Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, tender wang <tndrwang@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-01-02T14:23:27Z
Lists: pgsql-hackers 
On Fri, Dec 22, 2023 at 8:14 AM Andrey M. Borodin <x4mmm@yandex-team.ru> 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...

This is an interesting idea. A variant would be to stripe across
cachelines within the same page rather than across pages. If we do
stripe across pages as proposed here, we'd probably want to rethink
the way the SLRU is extended -- page at a time wouldn't really make
sense, but preallocating an entire file might.

> 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?

I don't understand how this could work. We need to be able to look up
transaction status by XID, not backend ID.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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.