Re: Why clearing the VM doesn't require registering vm buffer in wal record

12.03.2026 14:25, Yura Sokolov пишет:
> 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(at)anarazel(dot)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 Unfortunately I can confirm that incremental backups end up with an outdated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 :-(
Should LSN properly set as well on vm page? To maximum of concurrent
updates, of course.

--
regards
Yura Sokolov aka funny-falcon