From: Chao Li <li.evan.chao@gmail.com>
To: Yura Sokolov <y.sokolov@postgrespro.ru>
Cc: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Andres Freund <andres@anarazel.de>
Cc: Sami Imseih <samimseih@gmail.com>
Subject: Re: Fix bug in multixact Oldest*MXactId initialization and access
Date: Thu, 26 Feb 2026 10:21:10 +0800
Message-ID: <C991344D-F38A-4EEC-903A-72B52FF887FA@gmail.com> (raw)
In-Reply-To: <c3eaaac1-d244-4e4d-b5d7-06c284108eac@postgrespro.ru>
References: <7acc94b0-ea82-4657-b1b0-77842cb7a60c@postgrespro.ru>
<93F0BD0A-0B8B-4592-9D4B-53F405A86F6A@gmail.com>
<c3eaaac1-d244-4e4d-b5d7-06c284108eac@postgrespro.ru>
> On Feb 25, 2026, at 23:16, Yura Sokolov <y.sokolov@postgrespro.ru> wrote:
>
> Good day.
>
> Chao Li and Sami Imseih, thank you for looking at.
>
> After thinking a bit, I've decided to make sizes of arrays precise:
> - OldestMemberMXactId's size remains MaxBackends + max_prepared_xacts.
> Instead of changing its size, procno is now adjusted to not include
> auxiliary procs.
> - OldestVisibleMXactId contains only MaxBackends elemenents now.
> It is used only for real backends and not prepared transactions.
>
> All accesses are validated with asserts certainly.
>
> I believe, index transformation in access of OldestMemberMXactId will not
> cost much since all this operations are quite rare.
> In the loops arrays are accessed directly since limiting loop index is enough.
>
> --
> regards
> Yura Sokolov aka funny-falcon<v3-0001-Fix-multixacts-OldestMemberMXactId-and-OldestVisi.patch>
Actually, while I reviewing v1, I was thinking over the same way as v3, as the NUM_AUXILIARY_PROCS portions in OldestMemberMXactId and OldestVisibleMXactId arrays are not used at all. I didn’t raise the idea because that given these code are in hot paths, I wasn't sure if the complexity was worth the shared memory optimization. It’s a classic trade-off, and I’m curious to see which direction the senior committers prefer.
However, I agree that the new helper function names in v3 are a significant improvement over v1.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
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To: pgsql-hackers@postgresql.org
Cc: li.evan.chao@gmail.com, y.sokolov@postgrespro.ru, pgsql-hackers@lists.postgresql.org, hlinnaka@iki.fi, andres@anarazel.de, samimseih@gmail.com
Subject: Re: Fix bug in multixact Oldest*MXactId initialization and access
In-Reply-To: <C991344D-F38A-4EEC-903A-72B52FF887FA@gmail.com>
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