Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

From: David Geier <geidav(dot)pg(at)gmail(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
Cc: vignesh C <vignesh21(at)gmail(dot)com>, Lukas Fittl <lukas(at)fittl(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com>, Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?
Date: 2023-01-18 12:52:05
Message-ID: b929cab3-c07f-6d89-5a5f-35d5e5e9ba8a@gmail.com
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On 1/16/23 21:39, Pavel Stehule wrote:
>
> po 16. 1. 2023 v 21:34 odesílatel Tomas Vondra
> <tomas(dot)vondra(at)enterprisedb(dot)com> napsal:
>
> Hi,
>
> there's minor bitrot in the Mkvcbuild.pm change, making cfbot unhappy.
>
> As for the patch, I don't have much comments. I'm wondering if it'd be
> useful to indicate which timing source was actually used for EXPLAIN
> ANALYZE, say something like:
>
>  Planning time: 0.197 ms
>  Execution time: 0.225 ms
>  Timing source: clock_gettime (or tsc)
>
> There has been a proposal to expose this as a GUC (or perhaps as
> explain
> option), to allow users to pick what timing source to use. I
> wouldn't go
> that far - AFAICS is this is meant to be universally better when
> available. But knowing which source was used seems useful.
>
>
> +1

Thanks for looking at the patch.

I'll fix the merge conflict.

I like the idea of exposing the timing source in the EXPLAIN ANALYZE output.
It's a good tradeoff between inspectability and effort, given that RDTSC
should always be better to use.
If there are no objections I go this way.

--
David Geier
(ServiceNow)

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