Horton

Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock

x4mmm@yandex-team.ru

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From: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-11-06T11:14:32Z
Lists: pgsql-hackers 

> On 6 Nov 2023, at 14:31, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> 
> dynahash is notoriously slow, which is why we have simplehash.h since
> commit b30d3ea824c5.  Maybe we could use that instead.

Dynahash has lock partitioning. Simplehash has not, AFAIK.
The thing is we do not really need a hash function - pageno is already a best hash function itself. And we do not need to cope with collisions much - we can evict a collided buffer.

Given this we do not need a hashtable at all. That’s exact reasoning how banks emerged, I started implementing dynahsh patch in April 2021 and found out that “banks” approach is cleaner. However the term “bank” is not common in software, it’s taken from hardware cache.


Best regards, Andrey Borodin.

Commits

  1. Fix zeroing of pg_serial page without SLRU bank lock

  2. Fix misspelled assertions

  3. GUC table: Add description to computed variables

  4. Improve performance of subsystems on top of SLRU

  5. Rename SLRU elements in view pg_stat_slru

  6. Use atomic access for SlruShared->latest_page_number

  7. Split use of SerialSLRULock, creating SerialControlLock

  8. Index SLRUs by 64-bit integers rather than by 32-bit integers

  9. Add a macro templatized hashtable.