Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

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(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)
>>>
>>> +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
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company