Re: Improving N-Distinct estimation by ANALYZE - Mailing list pgsql-hackers

From Josh Berkus
Subject Re: Improving N-Distinct estimation by ANALYZE
Date
Msg-id 200601061526.14436.josh@agliodbs.com
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In response to Re: Improving N-Distinct estimation by ANALYZE  (Greg Stark <gsstark@mit.edu>)
Responses Re: Improving N-Distinct estimation by ANALYZE  (Greg Stark <gsstark@mit.edu>)
Re: Improving N-Distinct estimation by ANALYZE  (Simon Riggs <simon@2ndquadrant.com>)
List pgsql-hackers
Greg,

> These numbers don't make much sense to me. It seems like 5% is about as
> slow as reading the whole file which is even worse than I expected. I
> thought I was being a bit pessimistic to think reading 5% would be as
> slow as reading 20% of the table.

It's about what *I* expected.  Disk seeking is the bane of many access 
methods.

Anyway, since the proof is in the pudding, Simon and I will be working on 
some demo code for different sampling methods so that we can debate 
results rather than theory.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco


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