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Re: explain analyze results are different for each iteration

From: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
To: Robert Davis <robert(at)faithwestinc(dot)com>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: explain analyze results are different for each iteration
Date: 2004-09-15 02:07:17
Message-ID: 20040914190607.Y35716@megazone.bigpanda.com (view raw or flat)
Thread:
Lists: pgsql-sql
On Tue, 14 Sep 2004, Robert Davis wrote:

> I'm trying to benchmark some complex sql queries.  One query, in
> particular, is causing problems -- its cost values can vary from 228
> to 907, its Total Runtimes from 60 ms to 5176 ms.  The query plans
> show that the optimizer is choosing different plans for different
> iterations of the same query.  Does anyone have any idea what's
> going on here or maybe how I can force Postgres to prefer the faster
> plan?
>
> The query plans are very long (11 tables joined) but I can include
> them if it might help.  Thanks for any advice,

11 tables.  You might want to see if raising geqo_threshold stabilizes the
plans since IIRC that's the threshold for using the genetic optimizer.


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