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Subject: Re: Bug in MultiXact replay compat logic for older minor version
 after crash-recovery
From: Andrey Borodin <x4mmm@yandex-team.ru>
In-Reply-To: <452355ef-7c20-4d96-88a2-8fbb49737dc9@iki.fi>
Date: Fri, 20 Mar 2026 16:39:32 +0300
Cc: =?utf-8?B?IuauteWdpOS7gSjliLvpn6cpIg==?= <duankunren.dkr@alibaba-inc.com>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
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Message-Id: <BD37E553-A017-4D2C-8203-702378BF5882@yandex-team.ru>
References: 
 <c4ef1737-8cba-458e-b6fd-4e2d6011e985.duankunren.dkr@alibaba-inc.com>
 <18a40051-abc2-4fc2-8dcc-4dc39aa3e79e@iki.fi>
 <F513DFBB-DCFE-4B99-B01E-DDB04414857C@yandex-team.ru>
 <452355ef-7c20-4d96-88a2-8fbb49737dc9@iki.fi>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Archived-At: 
 <https://www.postgresql.org/message-id/BD37E553-A017-4D2C-8203-702378BF5882%40yandex-team.ru>
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> On 20 Mar 2026, at 16:19, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>=20
> Hmm, after startup, before we have zeroed any pages, it still works =
though. So I think my patch works, but it means that tracking the latest =
page we have zeroed is not merely an optimization to avoid excessive =
SimpleLruDoesPhysicalPageExist() calls, it's needed for correctness. =
Need to adjust the comments for that.

If we are sure buffers have no this page we can detect it via FS.
Otherwise... nothing bad can happen, actually. We might get false =
positive and zero the page once more.

If we got init_needed=3D=3Dfalse, maybe cache it for this page and set =
last_initialized_offsets_page =3D pageno?
Or, perhaps, XLOG_MULTIXACT_ZERO_OFF_PAGE will do it for us anyway, but =
a bit later.

Best regards, Andrey Borodin.=