Re: MultiXact\SLRU buffers configuration

From: Gilles Darold <gilles(at)darold(dot)net>
To: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Cc: Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: MultiXact\SLRU buffers configuration
Date: 2020-12-10 14:45:56
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Le 08/12/2020 à 18:52, Andrey Borodin a écrit :
> Hi Gilles!
> Many thanks for your message!
>> 8 дек. 2020 г., в 21:05, Gilles Darold <gilles(at)darold(dot)net> написал(а):
>> I know that this report is not really helpful
> Quite contrary - this benchmarks prove that controllable reproduction exists. I've rebased patches for PG11. Can you please benchmark them (without extending SLRU)?
> Best regards, Andrey Borodin.

Running tests yesterday with the patches has reported log of failures
with error on INSERT and UPDATE statements:

ERROR:  lock MultiXactOffsetControlLock is not held

After a patch review this morning I think I have found what's going
wrong. In patch
v6-0001-Use-shared-lock-in-GetMultiXactIdMembers-for-offs.patch I think
there is a missing reinitialisation of the lockmode variable to LW_NONE
inside the retry loop after the call to LWLockRelease() in
I've attached a new version of the patch for master that include the fix
I'm using now with PG11 and with which everything works very well now.

I'm running more tests to see the impact on the performances to play
with multixact_offsets_slru_buffers, multixact_members_slru_buffers and
multixact_local_cache_entries. I will reports the results later today.

Gilles Darold

Attachment Content-Type Size
v7-0001-Use-shared-lock-in-GetMultiXactIdMembers-for-offs.patch text/x-patch 11.6 KB

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