Re: 001_rep_changes.pl fails due to publisher stuck on shutdown

On Thu, 6 Jun 2024 at 11:49, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Thu, 6 Jun 2024 12:49:45 +1000, Peter Smith <smithpb2250(at)gmail(dot)com> wrote in
> > Hi, I have reproduced this multiple times now.
> >
> > I confirmed the initial post/steps from Alexander. i.e. The test
> > script provided [1] gets itself into a state where function
> > ReadPageInternal (called by XLogDecodeNextRecord and commented "Wait
> > for the next page to become available") constantly returns
> > XLREAD_FAIL. Ultimately the test times out because WalSndLoop() loops
> > forever, since it never calls WalSndDone() to exit the walsender
> > process.
>
> Thanks for the repro; I believe I understand what's happening here.
>
> During server shutdown, the latter half of the last continuation
> record may fail to be flushed. This is similar to what is described in
> the commit message of commit ff9f111bce. While shutting down,
> WalSndLoop() waits for XLogSendLogical() to consume WAL up to
> flushPtr, but in this case, the last record cannot complete without
> the continuation part starting from flushPtr, which is
> missing. However, in such cases, xlogreader.missingContrecPtr is set
> to the beginning of the missing part, but something similar to
>
> So, I believe the attached small patch fixes the behavior. I haven't
> come up with a good test script for this issue. Something like
> 026_overwrite_contrecord.pl might work, but this situation seems a bit
> more complex than what it handles.
>
> Versions back to 10 should suffer from the same issue and the same
> patch will be applicable without significant changes.

I tested the changes for PG 12 to master as we do not support prior versions.
The patch applied successfully for master and PG 16. I ran the test
provided in [1] multiple times and it ran successfully each time.
The patch did not apply on PG 15. I did a similar change for PG 15 and
created a patch. I ran the test multiple times and it was successful
every time.
The patch did not apply on PG 14 to PG 12. I did a similar change in
each branch. But the tests did not pass in each branch.

I have attached a patch which applies successfully on the PG 15 branch.

[1]: https://www.postgresql.org/message-id/f15d665f-4cd1-4894-037c-afdbe369287e@gmail.com

Thanks and Regards,
Shlok Kyal