From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: Nested loops overpriced
Date: Thu, 10 May 2007 17:35:06 +0200
Message-ID: <200705101735.06509.peter_e@gmx.net> (raw)
In-Reply-To: <28620.1178732406@sss.pgh.pa.us>
References: <200705081722.16731.peter_e@gmx.net>
<200705091817.45056.peter_e@gmx.net>
<28620.1178732406@sss.pgh.pa.us>
Am Mittwoch, 9. Mai 2007 19:40 schrieb Tom Lane:
> Hmmm ... I see at least part of the problem, which is that email_header
> is joined twice in this query, which means that it's counted twice in
> figuring the total volume of pages competing for cache space. So the
> thing thinks cache space is oversubscribed nearly 3X when in reality
> the database is fully cached.
I should add that other, similar queries in this database that do not involve
joining the same table twice produce seemingly optimal plans. (It picks hash
joins which are actually faster than nested loops.)
--
Peter Eisentraut
http://developer.postgresql.org/~petere/
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To: pgsql-performance@postgresql.org
Cc: peter_e@gmx.net, tgl@sss.pgh.pa.us
Subject: Re: Nested loops overpriced
In-Reply-To: <200705101735.06509.peter_e@gmx.net>
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