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Subject: Re: MultiXact\SLRU buffers configuration
From: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
In-Reply-To: <CAA-aLv7-fs32r7v8znJ=uPPtQNqZ9_sH2REn=cu1pyEQ=tuEhw@mail.gmail.com>
Date: Tue, 5 Nov 2024 19:11:07 +0500
Cc: Michael Paquier <michael@paquier.xyz>,
 Alvaro Herrera <alvherre@alvh.no-ip.org>,
 vignesh C <vignesh21@gmail.com>,
 Andrew Borodin <amborodin86@gmail.com>,
 Yura Sokolov <y.sokolov@postgrespro.ru>,
 Andres Freund <andres@anarazel.de>,
 Thomas Munro <thomas.munro@gmail.com>,
 Gilles Darold <gilles@darold.net>,
 Alexander Korotkov <aekorotkov@gmail.com>,
 Daniel Gustafsson <daniel@yesql.se>,
 Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
 pgsql-hackers mailing list <pgsql-hackers@postgresql.org>
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To: Thom Brown <thom@linux.com>
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> On 1 Nov 2024, at 00:25, Thom Brown <thom@linux.com> wrote:
>=20
> Unfortunately I didn't gather much information when it was occuring, =
and prioritised getting rid of the process blocking replay. I just =
attached gdb to it, got a backtrace and then "print =
ProcessInterrupts()".
>=20

Currently I do not see how this wait can result in a deadlock.
But I did observe standby in a pathological sequential scan encountering =
recent multixact again and again (new each time).
I hope this situation will be alleviated by recent cahnges - now there =
is not a millisecond wait, but hopefully smaller amount of time.

In v17 we also added injection point test which reproduces reading very =
recent multixact. If there is a deadlock I hope buildfarm will show it =
to us.


Best regards, Andrey Borodin.=