Skip site navigation (1) Skip section navigation (2)

Re: [HACKERS] 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: [HACKERS] Bad n_distinct estimation; hacks suggested?
Date: 2005-04-25 04:59:27
Message-ID: 10257.1114405167@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-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

In response to

pgsql-performance by date

Next:From: Steve PoeDate: 2005-04-25 06:58:16
Subject: Re: pgbench Comparison of 7.4.7 to 8.0.2
Previous:From: Richard PlotkinDate: 2005-04-25 03:13:47
Subject: Re: Disk filling, CPU filling, renegade inserts and deletes?

pgsql-hackers by date

Next:From: Tom LaneDate: 2005-04-25 05:07:44
Subject: Re: CVS regression test problem
Previous:From: Christopher Kings-LynneDate: 2005-04-25 02:47:14
Subject: Re: Old-style OR indexscan slated for destruction

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group