Date: Tue, 1 Mar 2011 13:17:45 -0800
From: daveg <daveg@sonic.net>
To: David Christensen <david@endpoint.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>,
	Maxim Boguk <maxim.boguk@gmail.com>,
	Fujii Masao <masao.fujii@gmail.com>, pgsql-admin@postgresql.org,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Re: PD_ALL_VISIBLE flag was incorrectly set happend
	during repeatable vacuum
Message-ID: <20110301211745.GM26397@sonic.net>
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	<4D2D6A56.9060808@enterprisedb.com>
	<20110228212832.GH26397@sonic.net>
	<1B3CCBDD-4AC6-404A-9E26-DB4CA2554228@endpoint.com>
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On Mon, Feb 28, 2011 at 07:43:39PM -0600, David Christensen wrote:
> 
> On Feb 28, 2011, at 3:28 PM, daveg wrote:
> 
> > Anything new on this? I'm seeing at on one of my clients production boxes.
> > Also, what is the significance, ie what is the risk or damage potential if
> > this flag is set incorrectly?
> 
> 
> Was this cluster upgraded to 8.4.4 from 8.4.0?  It sounds to me like a known bug in 8.4.0 which was fixed by this commit:
> 
> commit 7fc7a7c4d082bfbd579f49e92b046dd51f1faf5f
> Author: Tom Lane <tgl@sss.pgh.pa.us>
> Date:   Mon Aug 24 02:18:32 2009 +0000
> 
>     Fix a violation of WAL coding rules in the recent patch to include an
>     "all tuples visible" flag in heap page headers.  The flag update *must*
>     be applied before calling XLogInsert, but heap_update and the tuple
>     moving routines in VACUUM FULL were ignoring this rule.  A crash and
>     replay could therefore leave the flag incorrectly set, causing rows
>     to appear visible in seqscans when they should not be.  This might explain
>     recent reports of data corruption from Jeff Ross and others.
>     
>     In passing, do a bit of editorialization on comments in visibilitymap.c.
> 
> oy:postgresql machack$ git describe --tag 7fc7a7c4d082bfbd579f49e92b046dd51f1faf5f
> REL8_4_0-190-g7fc7a7c
> 
> If the flag got twiddled while running as 8.4.0, the incorrect PD_ALL_VISIBLE flag would (obviously) not be fixed by the upgrade to 8.4.4.  (Is this a separate issue?)

This cluster was installed with 8.4.4. So it is still an existing problem.
Also, to my recollection, this cluster has never crashed.

-dg


-- 
David Gould       daveg@sonic.net      510 536 1443    510 282 0869
If simplicity worked, the world would be overrun with insects.