Horton

Re: MultiXact\SLRU buffers configuration

x4mmm@yandex-team.ru

View thread View on postgr.es
From: Andrey Borodin <x4mmm@yandex-team.ru>
To: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: Gilles Darold <gilles@darold.net>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Alexander Korotkov <aekorotkov@gmail.com>, Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, Daniel Gustafsson <daniel@yesql.se>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2021-12-26T10:09:59Z
Lists: pgsql-hackers

Attachments


>> 8 апр. 2021 г., в 15:22, Thomas Munro <thomas.munro@gmail.com> написал(а):
>>
> I have one more idea inspired by CPU caches.
> Let's make SLRU n-associative, where n ~ 8.
> We can divide buffers into "banks", number of banks must be power of 2.
> All banks are of equal size. We choose bank size to approximately satisfy user's configured buffer size.
> Each page can live only within one bank. We use same search and eviction algorithms as we used in SLRU, but we only need to search\evict over 8 elements.
> All SLRU data of a single bank will be colocated within at most 2 cache line.
> 
> I did not come up with idea how to avoid multiplication of bank_number * bank_size in case when user configured 31337 buffers (any number that is radically not a power of 2).

We can avoid this multiplication by using gapped memory under SLRU page_statuses, but from my POV here complexity does not worth possible performance gain.

PFA rebase of the patchset. Also I've added a patch to combine page_number, page_status, and page_dirty together to touch less cachelines.

Best regards, Andrey Borodin.

Commits

  1. Rework new SLRU test with injection points

  2. injection_point: Add injection_points.stats

  3. injection_points: Add initialization of shmem state when loading module

  4. Add injection-point test for new multixact CV usage

  5. Use conditional variable to wait for next MultiXact offset

  6. Improve performance of subsystems on top of SLRU

  7. Adjust VACUUM hastup LP_REDIRECT comments.

  8. Test replay of regression tests, attempt II.