| From: | "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru> |
|---|---|
| To: | Amul Sul <sulamul(at)gmail(dot)com> |
| Cc: | Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, tender wang <tndrwang(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock |
| Date: | 2023-12-14 09:01:52 |
| Message-ID: | 7A701EEA-23A4-43DB-A5BE-BE6702D4565F@yandex-team.ru |
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| Lists: | pgsql-hackers |
> On 14 Dec 2023, at 08:12, Amul Sul <sulamul(at)gmail(dot)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.
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