From: Dennis Björklund <db@zigo.dhs.org>
To: Ben Chobot <bench@silentmedia.com>
Cc: PostgreSQL Performance <pgsql-performance@postgresql.org>
Subject: Re: 8.1 -> 8.4 regression
Date: Mon, 15 Feb 2010 10:40:49 +0100
Message-ID: <c50ac4425997cc51b9f371ae0214d90a.squirrel@zigo.org> (raw)
In-Reply-To: <0C60C7B5-B79F-444F-B8FB-EDD14E56F79E@silentmedia.com>
References: <0C60C7B5-B79F-444F-B8FB-EDD14E56F79E@silentmedia.com>
Can you force 8.4 to generate the same plan as 8.1? For example by running
SET enable_hashjoin = off;
before you run EXPLAIN on the query? If so, then we can compare the
numbers from the forced plan with the old plan and maybe figure out why it
didn't use the same old plan in 8.4 as it did in 8.1.
Note that the solution is not to force the plan, but it can give us more
information.
/Dennis
> is at least one query which has degraded in performance quite a bit. Here
> is the plan on 8.4.2:
> http://wood.silentmedia.com/bench/842
>
> Here is the very much less compact plan for the same query on 8.1.19:
> http://wood.silentmedia.com/bench/8119
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To: pgsql-performance@postgresql.org
Cc: db@zigo.dhs.org, bench@silentmedia.com
Subject: Re: 8.1 -> 8.4 regression
In-Reply-To: <c50ac4425997cc51b9f371ae0214d90a.squirrel@zigo.org>
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