Re: Add min and max execute statement time in pg_stat_statement

On Mon, Apr 7, 2014 at 4:19 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
>> I just noticed that this patch not only adds min,max,stddev, but it also
>> adds the ability to reset an entry's counters. This hasn't been
>> mentioned in this thread at all; there has been no discussion on whether
>> this is something we want to have, nor on whether this is the right API.
>
>> What it does is add a new function pg_stat_statements_reset_time() which
>> resets the min and max values from all function's entries, without
>> touching the stddev state variables nor the number of calls. Note
>> there's no ability to reset the values for a single function.
>
> That seems pretty bizarre. At this late date, the best thing would
> probably be to strip out the undiscussed functionality. It can get
> resubmitted for 9.5 if there's a real use-case for it.

If I'm understanding correctly, that actually seems reasonably
sensible. I mean, the big problem with min/max is that you might be
taking averages and standard deviations over a period of months, but
the maximum and minimum are not that meaningful over such a long
period. You might well want to keep a longer-term average while
seeing the maximum and minimum for, say, today. I don't know exactly
how useful that is, but it doesn't seem obviously dumb.

--
Robert Haas
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