RE: Planning counters in pg_stat_statements (using pgss_store)

On Wed, Nov 20, 2019 at 4:55 PM, Julien Rouhaud wrote:
> On Wed, Nov 20, 2019 at 2:06 AM imai(dot)yoshikazu(at)fujitsu(dot)com <imai(dot)yoshikazu(at)fujitsu(dot)com> wrote:
> >
> > On Tue, Nov 19, 2019 at 2:27 PM, Julien Rouhaud wrote:
> > > On Fri, Nov 15, 2019 at 2:00 AM imai(dot)yoshikazu(at)fujitsu(dot)com <imai(dot)yoshikazu(at)fujitsu(dot)com> wrote:
> > > >
> > > > Actually I also don't have strong opinion but I thought someone
> > > > would complain about renaming of those columns and
> > > also some tools like monitoring which use those columns will not
> > > work. If we use {total, min, max, mean, stddev}_time, someone might
> > > mistakenly understand {total, min, max, mean, stddev}_time mean {total, min, max, mean, stddev} of planning and
> execution.
> > > > If I need to choose {total, min, max, mean, stddev}_time or
> > > > {total, min, max, mean, stddev}_exec_time, I choose former
> > > one because choosing best name is not worth destructing the existing scripts or tools.
> > >
> > > We could definitely keep (plan|exec)_time for the SRF, and have the
> > > {total, min, max, mean, stddev}_time created by the view to be a sum
> > > of planning + execution for each counter
> >
> > I might misunderstand but if we define {total, min, max, mean,
> > stddev}_time is just a sum of planning + execution for each counter
> > like "select total_plan_time + total_exec_time as total_time from
> > pg_stat_statements", I wonder we can calculate stddev_time correctly.
> > If we prepare variables in the codes to calculate those values, yes,
> > we can correctly calculate those values even for the total_stddev.
>
> Yes you're right, this can't possibly work for most of the counters.
> And also, since there's no guarantee that each execution will follow a planning, providing such global counters for
> min/max/mean and stddev wouldn't make much sense.

Ah, I see. Planning counts and execution counts differ.
It might be difficult to redefine the meaning of {min, max, mean, stddev}_time precisely, and even if we can redefine it correctly, it would not be intuitive.

--
Yoshikazu Imai