Re: Add min and max execute statement time in pg_stat_statement

(2014/01/22 9:34), Simon Riggs wrote:
> AFAICS, all that has happened is that people have given their opinions
> and we've got almost the same identical patch, with a rush-rush
> comment to commit even though we've waited months. If you submit a
> patch, then you need to listen to feedback and be clear about what you
> will do next, if you don't people will learn to ignore you and nobody
> wants that.
I think it was replied that will be heavily. If we realize histogram in
pg_stat_statements, we have to implement dobuble precision arrays for storing
histogram data. And when we update histogram data in each statements, we must
update arrays with searching what response time is the smallest or biggest? It is
very big cost, assuming large memory, and too hevily when updating than we get
benefit from it. So I just add stddev for as fast as latest pg_stat_statements. I
got some agreed from some people, as you say.

> On 21 January 2014 21:19, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
>> On Tue, Jan 21, 2014 at 11:48 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> I agree with people saying that stddev is better than nothing at all,
>>> so I am inclined to commit this, in spite of the above.
>>
>> I could live with stddev. But we really ought to be investing in
>> making pg_stat_statements work well with third-party tools. I am very
>> wary of enlarging the counters structure, because it is protected by a
>> spinlock. There has been no attempt to quantify that cost, nor has
>> anyone even theorized that it is not likely to be appreciable.
>
> OK, Kondo, please demonstrate benchmarks that show we have <1% impact
> from this change. Otherwise we may need a config parameter to allow
> the calculation.
OK, testing DBT-2 now. However, error range of benchmark might be 1% higher. So I
show you detail HTML results.

Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center