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Date: Fri, 20 Jan 2023 12:13:09 +0100
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Subject: Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?
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To: David Geier <geidav.pg@gmail.com>, Pavel Stehule <pavel.stehule@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>, Lukas Fittl <lukas@fittl.com>,
 Michael Paquier <michael@paquier.xyz>, Ibrar Ahmed <ibrar.ahmad@gmail.com>,
 Maciek Sakrejda <m.sakrejda@gmail.com>, Andres Freund <andres@anarazel.de>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
In-Reply-To: <24aa958f-0463-03d4-ce54-20b277c954c6@gmail.com>
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On 1/20/23 07:43, David Geier wrote:
> On 1/18/23 13:52, David Geier wrote:
>> On 1/16/23 21:39, Pavel Stehule wrote:
>>>
>>> po 16. 1. 2023 v 21:34 odesílatel Tomas Vondra
>>> <tomas.vondra@enterprisedb.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)
>>>
>>> +1
>>
>> 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.
> Thinking about this a little more made me realize that this will cause
> different pg_regress output depending on the platform. So if we go this
> route we would at least need an option for EXPLAIN ANALYZE to disable
> it. Or rather have it disabled by default and allow for enabling it.
> Thoughts?
> 

What about only showing it for VERBOSE mode? I don't think there are
very many tests doing EXPLAIN (ANALYZE, VERBOSE) - a quick grep found
one such place in partition_prune.sql.

regards

-- 
Tomas Vondra
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