test_runner: use LFC by default (#8613)

## Problem
LFC is not enabled by default in tests, but it is enabled in production.
This increases the risk of errors in the production environment, which
were not found during the routine workflow.
However, enabling LFC for all the tests may overload the disk on our
servers and increase the number of failures.
So, we try enabling  LFC in one case to evaluate the possible risk.

## Summary of changes
A new environment variable, USE_LFC is introduced. If it is set to true,
LFC is enabled by default in all the tests.
In our workflow, we enable LFC for PG17, release, x86-64, and disabled
for all other combinations.

---------

Co-authored-by: Alexey Masterov <alexeymasterov@neon.tech>
Co-authored-by: a-masterov <72613290+a-masterov@users.noreply.github.com>

.github/workflows/_build-and-test-locally.yml

@@ -19,8 +19,8 @@ on:
         description: 'debug or release'
         required: true
         type: string
-      pg-versions:
-        description: 'a json array of postgres versions to run regression tests on'
+      test-cfg:
+        description: 'a json object of postgres versions and lfc states to run regression tests on'
         required: true
         type: string
 
@@ -276,14 +276,14 @@ jobs:
       options: --init --shm-size=512mb --ulimit memlock=67108864:67108864
     strategy:
       fail-fast: false
-      matrix:
-        pg_version: ${{ fromJson(inputs.pg-versions) }}
+      matrix: ${{ fromJSON(format('{{"include":{0}}}', inputs.test-cfg)) }}
     steps:
       - uses: actions/checkout@v4
         with:
           submodules: true
 
       - name: Pytest regression tests
+        continue-on-error: ${{ matrix.lfc_state == 'with-lfc' }}
         uses: ./.github/actions/run-python-test-set
         timeout-minutes: 60
         with:
@@ -300,6 +300,7 @@ jobs:
           CHECK_ONDISK_DATA_COMPATIBILITY: nonempty
           BUILD_TAG: ${{ inputs.build-tag }}
           PAGESERVER_VIRTUAL_FILE_IO_ENGINE: tokio-epoll-uring
+          USE_LFC: ${{ matrix.lfc_state == 'with-lfc' && 'true' || 'false' }}
 
       # Temporary disable this step until we figure out why it's so flaky
       # Ref https://github.com/neondatabase/neon/issues/4540

.github/workflows/build_and_test.yml

@@ -253,7 +253,14 @@ jobs:
       build-tag: ${{ needs.tag.outputs.build-tag }}
       build-type: ${{ matrix.build-type }}
       # Run tests on all Postgres versions in release builds and only on the latest version in debug builds
-      pg-versions: ${{ matrix.build-type == 'release' && '["v14", "v15", "v16", "v17"]' || '["v17"]' }}
+      # run without LFC on v17 release only
+      test-cfg: |
+        ${{ matrix.build-type == 'release' && '[{"pg_version":"v14", "lfc_state": "without-lfc"},
+                                                {"pg_version":"v15", "lfc_state": "without-lfc"},
+                                                {"pg_version":"v16", "lfc_state": "without-lfc"},
+                                                {"pg_version":"v17", "lfc_state": "without-lfc"},
+                                                {"pg_version":"v17", "lfc_state": "with-lfc"}]'
+                                           || '[{"pg_version":"v17", "lfc_state": "without-lfc"}]' }}
     secrets: inherit
 
   # Keep `benchmarks` job outside of `build-and-test-locally` workflow to make job failures non-blocking