{TenantId, TimelineId};
 
-pub struct CommunicatorWorkerProcessStruct {
+use super::callbacks::{get_request_lsn, notify_proc};
+
+use tracing::{error, info, info_span, trace};
+
+use utils::lsn::Lsn;
+
+pub struct CommunicatorWorkerProcessStruct<'a> {
+    /// Tokio runtime that the main loop and any other related tasks runs in.
     runtime: tokio::runtime::Runtime,
 
+    /// Client to communicate with the pageserver
+    client: PageserverClient,
+
+    /// Request slots that backends use to send IO requests to the communicator.
+    neon_request_slots: &'a [NeonIORequestSlot],
+
+    /// Notification pipe. Backends use this to notify the communicator that a request is waiting to
+    /// be processed in one of the request slots.
+    submission_pipe_read_fd: OwnedFd,
+
+    /// Locking table for all in-progress IO requests.
+    in_progress_table: RequestInProgressTable,
+
+    /// Local File Cache, relation size tracking, last-written LSN tracking
+    pub(crate) cache: IntegratedCacheWriteAccess<'a>,
+
     /*** Metrics ***/
     pub(crate) lfc_metrics: LfcMetricsCollector,
+
+    request_counters: GaugeVec<RequestTypeLabelGroupSet>,
+
+    getpage_cache_misses_counter: Gauge,
+    getpage_cache_hits_counter: Gauge,
+
+    // For the requests that affect multiple blocks, have separate counters for the # of blocks affected
+    request_nblocks_counters: GaugeVec<RequestTypeLabelGroupSet>,
+
+    allocator_metrics: MyAllocatorCollector,
+}
+
+// Define a label group, consisting of 1 or more label values
+#[derive(measured::LabelGroup)]
+#[label(set = RequestTypeLabelGroupSet)]
+struct RequestTypeLabelGroup {
+    request_type: crate::neon_request::NeonIORequestDiscriminants,
+}
+
+impl RequestTypeLabelGroup {
+    fn from_req(req: &NeonIORequest) -> Self {
+        RequestTypeLabelGroup {
+            request_type: req.into(),
+        }
+    }
 }
 
 /// Launch the communicator process's Rust subsystems
+#[allow(clippy::too_many_arguments)]
+pub(super) fn init_legacy() -> Result<(), String> {
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .enable_all()
+        .thread_name("communicator thread")
+        .build()
+        .unwrap();
+
+    // Start the listener on the control socket
+    runtime
+        .block_on(control_socket::launch_listener(None))
+        .map_err(|e| e.to_string())?;
+
+    Box::leak(Box::new(runtime));
+
+    Ok(())
+}
+
+/// Launch the communicator process's Rust subsystems
+#[allow(clippy::too_many_arguments)]
 pub(super) fn init(
-    tenant_id: Option<&str>,
+    cis: CommunicatorInitStruct,
-    timeline_id: Option<&str>,
+    tenant_id: &str,
-) -> Result<&'static CommunicatorWorkerProcessStruct, String> {
+    timeline_id: &str,
+    auth_token: Option<&str>,
+    shard_map: HashMap<utils::shard::ShardIndex, String>,
+    stripe_size: Option<ShardStripeSize>,
+    initial_file_cache_size: u64,
+    file_cache_path: Option<PathBuf>,
+) -> Result<&'static CommunicatorWorkerProcessStruct<'static>, String> {
     // The caller validated these already
-    let _tenant_id = tenant_id
+    let tenant_id = TenantId::from_str(tenant_id).map_err(|e| format!("invalid tenant ID: {e}"))?;
-        .map(TenantId::from_str)
+    let timeline_id =
-        .transpose()
+        TimelineId::from_str(timeline_id).map_err(|e| format!("invalid timeline ID: {e}"))?;
-        .map_err(|e| format!("invalid tenant ID: {e}"))?;
+    let shard_spec =
-    let _timeline_id = timeline_id
+        ShardSpec::new(shard_map, stripe_size).map_err(|e| format!("invalid shard spec: {e}:"))?;
-        .map(TimelineId::from_str)
-        .transpose()
-        .map_err(|e| format!("invalid timeline ID: {e}"))?;
 
     let runtime = tokio::runtime::Builder::new_multi_thread()
         .enable_all()
@@ -36,31 +128,716 @@ pub(super) fn init(
         .build()
         .unwrap();
 
+    let last_lsn = get_request_lsn();
+
+    let file_cache = if let Some(path) = file_cache_path {
+        Some(FileCache::new(&path, initial_file_cache_size).expect("could not create cache file"))
+    } else {
+        // FIXME: temporarily for testing, use LFC even if disabled
+        Some(
+            FileCache::new(&PathBuf::from("new_filecache"), 1000)
+                .expect("could not create cache file"),
+        )
+    };
+
+    // Initialize subsystems
+    let cache = cis
+        .integrated_cache_init_struct
+        .worker_process_init(last_lsn, file_cache);
+
+    let client = {
+        let _guard = runtime.enter();
+        PageserverClient::new(
+            tenant_id,
+            timeline_id,
+            shard_spec,
+            auth_token.map(|s| s.to_string()),
+            None,
+        )
+        .expect("could not create client")
+    };
+
     let worker_struct = CommunicatorWorkerProcessStruct {
         // Note: it's important to not drop the runtime, or all the tasks are dropped
         // too. Including it in the returned struct is one way to keep it around.
         runtime,
+        neon_request_slots: cis.neon_request_slots,
+        client,
+        cache,
+        submission_pipe_read_fd: cis.submission_pipe_read_fd,
+        in_progress_table: RequestInProgressTable::new(),
 
         // metrics
         lfc_metrics: LfcMetricsCollector,
+
+        request_counters: GaugeVec::new(),
+
+        getpage_cache_misses_counter: Gauge::new(),
+        getpage_cache_hits_counter: Gauge::new(),
+
+        request_nblocks_counters: GaugeVec::new(),
+
+        allocator_metrics: MyAllocatorCollector::new(),
     };
+
     let worker_struct = Box::leak(Box::new(worker_struct));
 
+    let main_loop_handle = worker_struct.runtime.spawn(worker_struct.run());
+    worker_struct.runtime.spawn(async {
+        let err = main_loop_handle.await.unwrap_err();
+        error!("error: {err:?}");
+    });
+
     // Start the listener on the control socket
     worker_struct
         .runtime
-        .block_on(worker_struct.launch_control_socket_listener())
+        .block_on(control_socket::launch_listener(Some(worker_struct)))
         .map_err(|e| e.to_string())?;
 
     Ok(worker_struct)
 }
 
-impl<T> MetricGroup<T> for CommunicatorWorkerProcessStruct
+impl<'t> CommunicatorWorkerProcessStruct<'t> {
+    /// Update the configuration
+    pub(super) fn update_shard_map(
+        &self,
+        new_shard_map: HashMap<utils::shard::ShardIndex, String>,
+        stripe_size: Option<ShardStripeSize>,
+    ) {
+        let shard_spec = ShardSpec::new(new_shard_map, stripe_size).expect("invalid shard spec");
+
+        {
+            let _in_runtime = self.runtime.enter();
+            if let Err(err) = self.client.update_shards(shard_spec) {
+                tracing::error!("could not update shard map: {err:?}");
+            }
+        }
+    }
+
+    /// Main loop of the worker process. Receive requests from the backends and process them.
+    pub(super) async fn run(&'static self) {
+        let mut idxbuf: [u8; 4] = [0; 4];
+
+        let mut submission_pipe_read =
+            PipeRead::try_from(self.submission_pipe_read_fd.as_raw_fd()).expect("invalid pipe fd");
+
+        loop {
+            // Wait for a backend to ring the doorbell
+            match submission_pipe_read.read(&mut idxbuf).await {
+                Ok(4) => {}
+                Ok(nbytes) => panic!("short read ({nbytes} bytes) on communicator pipe"),
+                Err(e) => panic!("error reading from communicator pipe: {e}"),
+            }
+            let slot_idx = u32::from_ne_bytes(idxbuf) as usize;
+
+            // Read the IO request from the slot indicated in the wakeup
+            let Some(slot) = self.neon_request_slots[slot_idx].start_processing_request() else {
+                // This currently should not happen. But if we had multiple threads picking up
+                // requests, and without waiting for the notifications, it could.
+                panic!("no request in slot");
+            };
+
+            // Ok, we have ownership of this request now. We must process it now, there's no going
+            // back.
+            //
+            // Spawn a separate task for every request. That's a little excessive for requests that
+            // can be quickly satisfied from the cache, but we expect that to be rare, because the
+            // requesting backend would have already checked the cache.
+            tokio::spawn(async move {
+                use tracing::Instrument;
+
+                let request_id = slot.get_request().request_id();
+                let owner_procno = slot.get_owner_procno();
+
+                let span = info_span!(
+                    "processing",
+                    request_id = request_id,
+                    slot_idx = slot_idx,
+                    procno = owner_procno,
+                );
+                async {
+                    // FIXME: as a temporary hack, abort the request if we don't get a response
+                    // promptly.
+                    //
+                    // Lots of regression tests are getting stuck and failing at the moment,
+                    // this makes them fail a little faster, which it faster to iterate.
+                    // This needs to be removed once more regression tests are passing.
+                    // See also similar hack in the backend code, in wait_request_completion()
+                    let result = tokio::time::timeout(
+                        tokio::time::Duration::from_secs(60),
+                        self.handle_request(slot.get_request()),
+                    )
+                    .await
+                    .unwrap_or_else(|_elapsed| {
+                        info!("request {request_id} timed out");
+                        NeonIOResult::Error(libc::ETIMEDOUT)
+                    });
+                    trace!("request {request_id} at slot {slot_idx} completed");
+
+                    // Ok, we have completed the IO. Mark the request as completed. After that,
+                    // we no longer have ownership of the slot, and must not modify it.
+                    slot.completed(result);
+
+                    // Notify the backend about the completion. (Note that the backend might see
+                    // the completed status even before this; this is just a wakeup)
+                    notify_proc(owner_procno);
+                }
+                .instrument(span)
+                .await
+            });
+        }
+    }
+
+    /// Compute the 'request_lsn' to use for a pageserver request
+    fn request_lsns(&self, not_modified_since_lsn: Lsn) -> page_api::ReadLsn {
+        let mut request_lsn = get_request_lsn();
+
+        // Is it possible that the last-written LSN is ahead of last flush LSN? Generally not, we
+        // shouldn't evict a page from the buffer cache before all its modifications have been
+        // safely flushed. That's the "WAL before data" rule. However, there are a few exceptions:
+        //
+        // - when creation an index: _bt_blwritepage logs the full page without flushing WAL before
+        // smgrextend (files are fsynced before build ends).
+        //
+        // XXX: If we make a request LSN greater than the current WAL flush LSN, the pageserver would
+        // block waiting for the WAL arrive, until we flush it and it propagates through the
+        // safekeepers to the pageserver. If there's nothing that forces the WAL to be flushed,
+        // the pageserver would get stuck waiting forever. To avoid that, all the write-
+        // functions in communicator_new.c call XLogSetAsyncXactLSN(). That nudges the WAL writer to
+        // perform the flush relatively soon.
+        //
+        // It would perhaps be nicer to do the WAL flush here, but it's tricky to call back into
+        // Postgres code to do that from here. That's why we rely on communicator_new.c to do the
+        // calls "pre-emptively".
+        //
+        // FIXME: Because of the above, it can still happen that the flush LSN is ahead of
+        // not_modified_since, if the WAL writer hasn't done the flush yet. It would be nice to know
+        // if there are other cases like that that we have mised, but unfortunately we cannot turn
+        // this into an assertion because of that legit case.
+        //
+        // See also the old logic in neon_get_request_lsns() C function
+        if not_modified_since_lsn > request_lsn {
+            tracing::info!(
+                "not_modified_since_lsn {} is ahead of last flushed LSN {}",
+                not_modified_since_lsn,
+                request_lsn
+            );
+            request_lsn = not_modified_since_lsn;
+        }
+
+        page_api::ReadLsn {
+            request_lsn,
+            not_modified_since_lsn: Some(not_modified_since_lsn),
+        }
+    }
+
+    /// Handle one IO request
+    async fn handle_request(&'static self, request: &'_ NeonIORequest) -> NeonIOResult {
+        self.request_counters
+            .inc(RequestTypeLabelGroup::from_req(request));
+        match request {
+            NeonIORequest::Empty => {
+                error!("unexpected Empty IO request");
+                NeonIOResult::Error(0)
+            }
+            NeonIORequest::RelSize(req) => {
+                let rel = req.reltag();
+
+                let _in_progress_guard = self
+                    .in_progress_table
+                    .lock(RequestInProgressKey::Rel(rel), req.request_id)
+                    .await;
+
+                // Check the cache first
+                let not_modified_since = match self.cache.get_rel_size(&rel) {
+                    CacheResult::Found(nblocks) => {
+                        tracing::trace!("found relsize for {:?} in cache: {}", rel, nblocks);
+                        return NeonIOResult::RelSize(nblocks);
+                    }
+                    // XXX: we don't cache negative entries, so if there's no entry in the cache, it could mean
+                    // that the relation doesn't exist or that we don't have it cached.
+                    CacheResult::NotFound(lsn) => lsn,
+                };
+
+                let read_lsn = self.request_lsns(not_modified_since);
+                match self
+                    .client
+                    .get_rel_size(page_api::GetRelSizeRequest {
+                        read_lsn,
+                        rel,
+                        allow_missing: req.allow_missing,
+                    })
+                    .await
+                {
+                    Ok(Some(nblocks)) => {
+                        // update the cache
+                        tracing::trace!(
+                            "updated relsize for {:?} in cache: {}, lsn {}",
+                            rel,
+                            nblocks,
+                            read_lsn
+                        );
+                        self.cache
+                            .remember_rel_size(&rel, nblocks, not_modified_since);
+
+                        NeonIOResult::RelSize(nblocks)
+                    }
+                    Ok(None) => {
+                        // TODO: cache negative entry?
+                        NeonIOResult::RelSize(INVALID_BLOCK_NUMBER)
+                    }
+                    Err(err) => {
+                        // FIXME: Could we map the tonic StatusCode to a libc errno in a more fine-grained way? Or pass the error message to the backend
+                        info!("tonic error: {err:?}");
+                        NeonIOResult::Error(libc::EIO)
+                    }
+                }
+            }
+            NeonIORequest::GetPageV(req) => match self.handle_get_pagev_request(req).await {
+                Ok(()) => NeonIOResult::GetPageV,
+                Err(errno) => NeonIOResult::Error(errno),
+            },
+            NeonIORequest::GetPageVUncached(req) => {
+                match self.handle_get_pagev_uncached_request(req).await {
+                    Ok(()) => NeonIOResult::GetPageV,
+                    Err(errno) => NeonIOResult::Error(errno),
+                }
+            }
+            NeonIORequest::ReadSlruSegment(req) => {
+                let lsn = Lsn(req.request_lsn);
+                let file_path = req.destination_file_path();
+
+                match self
+                    .client
+                    .get_slru_segment(page_api::GetSlruSegmentRequest {
+                        read_lsn: self.request_lsns(lsn),
+                        kind: req.slru_kind,
+                        segno: req.segment_number,
+                    })
+                    .await
+                {
+                    Ok(slru_bytes) => {
+                        if let Err(e) = tokio::fs::write(&file_path, &slru_bytes).await {
+                            error!("could not write slru segment to file {file_path}: {e}");
+                            return NeonIOResult::Error(e.raw_os_error().unwrap_or(libc::EIO));
+                        }
+
+                        let blocks_count = slru_bytes.len() / crate::BLCKSZ;
+
+                        NeonIOResult::ReadSlruSegment(blocks_count as _)
+                    }
+                    Err(err) => {
+                        // FIXME: Could we map the tonic StatusCode to a libc errno in a more fine-grained way? Or pass the error message to the backend
+                        info!("tonic error: {err:?}");
+                        NeonIOResult::Error(libc::EIO)
+                    }
+                }
+            }
+            NeonIORequest::PrefetchV(req) => {
+                self.request_nblocks_counters
+                    .inc_by(RequestTypeLabelGroup::from_req(request), req.nblocks as i64);
+                let req = *req;
+                // FIXME: handle_request() runs in a separate task already, do we really need to spawn a new one here?
+                tokio::spawn(async move { self.handle_prefetchv_request(&req).await });
+                NeonIOResult::PrefetchVLaunched
+            }
+            NeonIORequest::DbSize(req) => {
+                let _in_progress_guard = self
+                    .in_progress_table
+                    .lock(RequestInProgressKey::Db(req.db_oid), req.request_id)
+                    .await;
+
+                // Check the cache first
+                let not_modified_since = match self.cache.get_db_size(req.db_oid) {
+                    CacheResult::Found(db_size) => {
+                        // get_page already copied the block content to the destination
+                        return NeonIOResult::DbSize(db_size);
+                    }
+                    CacheResult::NotFound(lsn) => lsn,
+                };
+
+                match self
+                    .client
+                    .get_db_size(page_api::GetDbSizeRequest {
+                        read_lsn: self.request_lsns(not_modified_since),
+                        db_oid: req.db_oid,
+                    })
+                    .await
+                {
+                    Ok(db_size) => NeonIOResult::DbSize(db_size),
+                    Err(err) => {
+                        // FIXME: Could we map the tonic StatusCode to a libc errno in a more fine-grained way? Or pass the error message to the backend
+                        info!("tonic error: {err:?}");
+                        NeonIOResult::Error(libc::EIO)
+                    }
+                }
+            }
+
+            // Write requests
+            NeonIORequest::WritePage(req) => {
+                let rel = req.reltag();
+                let _in_progress_guard = self
+                    .in_progress_table
+                    .lock(
+                        RequestInProgressKey::Block(rel, req.block_number),
+                        req.request_id,
+                    )
+                    .await;
+
+                // We must at least update the last-written LSN on the page, but also store the page
+                // image in the LFC while we still have it
+                self.cache
+                    .remember_page(&rel, req.block_number, req.src, Lsn(req.lsn), true)
+                    .await;
+                NeonIOResult::WriteOK
+            }
+            NeonIORequest::RelExtend(req) => {
+                let rel = req.reltag();
+                let _in_progress_guard = self
+                    .in_progress_table
+                    .lock(
+                        RequestInProgressKey::Block(rel, req.block_number),
+                        req.request_id,
+                    )
+                    .await;
+
+                // We must at least update the last-written LSN on the page and the relation size,
+                // but also store the page image in the LFC while we still have it
+                self.cache
+                    .remember_page(&rel, req.block_number, req.src, Lsn(req.lsn), true)
+                    .await;
+                self.cache
+                    .remember_rel_size(&req.reltag(), req.block_number + 1, Lsn(req.lsn));
+                NeonIOResult::WriteOK
+            }
+            NeonIORequest::RelZeroExtend(req) => {
+                self.request_nblocks_counters
+                    .inc_by(RequestTypeLabelGroup::from_req(request), req.nblocks as i64);
+
+                // TODO: need to grab an io-in-progress lock for this? I guess not
+                // TODO: We could put the empty pages to the cache. Maybe have
+                // a marker on the block entries for all-zero pages, instead of
+                // actually storing the empty pages.
+                self.cache.remember_rel_size(
+                    &req.reltag(),
+                    req.block_number + req.nblocks,
+                    Lsn(req.lsn),
+                );
+                NeonIOResult::WriteOK
+            }
+            NeonIORequest::RelCreate(req) => {
+                // TODO: need to grab an io-in-progress lock for this? I guess not
+                self.cache.remember_rel_size(&req.reltag(), 0, Lsn(req.lsn));
+                NeonIOResult::WriteOK
+            }
+            NeonIORequest::RelTruncate(req) => {
+                // TODO: need to grab an io-in-progress lock for this? I guess not
+                self.cache
+                    .remember_rel_size(&req.reltag(), req.nblocks, Lsn(req.lsn));
+                NeonIOResult::WriteOK
+            }
+            NeonIORequest::RelUnlink(req) => {
+                // TODO: need to grab an io-in-progress lock for this? I guess not
+                self.cache.forget_rel(&req.reltag(), None, Lsn(req.lsn));
+                NeonIOResult::WriteOK
+            }
+            NeonIORequest::UpdateCachedRelSize(req) => {
+                // TODO: need to grab an io-in-progress lock for this? I guess not
+                self.cache
+                    .remember_rel_size(&req.reltag(), req.nblocks, Lsn(req.lsn));
+                NeonIOResult::WriteOK
+            }
+        }
+    }
+
+    /// Subroutine to handle a GetPageV request, since it's a little more complicated than
+    /// others.
+    async fn handle_get_pagev_request(&'t self, req: &CGetPageVRequest) -> Result<(), i32> {
+        let rel = req.reltag();
+
+        // Check the cache first
+        //
+        // Note: Because the backends perform a direct lookup in the cache before sending
+        // the request to the communicator process, we expect the pages to almost never
+        // be already in cache. It could happen if:
+        // 1. two backends try to read the same page at the same time, but that should never
+        //    happen because there's higher level locking in the Postgres buffer manager, or
+        // 2. a prefetch request finished at the same time as a backend requested the
+        //    page. That's much more likely.
+        let mut cache_misses = Vec::with_capacity(req.nblocks as usize);
+        for i in 0..req.nblocks {
+            let blkno = req.block_number + i as u32;
+
+            // note: this is deadlock-safe even though we hold multiple locks at the same time,
+            // because they're always acquired in the same order.
+            let in_progress_guard = self
+                .in_progress_table
+                .lock(RequestInProgressKey::Block(rel, blkno), req.request_id)
+                .await;
+
+            let dest = req.dest[i as usize];
+            let not_modified_since = match self.cache.get_page(&rel, blkno, dest).await {
+                Ok(CacheResult::Found(_)) => {
+                    // get_page already copied the block content to the destination
+                    trace!("found blk {} in rel {:?} in LFC", blkno, rel);
+                    continue;
+                }
+                Ok(CacheResult::NotFound(lsn)) => lsn,
+                Err(_io_error) => return Err(libc::EIO), // FIXME print the error?
+            };
+            cache_misses.push((blkno, not_modified_since, dest, in_progress_guard));
+        }
+        self.getpage_cache_misses_counter
+            .inc_by(cache_misses.len() as i64);
+        self.getpage_cache_hits_counter
+            .inc_by(req.nblocks as i64 - cache_misses.len() as i64);
+
+        if cache_misses.is_empty() {
+            return Ok(());
+        }
+        let not_modified_since = cache_misses
+            .iter()
+            .map(|(_blkno, lsn, _dest, _guard)| *lsn)
+            .max()
+            .unwrap();
+
+        // Construct a pageserver request for the cache misses
+        let block_numbers: Vec<u32> = cache_misses
+            .iter()
+            .map(|(blkno, _lsn, _dest, _guard)| *blkno)
+            .collect();
+        let read_lsn = self.request_lsns(not_modified_since);
+        trace!(
+            "sending getpage request for blocks {:?} in rel {:?} lsns {}",
+            block_numbers, rel, read_lsn
+        );
+        match self
+            .client
+            .get_page(page_api::GetPageRequest {
+                request_id: req.request_id.into(),
+                request_class: page_api::GetPageClass::Normal,
+                read_lsn,
+                rel,
+                block_numbers: block_numbers.clone(),
+            })
+            .await
+        {
+            Ok(resp) => {
+                // Write the received page images directly to the shared memory location
+                // that the backend requested.
+                if resp.pages.len() != block_numbers.len() {
+                    error!(
+                        "received unexpected response with {} page images from pageserver for a request for {} pages",
+                        resp.pages.len(),
+                        block_numbers.len(),
+                    );
+                    return Err(libc::EIO);
+                }
+
+                trace!(
+                    "received getpage response for blocks {:?} in rel {:?} lsns {}",
+                    block_numbers, rel, read_lsn
+                );
+
+                for (page, (blkno, _lsn, dest, _guard)) in resp.pages.into_iter().zip(cache_misses)
+                {
+                    let src: &[u8] = page.image.as_ref();
+                    let len = std::cmp::min(src.len(), dest.bytes_total());
+                    unsafe {
+                        std::ptr::copy_nonoverlapping(src.as_ptr(), dest.as_mut_ptr(), len);
+                    };
+
+                    // Also store it in the LFC while we have it
+                    self.cache
+                        .remember_page(
+                            &rel,
+                            blkno,
+                            page.image,
+                            read_lsn.not_modified_since_lsn.unwrap(),
+                            false,
+                        )
+                        .await;
+                }
+            }
+            Err(err) => {
+                // FIXME: Could we map the tonic StatusCode to a libc errno in a more fine-grained way? Or pass the error message to the backend
+                info!("tonic error: {err:?}");
+                return Err(libc::EIO);
+            }
+        }
+        Ok(())
+    }
+
+    /// Subroutine to handle an GetPageVUncached request.
+    ///
+    /// Note: this bypasses the cache, in-progress IO locking, and all other side-effects.
+    /// This request type is only used in tests.
+    async fn handle_get_pagev_uncached_request(
+        &'t self,
+        req: &CGetPageVUncachedRequest,
+    ) -> Result<(), i32> {
+        let rel = req.reltag();
+
+        // Construct a pageserver request
+        let block_numbers: Vec<u32> =
+            (req.block_number..(req.block_number + (req.nblocks as u32))).collect();
+        let read_lsn = page_api::ReadLsn {
+            request_lsn: Lsn(req.request_lsn),
+            not_modified_since_lsn: Some(Lsn(req.not_modified_since)),
+        };
+        trace!(
+            "sending (uncached) getpage request for blocks {:?} in rel {:?} lsns {}",
+            block_numbers, rel, read_lsn
+        );
+        match self
+            .client
+            .get_page(page_api::GetPageRequest {
+                request_id: req.request_id.into(),
+                request_class: page_api::GetPageClass::Normal,
+                read_lsn,
+                rel,
+                block_numbers: block_numbers.clone(),
+            })
+            .await
+        {
+            Ok(resp) => {
+                // Write the received page images directly to the shared memory location
+                // that the backend requested.
+                if resp.pages.len() != block_numbers.len() {
+                    error!(
+                        "received unexpected response with {} page images from pageserver for a request for {} pages",
+                        resp.pages.len(),
+                        block_numbers.len(),
+                    );
+                    return Err(libc::EIO);
+                }
+
+                trace!(
+                    "received getpage response for blocks {:?} in rel {:?} lsns {}",
+                    block_numbers, rel, read_lsn
+                );
+
+                for (page, dest) in resp.pages.into_iter().zip(req.dest) {
+                    let src: &[u8] = page.image.as_ref();
+                    let len = std::cmp::min(src.len(), dest.bytes_total());
+                    unsafe {
+                        std::ptr::copy_nonoverlapping(src.as_ptr(), dest.as_mut_ptr(), len);
+                    };
+                }
+            }
+            Err(err) => {
+                // FIXME: Could we map the tonic StatusCode to a libc errno in a more fine-grained way? Or pass the error message to the backend
+                info!("tonic error: {err:?}");
+                return Err(libc::EIO);
+            }
+        }
+        Ok(())
+    }
+
+    /// Subroutine to handle a PrefetchV request, since it's a little more complicated than
+    /// others.
+    ///
+    /// This is very similar to a GetPageV request, but the results are only stored in the cache.
+    async fn handle_prefetchv_request(&'static self, req: &CPrefetchVRequest) -> Result<(), i32> {
+        let rel = req.reltag();
+
+        // Check the cache first
+        let mut cache_misses = Vec::with_capacity(req.nblocks as usize);
+        for i in 0..req.nblocks {
+            let blkno = req.block_number + i as u32;
+
+            // note: this is deadlock-safe even though we hold multiple locks at the same time,
+            // because they're always acquired in the same order.
+            let in_progress_guard = self
+                .in_progress_table
+                .lock(RequestInProgressKey::Block(rel, blkno), req.request_id)
+                .await;
+
+            let not_modified_since = match self.cache.page_is_cached(&rel, blkno).await {
+                Ok(CacheResult::Found(_)) => {
+                    trace!("found blk {} in rel {:?} in LFC", blkno, rel);
+                    continue;
+                }
+                Ok(CacheResult::NotFound(lsn)) => lsn,
+                Err(_io_error) => return Err(libc::EIO), // FIXME print the error?
+            };
+            cache_misses.push((blkno, not_modified_since, in_progress_guard));
+        }
+        if cache_misses.is_empty() {
+            return Ok(());
+        }
+        let not_modified_since = cache_misses
+            .iter()
+            .map(|(_blkno, lsn, _guard)| *lsn)
+            .max()
+            .unwrap();
+        let block_numbers: Vec<u32> = cache_misses
+            .iter()
+            .map(|(blkno, _lsn, _guard)| *blkno)
+            .collect();
+
+        // TODO: spawn separate tasks for these. Use the integrated cache to keep track of the
+        // in-flight requests
+
+        match self
+            .client
+            .get_page(page_api::GetPageRequest {
+                request_id: req.request_id.into(),
+                request_class: page_api::GetPageClass::Prefetch,
+                read_lsn: self.request_lsns(not_modified_since),
+                rel,
+                block_numbers: block_numbers.clone(),
+            })
+            .await
+        {
+            Ok(resp) => {
+                trace!(
+                    "prefetch completed, remembering blocks {:?} in rel {:?} in LFC",
+                    block_numbers, rel
+                );
+                if resp.pages.len() != block_numbers.len() {
+                    error!(
+                        "received unexpected response with {} page images from pageserver for a request for {} pages",
+                        resp.pages.len(),
+                        block_numbers.len(),
+                    );
+                    return Err(libc::EIO);
+                }
+
+                for (page, (blkno, _lsn, _guard)) in resp.pages.into_iter().zip(cache_misses) {
+                    self.cache
+                        .remember_page(&rel, blkno, page.image, not_modified_since, false)
+                        .await;
+                }
+            }
+            Err(err) => {
+                // FIXME: Could we map the tonic StatusCode to a libc errno in a more fine-grained way? Or pass the error message to the backend
+                info!("tonic error: {err:?}");
+                return Err(libc::EIO);
+            }
+        }
+        Ok(())
+    }
+}
+
+impl<T> MetricGroup<T> for CommunicatorWorkerProcessStruct<'_>
 where
     T: Encoding,
+    CounterState: MetricEncoding<T>,
     GaugeState: MetricEncoding<T>,
 {
     fn collect_group_into(&self, enc: &mut T) -> Result<(), T::Err> {
-        self.lfc_metrics.collect_group_into(enc)
+        use measured::metric::MetricFamilyEncoding;
+        use measured::metric::name::MetricName;
+
+        self.lfc_metrics.collect_group_into(enc)?;
+        self.cache.collect_group_into(enc)?;
+        self.request_counters
+            .collect_family_into(MetricName::from_str("request_counters"), enc)?;
+        self.request_nblocks_counters
+            .collect_family_into(MetricName::from_str("request_nblocks_counters"), enc)?;
+        self.allocator_metrics.collect_group_into(enc)?;
+
+        Ok(())
     }
 }

pgxn/neon/communicator/src/worker_process/mod.rs

@@ -4,9 +4,9 @@
 //! - launch the main loop,
 //! - receive IO requests from backends and process them,
 //! - write results back to backends.
-
 mod callbacks;
 mod control_socket;
+mod in_progress_ios;
 mod lfc_metrics;
 mod logging;
 mod main_loop;

pgxn/neon/communicator/src/worker_process/worker_interface.rs

@@ -1,14 +1,21 @@
 //! Functions called from the C code in the worker process
 
+use std::collections::HashMap;
 use std::ffi::{CStr, CString, c_char};
+use std::path::PathBuf;
 
+use crate::init::CommunicatorInitStruct;
 use crate::worker_process::main_loop;
 use crate::worker_process::main_loop::CommunicatorWorkerProcessStruct;
 
+use pageserver_client_grpc::ShardStripeSize;
+
 /// Launch the communicator's tokio tasks, which do most of the work.
 ///
 /// The caller has initialized the process as a regular PostgreSQL background worker
-/// process.
+/// process. The shared memory segment used to communicate with the backends has been
+/// allocated and initialized earlier, at postmaster startup, in
+/// rcommunicator_shmem_init().
 ///
 /// Inputs:
 ///   `tenant_id` and `timeline_id` can be NULL, if we're been launched in "non-Neon" mode,
@@ -23,27 +30,63 @@ use crate::worker_process::main_loop::CommunicatorWorkerProcessStruct;
 /// This is called only once in the process, so the returned struct, and error message in
 /// case of failure, are simply leaked.
 #[unsafe(no_mangle)]
-pub extern "C" fn communicator_worker_launch(
+pub extern "C" fn communicator_worker_process_launch(
+    cis: Box<CommunicatorInitStruct>,
     tenant_id: *const c_char,
     timeline_id: *const c_char,
+    auth_token: *const c_char,
+    shard_map: *mut *mut c_char,
+    nshards: u32,
+    stripe_size: u32,
+    file_cache_path: *const c_char,
+    initial_file_cache_size: u64,
     error_p: *mut *const c_char,
-) -> Option<&'static CommunicatorWorkerProcessStruct> {
+) -> Option<&'static CommunicatorWorkerProcessStruct<'static>> {
+    tracing::warn!("starting threads in rust code");
     // Convert the arguments into more convenient Rust types
-    let tenant_id = if tenant_id.is_null() {
+    let tenant_id = {
+        let cstr = unsafe { CStr::from_ptr(tenant_id) };
+        cstr.to_str().expect("assume UTF-8")
+    };
+    let timeline_id = {
+        let cstr = unsafe { CStr::from_ptr(timeline_id) };
+        cstr.to_str().expect("assume UTF-8")
+    };
+    let auth_token = if auth_token.is_null() {
         None
     } else {
-        let cstr = unsafe { CStr::from_ptr(tenant_id) };
+        let cstr = unsafe { CStr::from_ptr(auth_token) };
         Some(cstr.to_str().expect("assume UTF-8"))
     };
-    let timeline_id = if timeline_id.is_null() {
+    let file_cache_path = {
-        None
+        if file_cache_path.is_null() {
+            None
+        } else {
+            let c_str = unsafe { CStr::from_ptr(file_cache_path) };
+            Some(PathBuf::from(c_str.to_str().unwrap()))
+        }
+    };
+    let shard_map = shard_map_to_hash(nshards, shard_map);
+    // FIXME: distinguish between unsharded, and sharded with 1 shard
+    // Also, we might go from unsharded to sharded while the system
+    // is running.
+    let stripe_size = if stripe_size > 0 && nshards > 1 {
+        Some(ShardStripeSize(stripe_size))
     } else {
-        let cstr = unsafe { CStr::from_ptr(timeline_id) };
+        None
-        Some(cstr.to_str().expect("assume UTF-8"))
     };
 
     // The `init` function does all the work.
-    let result = main_loop::init(tenant_id, timeline_id);
+    let result = main_loop::init(
+        *cis,
+        tenant_id,
+        timeline_id,
+        auth_token,
+        shard_map,
+        stripe_size,
+        initial_file_cache_size,
+        file_cache_path,
+    );
 
     // On failure, return the error message to the C caller in *error_p.
     match result {
@@ -58,3 +101,66 @@ pub extern "C" fn communicator_worker_launch(
         }
     }
 }
+
+#[unsafe(no_mangle)]
+pub extern "C" fn communicator_worker_process_launch_legacy(error_p: *mut *const c_char) -> bool {
+    // The `init` function does all the work.
+    let result = main_loop::init_legacy();
+
+    // On failure, return the error message to the C caller in *error_p.
+    match result {
+        Ok(()) => true,
+        Err(errmsg) => {
+            let errmsg = CString::new(errmsg).expect("no nuls within error message");
+            let errmsg = Box::leak(errmsg.into_boxed_c_str());
+            let p: *const c_char = errmsg.as_ptr();
+
+            unsafe { *error_p = p };
+            false
+        }
+    }
+}
+
+/// Convert the "shard map" from an array of C strings, indexed by shard no to a rust HashMap
+fn shard_map_to_hash(
+    nshards: u32,
+    shard_map: *mut *mut c_char,
+) -> HashMap<utils::shard::ShardIndex, String> {
+    use utils::shard::*;
+
+    assert!(nshards <= u8::MAX as u32);
+
+    let mut result: HashMap<ShardIndex, String> = HashMap::new();
+    let mut p = shard_map;
+
+    for i in 0..nshards {
+        let c_str = unsafe { CStr::from_ptr(*p) };
+
+        p = unsafe { p.add(1) };
+
+        let s = c_str.to_str().unwrap();
+        let k = if nshards > 1 {
+            ShardIndex::new(ShardNumber(i as u8), ShardCount(nshards as u8))
+        } else {
+            ShardIndex::unsharded()
+        };
+        result.insert(k, s.into());
+    }
+    result
+}
+
+/// Inform the rust code about a configuration change
+#[unsafe(no_mangle)]
+pub extern "C" fn communicator_worker_config_reload(
+    proc_handle: &'static CommunicatorWorkerProcessStruct<'static>,
+    file_cache_size: u64,
+    shard_map: *mut *mut c_char,
+    nshards: u32,
+    stripe_size: u32,
+) {
+    proc_handle.cache.resize_file_cache(file_cache_size as u32);
+
+    let shard_map = shard_map_to_hash(nshards, shard_map);
+    let stripe_size = (nshards > 1).then_some(ShardStripeSize(stripe_size));
+    proc_handle.update_shard_map(shard_map, stripe_size);
+}