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: Amul Sul <sulamul@gmail.com>
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: 2023-12-14T09:01:52Z
Lists: pgsql-hackers 

> On 14 Dec 2023, at 08:12, Amul Sul <sulamul@gmail.com> wrote:
> 
> 
> + int bankno = pageno & ctl->bank_mask;
> 
> I am a bit uncomfortable seeing it as a mask, why can't it be simply a number
> of banks (num_banks) and get the bank number through modulus op (pageno %
> num_banks) instead of bitwise & operation (pageno & ctl->bank_mask) which is a
> bit difficult to read compared to modulus op which is quite simple,
> straightforward and much common practice in hashing.
> 
> Are there any advantages of using &  over % ?

The instruction AND is ~20 times faster than IDIV [0]. This is relatively hot function, worth sacrificing some readability to save ~ten nanoseconds on each check of a status of a transaction.


[0] https://www.agner.org/optimize/instruction_tables.pdf

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.