From: Yura Sokolov <y.sokolov@postgrespro.ru>
To: Andres Freund <andres@anarazel.de>
To: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Melanie Plageman <melanieplageman@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Andrey M. Borodin <x4mmm@yandex-team.ru>
Subject: Re: Why clearing the VM doesn't require registering vm buffer in wal record
Date: Thu, 12 Mar 2026 14:25:17 +0300
Message-ID: <b231adfe-1e80-4c30-9059-1dd7752a26a9@postgrespro.ru> (raw)
In-Reply-To: <oqcsevg35xjan2327x5kdfth6q4fgeqboxfo3v3imeyih2uiny@6sez5dzxl6nt>
References: <CAAKRu_bn+e7F4yPFBgFbnP+syJRKyNK092bjD2LKvZW7O4Svag@mail.gmail.com>
<CAEze2Wh7f1zA7xQ8tR4pfuSUj6SuuVOcN5_+PkZP-69f+u-wFQ@mail.gmail.com>
<jfdhsjwcpfk5qbhm2ieopedrmiihdboux3gerzusaeosopxxpq@vsghqvzto7wj>
<oqcsevg35xjan2327x5kdfth6q4fgeqboxfo3v3imeyih2uiny@6sez5dzxl6nt>
06.03.2026 00:01, Andres Freund пишет:
> Hi,
>
> On 2026-03-05 15:38:24 -0500, Andres Freund wrote:
>>> On Thu, 5 Mar 2026 at 21:16, Andres Freund <andres@anarazel.de> wrote:
>>>>
>>>> But it does seem like it could be a problem for incremental backup /
>>>> walsummarizer?
>>>
>>> I don't think it is, because that doesn't do calculations for non-main
>>> forks, it considers those forks always changed and includes them in
>>> full. Or at least, that was the response I got when I raised concerns
>>> about the FSM back when the incremental backup feature was being
>>> developed [0].
>>
>> There's explicit code for ignoring the FSM, but I don't see the same for the
>> VM. And that makes sense: VM changes are mostly WAL logged, just not
>> completely / generically (i.e. this complaint), whereas FSM changes are not
>> WAL logged at all.
>
> Unfortunately I can confirm that incremental backups end up with an outdated
> VM.
That is why pg_probackup still archive VM at whole in incremental (WAL
parsing) backup.
That is why WAL-G's incremental backup in WAL-parsing mode is (was?)
considered unstable.
I know the problem for couple of years. Excuse me I didn't write about.
I didn't recognize fix could be as simple as registering VM buffers.
My bad. I fill so stupid :-(
It would be great if it will be fixed in all supported versions.
--
regards
Yura Sokolov aka funny-falcon
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To: pgsql-hackers@postgresql.org
Cc: y.sokolov@postgrespro.ru, andres@anarazel.de, boekewurm+postgres@gmail.com, melanieplageman@gmail.com, pgsql-hackers@lists.postgresql.org, robertmhaas@gmail.com, hlinnaka@iki.fi, x4mmm@yandex-team.ru
Subject: Re: Why clearing the VM doesn't require registering vm buffer in wal record
In-Reply-To: <b231adfe-1e80-4c30-9059-1dd7752a26a9@postgrespro.ru>
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