From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: pgsql-performance@postgresql.org
To: Chris Kratz <chris.kratz@vistashare.com>
Subject: Re: Ramifications of turning off Nested Loops for slow queries
Date: Tue, 04 Mar 2008 10:18:43 -0600
Message-ID: <47CD2203.EE98.0025.0@wicourts.gov> (raw)
In-Reply-To: <483ACAF5-A485-40D9-9D7E-7008EF12F909@vistashare.com>
References: <483ACAF5-A485-40D9-9D7E-7008EF12F909@vistashare.com>
>>> On Tue, Mar 4, 2008 at 8:42 AM, in message
<483ACAF5-A485-40D9-9D7E-7008EF12F909@vistashare.com>, Chris Kratz
<chris.kratz@vistashare.com> wrote:
> So, I've now been asked to ping the list as to whether turning off
> nested loops system wide is a bad idea, and why or why not.
In our environment, the fastest plan for a lot of queries involve
nested loops. Of course, it's possible that these never provide the
fasted plan in your environment, but it seems very unlikely --
you're just not noticing the queries where it's doing fine.
> Any other thoughts or suggestions?
Make sure your effective_cache_size is properly configured.
Increase random_page_cost and/or decrease seq_page_cost.
You can play with the cost settings on a connection, using EXPLAIN
on the query, to see what plan you get with each configuration
before putting it into the postgresql.conf file.
-Kevin
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To: pgsql-performance@postgresql.org
Cc: Kevin.Grittner@wicourts.gov, chris.kratz@vistashare.com
Subject: Re: Ramifications of turning off Nested Loops for slow queries
In-Reply-To: <47CD2203.EE98.0025.0@wicourts.gov>
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