Horton

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

Amul Sul <sulamul@gmail.com>

View thread View on postgr.es
From: Amul Sul <sulamul@gmail.com>
To: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Dilip Kumar <dilipbalaut@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-11-08T05:09:34Z
Lists: pgsql-hackers 
On Mon, Nov 6, 2023 at 4:44 PM Andrey M. Borodin <x4mmm@yandex-team.ru>
wrote:

>
>
> > 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.
>

I agree that we don't need the hash function to generate hash value out of
pageno which itself is sufficient, but I don't understand how we can get
rid of
the hash table itself -- how we would map the pageno and the slot number?
That mapping is not needed at all?

Regards,
Amul

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.