| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
| 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: | 2005-04-24 19:08:15 |
| Message-ID: | 200504241208.15437.josh@agliodbs.com |
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| Lists: | pgsql-hackers pgsql-performance |
Folks,
> I wonder if this paper has anything that might help:
> http://www.stat.washington.edu/www/research/reports/1999/tr355.ps - if I
> were more of a statistician I might be able to answer :-)
Actually, that paper looks *really* promising. Does anyone here have enough
math to solve for D(sub)Md on page 6? I'd like to test it on samples of <
0.01%.
Tom, how does our heuristic sampling work? Is it pure random sampling, or
page sampling?
--
Josh Berkus
Aglio Database Solutions
San Francisco
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