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Re: [PERFORM] Bad n_distinct estimation; hacks suggested?
- 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: [PERFORM] Bad n_distinct estimation; hacks suggested?
- Date: Mon, 25 Apr 2005 00:59:27 -0400
- Message-id: <10257(dot)1114405167(at)sss(dot)pgh(dot)pa(dot)us>
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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- From: Tom Lane
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- Re: [PERFORM] Bad n_distinct estimation; hacks suggested?
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