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

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От Amul Sul
Тема Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock
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Msg-id CAAJ_b96MDOxVk=DTFNq-TX448gYD-pz8e9LvaXYX5ZybF-mBQQ@mail.gmail.com
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Ответ на Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock  ("Andrey M. Borodin" <x4mmm@yandex-team.ru>)
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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

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