Date: Wed, 15 Jan 2025 16:00:12 +0000
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Nazir Bilal Yavuz <byavuz81@gmail.com>
Cc: Michael Paquier <michael@paquier.xyz>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	pgsql-hackers@lists.postgresql.org,
	Andres Freund <andres@anarazel.de>
Subject: Re: per backend I/O statistics
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Hi,

On Wed, Jan 15, 2025 at 05:20:57PM +0300, Nazir Bilal Yavuz wrote:
> While doing the initdb, we are restoring stats with the
> pgstat_restore_stats() and we do not expect any pending stats. The
> problem goes like that:
> 
> I was a bit surprised that Bertrand did not encounter the same problem
> while working on the 'per backend WAL statistics' patch. Then I found
> the reason, it is because this problem happens only for WAL read and
> WAL init IOs which are starting to be tracked in my patch. By saying
> that, I could not decide which thread to write about this problem,
> migrating WAL stats thread or this thread. Since this thread is active
> and other stats may cause the same problem, I decided to write here.
> Please warn me if you think I need to write this to the migrating WAL
> stats thread.

Thanks for the report! As it looks like that you hit the issue for "WAL read and
WAL init IOs which are starting to be tracked in my patch", then I think it would
make more sense to mention the issue in the "migrating WAL stats thread" so that
one could try to reproduce it (with a patch producing the issue at hands).

So it seems to me that the "migrating WAL stats thread" is a better place to
discuss about it.

Regards,

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