Date: Thu, 6 Mar 2025 10:42:40 +0000
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Monitoring gaps in XLogWalRcvWrite() for the WAL receiver
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Hi,

On Thu, Mar 06, 2025 at 10:12:37AM +0900, Michael Paquier wrote:
> On Wed, Mar 05, 2025 at 08:04:44AM +0000, Bertrand Drouvot wrote:
> > On Wed, Mar 05, 2025 at 12:35:26PM +0900, Michael Paquier wrote:
> >> Perhaps there's a point in backpatching a portion of what's in the
> >> attached patch (the wait event?), but I am not planning to bother much
> >> with the stable branches based on the lack of complaints.
> > 
> > We're not emitting some statistics, so I think that it's hard for users to
> > complain about something they don't/can't see.
> 
> Hmm, not exactly actually.  I've missed that ff99918c625a mentions
> that WAL receiver was discarded on purpose, but this was still when
> pgstats was not in shared memory and still file-based.  We scale much
> better now.  It is not that difficult to make XLogWrite() hot enough
> that it would trigger a lot of calls of pgstat_count_io_op_time() per
> ms, either, like the WAL receiver, so as long as the timings are
> behind track_wal_io_timing we're fine.
> 
> Let's do this at the end, without a backpatch.  At least we'll be anle
> to get better IO metrics for replication setups.

Good catch about the comment in ff99918c625a, so yeah I think it makes sense
to not backpatch then.

Regards,

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