From: Tom Lane <tgl@sss.pgh.pa.us>
To: Matt Clark <matt@ymogen.net>
Cc: pgsql-admin@postgresql.org
Subject: Re: Cost estimates consistently too high - does it matter?
Date: Fri, 08 Aug 2003 11:14:36 -0400
Message-ID: <26638.1060355676@sss.pgh.pa.us> (raw)
In-Reply-To: <OAEAKHEHCMLBLIDGAFELMEGBDGAA.matt@ymogen.net>
References: <OAEAKHEHCMLBLIDGAFELMEGBDGAA.matt@ymogen.net>
"Matt Clark" <matt@ymogen.net> writes:
> I've noticed that the cost estimates for a lot of my queries are
> consistently far to high.
You seem to be under a misapprehension. The cost estimates are not
in units of milliseconds, they are on an arbitrary scale with 1.0
defined as one disk fetch.
LIMIT throws another monkey wrench into the mix: the estimates for the
plan nodes underneath the limit are done as if the plan were to be
executed to completion, which of course it won't be.
regards, tom lane
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To: pgsql-admin@postgresql.org
Cc: tgl@sss.pgh.pa.us, matt@ymogen.net
Subject: Re: Cost estimates consistently too high - does it matter?
In-Reply-To: <26638.1060355676@sss.pgh.pa.us>
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