Re: BF member drongo doesn't like 035_standby_logical_decoding.pl

I realized just now that drongo has been intermittently failing like this:

147/256 postgresql:recovery / recovery/035_standby_logical_decoding               ERROR          2116.16s   (exit status 255 or signal 127 SIGinvalid)
------------------------------------- 8< -------------------------------------
stderr:
#   Failed test 'activeslot slot invalidation is logged with vacuum on pg_class'
#   at C:/prog/bf/root/REL_16_STABLE/pgsql/src/test/recovery/t/035_standby_logical_decoding.pl line 229.
# poll_query_until timed out executing this query:
# select (confl_active_logicalslot = 1) from pg_stat_database_conflicts where datname = 'testdb'
# expecting this output:
# t
# last actual query output:
# f
# with stderr:
#   Failed test 'confl_active_logicalslot updated'
#   at C:/prog/bf/root/REL_16_STABLE/pgsql/src/test/recovery/t/035_standby_logical_decoding.pl line 235.
# Tests were run but no plan was declared and done_testing() was not seen.
# Looks like your test exited with 255 just after 24.

This has been happening for some time, in all three branches where
that test script exists.  The oldest failure that looks like that in
the v16 branch is

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=drongo&dt=2024-09-06%2004%3A19%3A35

However, there are older failures showing a timeout of
035_standby_logical_decoding.pl that don't provide any detail, but
might well be the same thing.  The oldest one of those is from
2024-05-01, which is still considerably later than the test script
itself (added on 2023-04-08).  So it would seem that this is something
we broke during 2024, rather than an aboriginal problem in this test.

A search of the buildfarm logs did not turn up similar failures
on any other animals.

I have no idea how to proceed on narrowing down the cause...

Please take a look at the list of such failures since 2024-06-01 I
collected here:
https://wiki.postgresql.org/wiki/Known_Buildfarm_Test_Failures#035_standby_logical_decoding_standby.pl_fails_due_to_missing_activeslot_invalidation

There is also a reference to a discussion of the failure there:
https://www.postgresql.org/message-id/657815a2-5a89-fcc1-1c9d-d77a6986bc26@gmail.com
(In short, I observed that that test suffers from bgwriter's activity.)

Best regards,
Alexander Lakhin
Neon (https://neon.tech)