Re: performance with query

From: Alberto Dalmaso <dalmaso(at)clesius(dot)it>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-performance(at)postgresql(dot)org
Subject: Re: performance with query
Date: 2009-06-17 15:11:21
Message-ID: 1245251481.5027.142.camel@dalmaso-opensuse.cl
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That what i send is the quick execution, with other parameters this
query simply doesn't come to an end.
It is the little query that changing the settings (using the default
with all the query analyzer on) becames really quick, while with this
settings (with some analyzer switched off) became very slow.

I don't belleve: using this settings

set enable_hashjoin = 'on';
set enable_nestloop = 'on';
set enable_seqscan = 'on';
set enable_sort = 'on';

set from_collapse_limit = 8;
set join_collapse_limit = 3;

select * from v_fsa_2007_estrazione;
finnally end in acceptable time (156 sec)
what does it mean using join_collapse_limit = 3 (that is really a lot of
object less that what i'm using in taht query).

I'm executing an explain analyze in this new situation...
It is possible that such a configuration can create performance problem
on other queryes? (join_collapse_limit is set to a really low value)

I'll made some test in this direction.

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