Re: Introduce wait_for_subscription_sync for TAP tests

On Mon, Sep 12, 2022 at 10:42 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> On Sat, Sep 10, 2022 at 10:00 AM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> > On Sat, Sep 10, 2022 at 9:45 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > > Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> writes:
> > > > It's likely that the commit f6c5edb8abcac04eb3eac6da356e59d399b2bcef
> > > > is relevant.
> > >
> > > Noting that the errors have only appeared in the past couple of
> > > days, I'm now suspicious of adb466150b44d1eaf43a2d22f58ff4c545a0ed3f
> > > (Fix recovery_prefetch with low maintenance_io_concurrency).
> >
> > Yeah, I also just spotted the coincidence of those failures while
> > monitoring the build farm. I'll look into this later today. My
> > initial suspicion is that there was pre-existing code here that was
> > (incorrectly?) relying on the lack of error reporting in that case.
> > But maybe I misunderstood and it was incorrect to report the error for
> > some reason that was not robustly covered with tests.
>
> After I wrote that I saw Sawada-san's message and waited for more
> information, and I see there was now a commit. I noticed that
> peripatus was already logging the 'missing contrecord' error even when
> it didn't fail the test, and still does. I'm still looking into that
> (ie whether I need to take that new report_invalid_record() call out
> and replace it with errormsg_deferred = true so that XLogReadRecord()
> returns NULL with no error message in this case).

I will go ahead and remove this new error message added by adb46615.
The message was correlated with the problem on peripatus fixed by
88f48831, but not the cause of it -- but it's also not terribly
helpful and might be confusing. It might be reported: (1) in
pg_waldump when you hit the end of the segment with a missing
contrecord after the end, arguably rightfully, but then perhaps
someone might complain that they expect an error from pg_waldump only
on the final live segment at the end of the WAL, and (2) in a
walsender that is asked to shut down while between reads of pages with
a spanning contrecord, reported by logical_read_xlog_page() with a
messageless error (presumably peripatus's case?), (3) in crash
recovery with wal_recycle off (whereas normally you'd expect to see
the page_addr message from a recycled file), maybe more legitimately
than the above. The problem I needed to solve can be solved without
the message just by setting that flag as mentioned above, so I'll do
that to remove the new noise.