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: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, tender wang <tndrwang@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-12-22T13:14:17Z
Lists: pgsql-hackers 

> On 19 Dec 2023, at 10:34, Dilip Kumar <dilipbalaut@gmail.com> wrote:

Just a side node.
It seems like commit log is kind of antipattern of data contention. Even when we build a super-optimized SLRU. Nearby **bits** are written by different CPUs.
I think that banks and locks are good thing. But also we could reorganize log so that 
status of transaction 0 is on a page 0 at bit offset 0
status of transaction 1 is on a page 1 at bit offset 0
status of transaction 2 is on a page 2 at bit offset 0
status of transaction 3 is on a page 3 at bit offset 0
status of transaction 4 is on a page 0 at bit offset 2
status of transaction 5 is on a page 1 at bit offset 2
status of transaction 6 is on a page 2 at bit offset 2
status of transaction 7 is on a page 3 at bit offset 2
etc...

And it would be even better if page for transaction statuses would be determined by backend id somehow. Or at least cache line. Can we allocate a range (sizeof(cacheline)) of xids\subxids\multixacts\whatever for each backend?

This does not matter much because
0. Patch set in current thread produces robust SLRU anyway
1. One day we are going to throw away SLRU anyway


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.