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

On Mon, Nov 6, 2023 at 4:44 PM Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru>
wrote:

>
>
> > On 6 Nov 2023, at 14:31, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)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