From: | Stephen Frost <sfrost(at)snowman(dot)net> |
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To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Peter Geoghegan <pg(at)heroku(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Add min and max execute statement time in pg_stat_statement |
Date: | 2013-10-23 16:20:38 |
Message-ID: | 20131023162038.GN2706@tamriel.snowman.net |
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Josh,
* Josh Berkus (josh(at)agliodbs(dot)com) wrote:
> On the other hand, it's still true that a high STDDEV indicates a high
> variance in the response times of a particular query, whereas a low one
> indicates that most are close to the average. While precision math
> might not work if we don't have the correct distribution, for gross DBA
> checks it's still useful. That is, I can answer the question in many
> cases of: "Does this query have a high average because of outliers, or
> because it's consisently slow?" by looking at the STDDEV.
The concern is actually the reverse issue- often the question is "is
this query ever really slow?", or "when is this query really slow?" and
those questions are not answered by stddev, min, max, nor avg.
> And FWIW, for sites where we monitor pg_stat_statements, we reset daily
> or weekly. Otherwise, the stats have no meaning.
I have wondered if we (PG) should do that by default.. I agree that
often they are much more useful when reset periodically. Of course,
having actual historical information *would* be valuable, if you could
identify the time range covered..
Thanks,
Stephen
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