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Re: [HACKERS] Bad n_distinct estimation; hacks suggested?

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <gsstark(at)mit(dot)edu>,Marko Ristola <marko(dot)ristola(at)kolumbus(dot)fi>,pgsql-perform <pgsql-performance(at)postgresql(dot)org>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: [HACKERS] Bad n_distinct estimation; hacks suggested?
Date: 2005-04-26 20:45:53
Message-ID: 200504261345.54164.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Simon,

> Could it be that we have overlooked this simple explanation and that the
> Haas and Stokes equation is actually quite good, but just not being
> applied?

That's probably part of it, but I've tried Haas and Stokes on a pure random 
sample and it's still bad, or more specifically overly conservative.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

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