Fix race condition in XLogWaitForReplayOf() #7804
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I spotted this while debugging #7791, but I don't think this has been causing any noticeable problems in practice. |
3078 tests run: 2952 passed, 0 failed, 126 skipped (full report)Flaky tests (2)Postgres 15
Postgres 14
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* collected from Rust tests only The comment gets automatically updated with the latest test results
8dc1c48 at 2024-05-19T18:55:45.098Z :recycle: |
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knizhnik
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ConditionVariablePrepareToSleep has this comment on it: > * Caution: "before entering the loop" means you *must* test the exit > * condition between calling ConditionVariablePrepareToSleep and calling > * ConditionVariableSleep. If that is inconvenient, omit calling > * ConditionVariablePrepareToSleep. We were not obeying that: we did not test the exit condition correctly between the ConditionVariablePrepareToSleep and ConditionVariableSleep calls, because the test that we had in between them only checked the local 'replayRecPtr' variable, without updating it from shared memory. That wasn't too serious, because the loop includes a 10 second timeout, and would retry and succeed if the original update was missed. Still, better fix it. To fix, just remove the ConditionVariablePrepareToSleep() call. As the comment says, that's also correct, and even more efficient if we assume that sleeping is rare.
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It seems correct to me. Because I'm also removing the call to
That was a mistake, there were not supposed to be any bufmgr changs for pg16 either. Thanks! |
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ConditionVariablePrepareToSleep has this comment on it:
We were not obeying that: we did not test the exit condition correctly between the ConditionVariablePrepareToSleep and ConditionVariableSleep calls, because the test that we had in between them only checked the local 'replayRecPtr' variable, without updating it from shared memory.
That wasn't too serious, because the loop includes a 10 second timeout, and would retry and succeed if the original update was missed. Still, better fix it.
To fix, just remove the ConditionVariablePrepareToSleep() call. As the comment says, that's also correct, and even more efficient if we assume that sleeping is rare.