| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Greg Stark <stark(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, "jd(at)commandprompt(dot)com" <jd(at)commandprompt(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Greg Smith <gsmith(at)gregsmith(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: benchmarking the query planner |
| Date: | 2008-12-12 09:04:35 |
| Message-ID: | 1229072675.13078.196.camel@hp_dx2400_1 |
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| Lists: | pgsql-hackers |
On Fri, 2008-12-12 at 02:23 +0000, Greg Stark wrote:
> The existing sampling mechanism is tied to solid statistics. It
> provides the correct sample size to get a consistent confidence range
> for range queries. This is the same mathematics which governs election
> polling and other surveys. The sample size you need to get +/- 5% 19
> times out of 20 increases as the population increases, but not by very
> much.
Sounds great, but its not true. The sample size is not linked to data
volume, so how can it possibly give a consistent confidence range?
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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