| From: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com> |
|---|---|
| To: | Hannu Krosing <hannuk(at)google(dot)com> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [PoC] Improve dead tuple storage for lazy vacuum |
| Date: | 2022-06-28 04:17:42 |
| Message-ID: | CAFBsxsH6oux2Q0bmdyAHZbqfcNfAmAW0yvGzDzNH1H8RR2Qx-g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jun 27, 2022 at 10:23 PM Hannu Krosing <hannuk(at)google(dot)com> wrote:
>
> > Another thought: for non-x86 platforms, the SIMD nodes degenerate to
> > "simple loop", and looping over up to 32 elements is not great
> > (although possibly okay). We could do binary search, but that has bad
> > branch prediction.
>
> I am not sure that for relevant non-x86 platforms SIMD / vector
> instructions would not be used (though it would be a good idea to
> verify)
By that logic, we can also dispense with intrinsics on x86 because the
compiler will autovectorize there too (if I understand your claim
correctly). I'm not quite convinced of that in this case.
> I would definitely test before assuming binary search is better.
I wasn't very clear in my language, but I did reject binary search as
having bad branch prediction.
--
John Naylor
EDB: http://www.enterprisedb.com
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