Re: best statistic target for boolean columns - Mailing list pgsql-performance

From Josh Berkus
Subject Re: best statistic target for boolean columns
Date
Msg-id 200409271131.09932.josh@agliodbs.com
Whole thread Raw
In response to best statistic target for boolean columns  (Gaetano Mendola <mendola@bigfoot.com>)
Responses Re: best statistic target for boolean columns
List pgsql-performance
Gaetano,

> don't you think the best statistic target for a boolean
> column is something like 2?  Or in general the is useless
> have a statistics target > data type cardinality ?

It depends, really, on the proportionality of the boolean values; if they're
about equal, I certainly wouldn't raise Stats from the default of 10.   If,
however, it's very dispraportionate -- like 2% true and 98% false -- then it
may pay to have better statistics so that the planner doesn't assume 50%
hits, which it otherwise might.

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

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