From: Franck Routier <franck.routier@axege.com>
To: pgsql-performance@postgresql.org
Subject: Re: What happens between end of explain analyze and end of query execution ?
Date: Sat, 06 Apr 2013 11:05:11 +0200
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Le 05/04/2013 16:17, Tom Lane a écrit :
> What have you got the statistics targets set to in this database?
Ok, the problem definitely comes from the default_statistics_target
which is obviously too high on the database.
I have experimented with explain on queries with another set of 4 joined
tables.
In my first attempt, explain took more than 4 seconds (!)
Then I have set default_statistics_target to 100 and analyzed the 4
tables. Explain took a few ms.
Restored default_statistics_target to 5000, analyzed again. Explain took
1.8 seconds.
So, I seem to have two related problems: statistics are somewhat bloated
(as re-analyzing with same target takes the explain time from 4 sec down
to 1.8 sec).
And the target is far too high (as default target value take analyse
down to a few ms).
Now... can someone help me understand what happens ? Where can I look
(in pg_stats ?) to see the source of the problem ? maybe a column with a
huge list of different values the palnner has to parse ?
Regards,
Franck
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To: pgsql-performance@postgresql.org
Cc: franck.routier@axege.com
Subject: Re: What happens between end of explain analyze and end of query execution ?
In-Reply-To: <515FE547.3010301@axege.com>
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