For the last few days, buildfarm member parula has been intermittently failing the partition_prune regression test, due to unexpected plan changes [1][2][3][4]. The symptoms can be reproduced exactly by inserting a "vacuum" of one or another of the partitions of table "ab", so we can presume that the underlying cause is an autovacuum run against one of those tables. But why is that happening? None of those tables receive any insertions during the test, so I don't understand why autovacuum would trigger on them.
I suppose we could attach "autovacuum=off" settings to these tables, but it doesn't seem to me that that should be necessary. These test cases are several years old and haven't given trouble before. Moreover, if that's necessary then there are a lot of other regression tests that would presumably need the same treatment. I'm also baffled why this wasn't happening before. I scraped the buildfarm logs for 3 months back and confirmed my impression that this is a new failure mode. But one of these four runs is on REL_14_STABLE, eliminating the theory that the cause is a recent HEAD-only change. Any ideas? regards, tom lane [1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=parula&dt=2024-03-19%2016%3A09%3A02 [2] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=parula&dt=2024-03-18%2011%3A13%3A02 [3] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=parula&dt=2024-03-14%2011%3A40%3A02 [4] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=parula&dt=2024-03-14%2019%3A00%3A02