performance with query

From: Alberto Dalmaso <dalmaso(at)clesius(dot)it>
To: pgsql-performance(at)postgresql(dot)org
Subject: performance with query
Date: 2009-06-16 13:37:42
Message-ID: 1245159462.5027.16.camel@dalmaso-opensuse.cl
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Hi everybody, I'm creating my database on postgres and after some days
of hard work I'm arrived to obtain good performance and owfull
performace with the same configuration.
I have complex query that perform very well with mergejoin on and
nestloop off.
If I activate nestloop postgres try to use it and the query execution
become inconclusive: after 3 hours still no answare so I kill the query.
Tht's ok but, with this configuration, very simple and little query like
"slect colum from table where primarykey=value bacome incredibly slow.
The only solutionI found at the momento is to set mergejoin to off
before doing this query.
That is an awfull solution because with that solution I have to change
all the software (a big, old software) in the (many) points in witch
this kind of query are used (the same problem to set to off mergejoin
for all the system and activate it on che connection that have to make
the hard query).
Do you have any suggestion to accelerate both complex and silply query?
I've tried a lot of configuration in enabling different "Planner Method
Configuration" but the only combination that really accelerate hard
query is mergejoin on and nestloop off, other settings seems to be
useless.
Thank's in advance.

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