Re: MultiXact\SLRU buffers configuration

From: "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>
To: Thom Brown <thom(at)linux(dot)com>
Cc: Michael Paquier <michael(at)paquier(dot)xyz>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, vignesh C <vignesh21(at)gmail(dot)com>, Andrew Borodin <amborodin86(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, Andres Freund <andres(at)anarazel(dot)de>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Gilles Darold <gilles(at)darold(dot)net>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers mailing list <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: MultiXact\SLRU buffers configuration
Date: 2024-11-05 14:11:07
Message-ID: D48EEBE4-0BD8-4503-8738-1E9E069A3970@yandex-team.ru
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> On 1 Nov 2024, at 00:25, Thom Brown <thom(at)linux(dot)com> wrote:
>
> 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()".
>

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.

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