| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> |
| Cc: | Ronan Dunklau <ronan(dot)dunklau(at)aiven(dot)io>, James Coleman <jtc331(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Subject: | Re: [PATCH] Use optimized single-datum tuplesort in ExecSort |
| Date: | 2021-07-15 00:20:58 |
| Message-ID: | CAApHDvoU_-r8A-Ztp2jrdxXp8iuH08TLgAigwjyLzK+jBFs+Eg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, 15 Jul 2021 at 12:10, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> wrote:
>
> Em qua., 14 de jul. de 2021 às 20:43, David Rowley <dgrowleyml(at)gmail(dot)com> escreveu:
>>
>> On Thu, 15 Jul 2021 at 05:55, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> wrote:
>> > I repeated (3 times) the benchmark with v8 here,
>> > and the results were not good.
>>
>> Do you have any good theories on why the additional branching that's
>> done in v7b vs v8 might cause it to run faster?
>
>
> Branch Predictions works with *more* probable path,
> otherwise a penalty occurs and the cpu must revert the results.
But, in v8 there is no additional branch, so no branch to mispredict.
I don't really see how your explanation fits.
It seems much more likely to me that the results were just noisy. It
would be good to see if you can recreate them consistently.
David
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