Date: Mon, 31 Aug 2026 11:38:40 +0000
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Zsolt Parragi <zsolt.parragi@percona.com>
Cc: Daniel Gustafsson <daniel@yesql.se>, pgsql-hackers@lists.postgresql.org
Subject: Re: Offline data checksum changes can cause incorrect checksum state
 on standbys
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Hi,

On Mon, Aug 31, 2026 at 11:55:01AM +0100, Zsolt Parragi wrote:
> > Yeah, I see your point that the underlying issue is the non WAL logged change.
> > My concern was not about a pg_control change in itself, but that addressing this
> > case might require further changes to the current pg_control design, which adds
> > risk this close to RC1.
> 
> I don't think we can get this completely right without both wal and
> pg_control changes (and possibly some extra connection-time
> communication between the standby and primary to provide early
> reporting instead of delayed in the most common cases)
> If we want to move toward the error direction in pg20 (which we
> should) we will have to log that an offline change happened.
> 
> I attached v6 which for now documents the current behavior as-is, and
> other than that I reorganized the test files.

Thanks! I did not look in details but it looks like that pg_upgrade --check against
a running source cluster with checksums enabled will still fail (finding === 2 in
[0], tested with the test shared in [1]).

[0]: https://postgr.es/m/apUL3N4IE934qJ08%40bdtpg
[1]: https://postgr.es/m/apU4/hmRv/4gv20W%40bdtpg

Regards,

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