Horton

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

Manfred Koizar <mkoi-pg@aon.at>

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From: Manfred Koizar <mkoi-pg@aon.at>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: "Markus Wollny" <Markus.Wollny@computec.de>, pgsql-performance@postgresql.org
Date: 2005-12-10T17:14:00Z
Lists: pgsql-performance 
On Mon, 05 Dec 2005 10:11:41 -0500, Tom Lane <tgl@sss.pgh.pa.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