Re: [HACKERS] Re: PD_ALL_VISIBLE flag was incorrectly set happend during repeatable vacuum

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(at)sss(dot)pgh(dot)pa(dot)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(at)sonic(dot)net 510 536 1443 510 282 0869
If simplicity worked, the world would be overrun with insects.