Re: Queries taking ages in PG 8.1, have been much faster in PG<=8.0

From: Manfred Koizar <mkoi-pg(at)aon(dot)at>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Markus Wollny" <Markus(dot)Wollny(at)computec(dot)de>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Queries taking ages in PG 8.1, have been much faster in PG<=8.0
Date: 2005-12-10 17:14:00
Message-ID: m42mp11sic0p8ach6n4jkiieccqfok98cu@4ax.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-performance

On Mon, 05 Dec 2005 10:11:41 -0500, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
wrote:
>> Correlation -0.0736492
>> Correlation -0.237136

>That has considerable impact on the
>estimated cost of an indexscan

The cost estimator uses correlationsquared. So all correlations
between -0.3 and +0.3 can be considered equal under the assumption
that estimation errors of up to 10% are acceptable.
Servus
Manfred

In response to

Browse pgsql-performance by date

  From Date Subject
Next Message Greg Stark 2005-12-11 06:12:08 Re: Bitmasks
Previous Message Ivan Voras 2005-12-10 17:12:58 Bitmasks