Received: from maia.hub.org (maia-3.hub.org [200.46.204.243])
	by mail.postgresql.org (Postfix) with ESMTP id EDF3BB5D90E
	for <pgsql-hackers-postgresql.org@mail.postgresql.org>;
	Sun, 29 May 2011 11:40:39 -0300 (ADT)
Received: from mail.postgresql.org ([200.46.204.86])
	by maia.hub.org (mx1.hub.org [200.46.204.243]) (amavisd-maia,
	port 10024) with ESMTP id 79314-09
	for <pgsql-hackers-postgresql.org@mail.postgresql.org>;
	Sun, 29 May 2011 14:40:33 +0000 (UTC)
X-Greylist: from auto-whitelisted by SQLgrey-1.7.6
Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130])
	by mail.postgresql.org (Postfix) with ESMTP id CE337B5D8BD
	for <pgsql-hackers@postgresql.org>;
	Sun, 29 May 2011 11:40:32 -0300 (ADT)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
	by sss.pgh.pa.us (8.14.2/8.14.2) with ESMTP id p4TEeRt0019877;
	Sun, 29 May 2011 10:40:27 -0400 (EDT)
To: =?ISO-8859-1?Q?C=E9dric_Villemain?= <cedric.villemain.debian@gmail.com>
cc: Greg Stark <gsstark@mit.edu>, Robert Haas <robertmhaas@gmail.com>,
	Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	Florian Helmberger <fh@25th-floor.com>,
	Alvaro Herrera <alvherre@commandprompt.com>, pgsql-hackers@postgresql.org
Subject: Re: [ADMIN] pg_class reltuples/relpages not updated by
	autovacuum/vacuum
In-reply-to: <BANLkTimbSiUZC7+ZZJOzMWp=M2jYZZcJSg@mail.gmail.com> 
References: <4DD28F73.6010108@25th-floor.com> <25017.1306291669@sss.pgh.pa.us>
	<4DDCA801.70805@25th-floor.com> <19738.1306338472@sss.pgh.pa.us>
	<BANLkTi=973Arh-nXLO6YFP7_ZTCeNp-X7w@mail.gmail.com>
	<22497.1306341699@sss.pgh.pa.us>
	<BANLkTi=jcKSU5zR+JG2BvfLNCtezC9sb+g@mail.gmail.com>
	<15043.1306423500@sss.pgh.pa.us>
	<BANLkTikrCaoZCVrda6SNCUQFiYvvZX75BA@mail.gmail.com>
	<25097.1306426982@sss.pgh.pa.us>
	<BANLkTikxM6V5DUsXnDEs84z=oRMbyeoOgA@mail.gmail.com>
	<4DDE475B020000250003DD63@gw.wicourts.gov>
	<BANLkTikTbZ8gibj+X++vkdqkxxJCU6trWw@mail.gmail.com>
	<4DDE5033020000250003DD71@gw.wicourts.gov>
	<BANLkTikGu30z1rwYeN0NwuO8jMFWHzus+Q@mail.gmail.com>
	<4DDE7EB8020000250003DDA8@gw.wicourts.gov>
	<9007.1306446600@sss.pgh.pa.us>
	<BANLkTinREie2cX2zqZPSEfUsZsdM+GjymQ@mail.gmail.com>
	<28116.1306609295@sss.pgh.pa.us>
	<BANLkTi=6RYvEVfKn8ufPEf9meGVEu=fHsQ@mail.gmail.com>
	<11295.1306645848@sss.pgh.pa.us>
	<BANLkTimbSiUZC7+ZZJOzMWp=M2jYZZcJSg@mail.gmail.com>
Comments: In-reply-to =?ISO-8859-1?Q?C=E9dric_Villemain?=
	<cedric.villemain.debian@gmail.com>
	message dated "Sun, 29 May 2011 10:40:28 +0200"
Date: Sun, 29 May 2011 10:40:27 -0400
Message-ID: <19876.1306680027@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Virus-Scanned: Maia Mailguard 1.0.1
X-Spam-Status: No, hits=-1.91 tagged_above=-5 required=5 tests=BAYES_00=-1.9,
	T_RP_MATCHES_RCVD=-0.01
X-Spam-Level: 
X-Archive-Number: 201105/1493
X-Sequence-Number: 188527

=?ISO-8859-1?Q?C=E9dric_Villemain?= <cedric.villemain.debian@gmail.com> writes:
> 2011/5/29 Tom Lane <tgl@sss.pgh.pa.us>:
>> OK, do you like the attached version of that logic?  (Other fragments
>> of the patch as before.)

> The idea was that remove only one page from the VACUUM will prevent
> relfrozenxid update and reltuples (and relpages) update.
> Now, I beleive that once we've skip at least one page thanks to
> SKIP_PAGES_THRESHOLD, then we should be more agressive and remove as
> many as possible pages from the VACUUM, tks to the VM.

That would require proof, not just suggestion.  Skipping pages will
defeat the OS read-ahead algorithm, and so could easily cost more than
reading them.

			regards, tom lane