Hi, On 2022-04-16 13:11:59 -0400, Tom Lane wrote: > My pet dinosaur prairiedog just failed in the contrib/test_decoding > tests [1]: > > diff -U3 > /Users/buildfarm/bf-data/HEAD/pgsql.build/contrib/test_decoding/expected/stream.out > > /Users/buildfarm/bf-data/HEAD/pgsql.build/contrib/test_decoding/results/stream.out > --- > /Users/buildfarm/bf-data/HEAD/pgsql.build/contrib/test_decoding/expected/stream.out > 2022-04-15 07:59:17.000000000 -0400 > +++ > /Users/buildfarm/bf-data/HEAD/pgsql.build/contrib/test_decoding/results/stream.out > 2022-04-15 09:06:36.000000000 -0400 > @@ -77,10 +77,12 @@ > streaming change for transaction > streaming change for transaction > streaming change for transaction > + closing a streamed block for transaction > + opening a streamed block for transaction > streaming change for transaction > closing a streamed block for transaction > committing streamed transaction > -(13 rows) > +(15 rows) > > Looking at the postmaster log, it's obvious where this extra transaction > came from: auto-analyze ran on pg_type concurrently with the test step > just before this one. That could only happen if the tests ran long enough > for autovacuum_naptime to elapse, but prairiedog is a pretty slow machine. > (And I hasten to point out that some other animals, such as those running > valgrind or CLOBBER_CACHE_ALWAYS, are even slower.) > > We've seen this sort of problem before [2], and attempted to fix it [3] > by making these tests ignore empty transactions. But of course > auto-analyze's transaction wasn't empty, so that didn't help.
I don't quite understand this bit - the logic test_decoding uses to decide if a transaction is "empty" is just whether a tuple was output. And there shouldn't be any as part of auto-analyze, because we don't decode catalog changes. I suspect there's something broken in the streaming logic (potentially just in test_decoding) around skip_empty_xacts. > I think the most expedient way to prevent this type of failure is to run > the test_decoding tests with autovacuum_naptime cranked up so far as to > make it a non-issue, like maybe a day. Since test_decoding already adds > some custom settings to postgresql.conf, this'll take just a one-line > addition to test_decoding/logical.conf. I'm a bit worried about this approach - we've IIRC had past bugs that came only to light because of autovacuum starting. I wonder if we rather should do the opposite and reduce naptime so it'll be seen on fast machines, rather than very slow ones. Greetings, Andres Freund