From: Matt Clark <matt@ymogen.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-admin@postgresql.org
Subject: Re: Cost estimates consistently too high - does it matter?
Date: Fri, 8 Aug 2003 16:38:55 +0100
Message-ID: <OAEAKHEHCMLBLIDGAFELEEGIDGAA.matt@ymogen.net> (raw)
In-Reply-To: <26638.1060355676@sss.pgh.pa.us>
Well, I usually am under a misapprehension! Thanks for the explanation about LIMIT too.
In that case then, I shall stop worrying and learn to love the planner.
M
> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: 08 August 2003 16:15
> To: Matt Clark
> Cc: pgsql-admin@postgresql.org
> Subject: Re: [ADMIN] Cost estimates consistently too high - does it
> matter?
>
>
> "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: matt@ymogen.net, tgl@sss.pgh.pa.us
Subject: Re: Cost estimates consistently too high - does it matter?
In-Reply-To: <OAEAKHEHCMLBLIDGAFELEEGIDGAA.matt@ymogen.net>
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