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Re: [HACKERS] EXPLAIN ANALYZE on 8.2

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter Eisentraut <peter_e(at)gmx(dot)net>
Cc: pgsql-hackers(at)postgresql(dot)org, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Kelly Burkhart" <kelly(dot)burkhart(at)gmail(dot)com>, "Evgeny Gridasov" <eugrid(at)fpm(dot)kubsu(dot)ru>, pgsql-performance(at)postgresql(dot)org
Subject: Re: [HACKERS] EXPLAIN ANALYZE on 8.2
Date: 2006-12-15 15:57:25
Message-ID: 9227.1166198245@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> Am Freitag, 15. Dezember 2006 11:28 schrieb Simon Riggs:
>> Until we work out a better solution we can fix this in two ways:
>> 
>> 1. EXPLAIN ANALYZE [ [ WITH | WITHOUT ] TIME STATISTICS ] ...
>> 2. enable_analyze_timer = off | on (default) (USERSET)

> The second one is enough in my mind.

I don't see any point in either one.  If you're not going to collect
timing data then the only useful info EXPLAIN ANALYZE could provide is
knowledge of which rowcount estimates are badly off ... and to get that,
you have to wait for the query to finish, which may well be impractical
even without the gettimeofday overhead.  We had discussed upthread the
idea of having an option to issue a NOTICE as soon as any actual
rowcount exceeds the estimate by some-configurable-percentage, and that
seems to me to be a much more useful response to the problem of
"E.A. takes too long" than removing gettimeofday.

One thing that's not too clear to me though is how the NOTICE would
identify the node at which the rowcount was exceeded...

			regards, tom lane

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