| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | Manfred Koizar <mkoi-pg(at)aon(dot)at>, Andrew Dunstan <andrew(at)dunslane(dot)net>, 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: | 2005-04-25 04:59:27 |
| Message-ID: | 10257.1114405167@sss.pgh.pa.us |
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| Lists: | pgsql-hackers pgsql-performance |
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> Tom, how does our heuristic sampling work? Is it pure random sampling, or
> page sampling?
Manfred probably remembers better than I do, but I think the idea is
to approximate pure random sampling as best we can without actually
examining every page of the table.
regards, tom lane
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