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

On Mon, 05 Dec 2005 10:11:41 -0500, Tom Lane 
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