Re: Recent pg_rewind test failures in buildfarm

Hi,

On Mon, Apr 21, 2025 at 10:17:40AM +0900, Michael Paquier wrote:
> On Tue, Apr 15, 2025 at 05:50:32AM +0000, Bertrand Drouvot wrote:
> > Sorry, can't look at the details right now but it might be linked to
> > 039549d70f6 which is recent enough and in this area. Will give it a look once
> > I've time.
>
> Playing catch-up with various things this week, and I have been
> looking at this one.
>
> So, we are triggering this assertion in the shutdown sequence of the
> WAL sender because there is nothing to flush based on what the
> callbacks are reporting, still pending_since could have been set by a
> previous call of pgstat_report_stat(), which could come from a
> PostgresMain() path for example, depending on the frequency of such
> calls. The important point is that we don't lose WAL sender stats at
> shutdown,

Right.

> and well, we don't lose any data for the WAL sender based on
> what this assertion tells us, just that there is some friction with
> the new I/O and backend flush calls.

I do agree.

> pg_stat_io has been added in v16, but isn't that something that could
> be reached even today down to v15? For example, imagine the case of a
> background worker that does periodic stats reports with interactions
> on existing stats. pgstats stored in shmem has been added in v15.
>
> Thoughts?

Yeah, unless that might come from fc415edf8ca but I don't think that's the case.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com