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Re: performance with query

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: "Alberto Dalmaso" <dalmaso(at)clesius(dot)it>, pgsql-performance(at)postgresql(dot)org
Subject: Re: performance with query
Date: 2009-06-18 19:39:21
Message-ID: 15037.1245353961@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> With all the optimizer options on, and the from_collapse_limit and
> join_collapse_limit values both set to 100, run an EXPLAIN (no
> ANALYZE) on your big problem query.  Let us know how long the EXPLAIN
> runs.  If it gets any errors, copy and paste all available
> information.  (General descriptions aren't likely to get us very far.)
> Since EXPLAIN without ANALYZE only *plans* the query, but doesn't run
> it, it should not take long to do this.

One issue here is that with the collapse limits cranked up to more than
geqo_threshold, he's going to be coping with GEQO's partially-random
plan selection; so whatever he reports might or might not be especially
reflective of day-to-day results.  I'm tempted to ask that he also push
up geqo_threshold.  It's possible that that *will* send the planning
time to the moon; but it would certainly be worth trying, to find out
what plan is produced.

			regards, tom lane

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Subject: Re: Strange performance response for high load times
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