| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> |
| Cc: | KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, Andrew Dunstan <andrew(at)dunslane(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Add min and max execute statement time in pg_stat_statement |
| Date: | 2013-10-21 20:01:41 |
| Message-ID: | 4338.1382385701@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> writes:
>>> If we're going to extend pg_stat_statements, even more than min and max
>>> I'd like to see the standard deviation in execution time.
> How about the 'median', often a lot more useful than the 'arithmetic
> mean' (which most people call the 'average').
AFAIK, median is impossible to calculate cheaply (in particular, with
a fixed amount of workspace). So this apparently innocent request
is actually moving the goalposts a long way, because the space per
query table entry is a big concern for pg_stat_statements.
regards, tom lane
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