From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: pgsql-hackers@postgresql.org
Subject: Re: More thoughts about planner's cost estimates
Date: Thu, 1 Jun 2006 14:45:40 -0700
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Cc: Greg Stark <gsstark@mit.edu>,
 Tom Lane <tgl@sss.pgh.pa.us>
References: <14821.1149104747@sss.pgh.pa.us>
 <87u074g03a.fsf@stark.xeocode.com>
	<200606011350.26364.josh@agliodbs.com>
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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. =A0Actually, 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=20
columns, bytea and numerics with high precisions.  Also, we probably don't=
=20
need to correlate UNIQUE columns inside ... I think.

=2D-=20
=2D-Josh

Josh Berkus
PostgreSQL @ Sun
San Francisco