Re: More thoughts about planner's cost estimates - Mailing list pgsql-hackers

From Josh Berkus
Subject Re: More thoughts about planner's cost estimates
Date
Msg-id 200606011445.41158.josh@agliodbs.com
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In response to Re: More thoughts about planner's cost estimates  (Josh Berkus <josh@agliodbs.com>)
List pgsql-hackers
Greg,

> > 1) You have n^2 possible two-column combinations. That's a lot of
> > processing and storage.
>
> Yes, that's the hard problem to solve.  Actually, btw, it's n!, not n^2.

Ooops, bad math.  Andrew pointed out it's actually n*(n-1)/2, not n!.

Also, we could omit columns unlikely to correlate, such as large text
columns, bytea and numerics with high precisions.  Also, we probably don't
need to correlate UNIQUE columns inside ... I think.

--
--Josh

Josh Berkus
PostgreSQL @ Sun
San Francisco


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