Re: Why is subscription/t/031_column_list.pl failing so much?

On Fri, Feb 02, 2024 at 02:30:03PM -0800, Noah Misch wrote:
> On Fri, Feb 02, 2024 at 05:07:14PM -0500, Tom Lane wrote:
> > If you look at the buildfarm's failures page and filter down to
> > just subscriptionCheck failures, what you find is that all of the
> > last 6 such failures are in 031_column_list.pl:
> >
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tamandua&dt=2024-02-02%2019%3A33%3A16
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=calliphoridae&dt=2024-02-02%2011%3A21%3A44
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=flaviventris&dt=2024-02-01%2020%3A34%3A29
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=flaviventris&dt=2024-02-01%2016%3A57%3A14
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=kestrel&dt=2024-01-31%2022%3A18%3A24
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=calliphoridae&dt=2024-01-30%2011%3A29%3A23
> >
> > There are some further back too:
> >
> > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=mylodon&dt=2023-11-17%2018%3A28%3A24
> >
> > but this definitely got way more common in the last few days.
>
> > I don't see anything that 031_column_list.pl is doing that is much
> > different from other subscription tests, so why is it the only one
> > failing? And more to the point, what's going wrong exactly?
>
> I don't know, but
> https://www.postgresql.org/message-id/flat/16d6d9cc-f97d-0b34-be65-425183ed3721%40gmail.com
> reported a replacement BgWriterDelay value reproducing it.

Correction: the recipe changes LOG_SNAPSHOT_INTERVAL_MS in addition to
BgWriterDelay.

> That hasn't reproduced it in ~10 runs on my machine, though.

After 207 successes, it did fail once for me.

> > I am suspicious that this somehow represents a failure of the
> > historical catalog decoding logic, but I don't see how that theory
> > explains this only breaking in one test script.