Check for invalid down link while prefetching B-Tree leave pages for index-only scan

[knizhnik]

Problem

See #9866

Index-only scan prefetch implementation doesn't take in account that down link may be invalid

Summary of changes

Check that downlink is valid block number

Correspondent Postgres PRs:
neondatabase/postgres#534
neondatabase/postgres#535
neondatabase/postgres#536
neondatabase/postgres#537

[github-actions]

5607 tests run: 5370 passed, 1 failed, 236 skipped (full report)

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Failures on Postgres 17

• test_scrubber_physical_gc_ancestors[None]: debug-x86-64

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_scrubber_physical_gc_ancestors[debug-pg17-None]"

Test coverage report is not available

_{The comment gets automatically updated with the latest test results
c8c6902 at 2024-11-25T07:52:43.337Z :recycle:}

[hlinnaka]

Please add a test case for this

[MMeent]

I don't think I understand how a downlink can contain InvalidBlockNumber, could you refer me to code which generates that?

[MMeent]

I think you have a mistaken understanding of the issue. In the issue you've linked the calculated value for skip is sometimes negative. That's bad, because we use that to read from the prefetch_blocks array, which thus causes out-of-bounds reads in that array, which finally would be the cause for InvalidBlockNumber results from that access.

I think you'll have to fix the skip calculation instead of papering over the invalid results from that skip calculation.