Re: auto_explain sample rate

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От Magnus Hagander
Тема Re: auto_explain sample rate
Дата
Msg-id CABUevEwh0zqLEwFwZo5M9dLjcfvq2yP4cSc0nXeJLqLs3DeiKA@mail.gmail.com
обсуждение исходный текст
Ответ на Re: auto_explain sample rate  (Petr Jelinek <petr@2ndquadrant.com>)
Ответы Re: auto_explain sample rate  (Julien Rouhaud <julien.rouhaud@dalibo.com>)
Re: auto_explain sample rate  (Petr Jelinek <petr@2ndquadrant.com>)
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Дерево обсуждения


On Thu, Mar 10, 2016 at 10:07 PM, Petr Jelinek <petr@2ndquadrant.com> wrote:
On 10/03/16 20:59, Julien Rouhaud wrote:
On 10/03/2016 04:37, Petr Jelinek wrote:
On 17/02/16 01:17, Julien Rouhaud wrote:

Agreed, it's too obscure. Attached v4 fixes as you said.


Seems to be simple enough patch and works. However I would like
documentation to say that the range is 0 to 1 and represents fraction of
the queries sampled, because right now both the GUC description and the
documentation say it's in percent but that's not really true as percent
is 0 to 100.


Agreed. v5 attached fixes that.


 Great, I will test it once more (just because when I don't bugs suddenly appear out of nowhere) and mark it ready for committer.


Coming back to the previous discussions about random() - AFAICT this patch will introduce the random() call always (in explain_ExecutorStart):

+ if (auto_explain_log_min_duration >= 0 && nesting_level == 0)
+ current_query_sampled = (random() < auto_explain_sample_ratio *
+ MAX_RANDOM_VALUE);


Not sure what the overhead is, but wouldn't it be better to include a check for current_query_sampled>0 in the  if part of that statement? Regardless of performance, that feels cleaner to me. Or am I missing something?


--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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