On Fri, Jan 12, 2024 at 01:46:08PM +0000, Bertrand Drouvot wrote: > 1) Michael's proposal up-thread (means tweak the test with a retry logic, > retrying > things if such a standby snapshot is found). > > 2) Don't report a test error for active slots in case its catalog_xmin > advanced. > > I'd vote for 2) as: > > - this is a corner case and the vast majority of the animals don't report any > issues (means the active slot conflict detection is already well covered). > > - even on the same animal it should be pretty rare to not have an active slot > conflict detection not covered at all (and the "failing" one would be probably > moving over time). > > - It may be possible that 1) ends up failing (as we'd need to put a limit on > the > retry logic anyhow). > > What do you think? > > And BTW, looking closely at wait_until_vacuum_can_remove(), I'm not sure it's > fully correct, so I'll give it another look.
The WAL records related to standby snapshots are playing a lot with the randomness of the failures we are seeing. Alexander has mentioned offlist something else: using SIGSTOP on the bgwriter to avoid these records and make the test more stable. That would not be workable for Windows, but I could live with that knowing that logical decoding for standbys has no platform-speficic tweak for the code paths we're testing here, and that would put as limitation to skip the test for $windows_os. While thinking about that, a second idea came into my mind: a superuser-settable developer GUC to disable such WAL records to be generated within certain areas of the test. This requires a small implementation, but nothing really huge, while being portable everywhere. And it is not the first time I've been annoyed with these records when wanting a predictible set of WAL records for some test case. Another possibility would be to move these records elsewhere, outside of the bgwriter, but we need such records at a good frequency for the availability of read-only standbys. And surely we'd want an on/off switch anyway to get a full control for test sequences. -- Michael
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