From:
Nathan Boley <npboley(at)gmail(dot)com>
To:
Robert Haas <robertmhaas(at)gmail(dot)com>
Cc:
PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>, pgsql-hackers Hackers <pgsql-hackers(at)postgresql(dot)org>, Boszormenyi Zoltan <zb(at)cybertec(dot)at>
Subject:
Re: WIP: cross column correlation ...
Date:
2011-02-23 05:50:50
Message-ID:
AANLkTimLFwakAxeSvjBwBo_sdzGrbeBP9a=BrDkDLn6O@mail.gmail.com (view raw or flat )
Thread:
2011-02-22 19:48:47 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
2011-02-23 01:58:00 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-23 02:43:59 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2011-02-23 02:56:37 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-23 03:04:12 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2011-02-23 08:15:39 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
2011-02-23 14:48:13 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-23 14:54:11 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
2011-02-23 22:37:39 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-23 05:50:50 from Nathan Boley <npboley(at)gmail(dot)com>
2011-02-23 14:46:34 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-23 14:56:59 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
2011-02-23 08:02:28 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
2011-02-23 15:10:07 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-23 22:40:00 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-24 20:42:39 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-25 06:33:59 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-25 13:18:40 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-25 16:45:43 from Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>
2011-02-25 17:50:51 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-25 22:35:45 from Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>
2011-02-25 17:03:58 from Rod Taylor <rod(dot)taylor(at)gmail(dot)com>
2011-02-25 19:26:10 from Alvaro Herrera <alvherre(at)commandprompt(dot)com>
2011-02-26 05:24:26 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-28 18:44:08 from Alvaro Herrera <alvherre(at)commandprompt(dot)com>
2011-03-01 00:18:43 from Rod Taylor <rod(dot)taylor(at)gmail(dot)com>
2011-02-26 13:38:31 from Rod Taylor <rod(dot)taylor(at)gmail(dot)com>
2011-02-27 07:59:44 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-25 23:41:09 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-26 05:29:14 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-26 06:57:54 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-26 14:46:55 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-27 08:03:10 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-27 17:44:35 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-27 22:17:49 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-28 15:13:39 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-28 18:04:54 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-28 18:19:46 from Martijn van Oosterhout <kleptog(at)svana(dot)org>
2011-02-28 18:24:13 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-28 18:31:29 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-28 18:50:03 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2011-02-28 18:54:23 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-28 19:31:53 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2011-02-28 19:37:23 from Michael Glaesemann <grzm(at)seespotcode(dot)net>
2011-02-28 19:39:19 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-28 19:47:23 from "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
2011-02-28 20:02:30 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2011-03-02 12:29:59 from Bernd Helmle <mailings(at)oopsware(dot)de>
2011-02-28 20:24:41 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-03-01 08:50:25 from Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>
2011-02-28 19:47:22 from Euler Taveira de Oliveira <euler(at)timbira(dot)com>
2011-02-28 20:03:33 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2011-02-28 21:13:47 from Greg Stark <gsstark(at)mit(dot)edu>
2011-02-28 22:05:08 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-28 22:52:00 from Chris Browne <cbbrowne(at)acm(dot)org>
2011-02-28 22:35:28 from Robert Treat <rob(at)xzilla(dot)net>
2011-02-26 09:33:14 from Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl>
2011-02-26 14:45:24 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-26 18:12:42 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
2011-02-26 18:44:52 from Greg Stark <gsstark(at)mit(dot)edu>
2011-02-26 18:58:20 from Martijn van Oosterhout <kleptog(at)svana(dot)org>
2011-02-26 20:10:46 from Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl>
2011-02-27 08:01:18 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-27 17:24:43 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-24 01:09:10 from Josh Berkus <josh(at)agliodbs(dot)com>
2011-02-24 03:11:11 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-24 03:30:08 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-24 03:58:08 from Robert Haas <robertmhaas(at)gmail(dot)com>
2011-02-24 15:07:35 from Bruce Momjian <bruce(at)momjian(dot)us>
2011-02-24 06:13:36 from PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>
Lists:
pgsql-hackers
> Personally, I think the first thing we ought to do is add a real, bona
> fide planner hint to override the selectivity calculation manually,
> maybe something like this:
>
> WHERE (x < 5 AND y = 1) SELECTIVITY (0.1);
>
If you're going to go that far, why not just collect statistics on
that specific predicate?
ie, ANALYZE SELECTIVITY ON tablename (x, y) WHERE (x < 5 AND y = 1);
Then it won't fall subject to all of the pitfalls that Tom outlines below.
Selectivities are easy to estimate if we know the predicate. They only
become hard when they have to work for every possible predicate.
Best,
Nathan
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