Horton

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

Merlin Moncure <mmoncure@gmail.com>

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From: Merlin Moncure <mmoncure@gmail.com>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: daveg <daveg@sonic.net>, Robert Haas <robertmhaas@gmail.com>, Greg Stark <gsstark@mit.edu>, David Christensen <david@endpoint.com>, Maxim Boguk <maxim.boguk@gmail.com>, Fujii Masao <masao.fujii@gmail.com>, pgsql-admin@postgresql.org, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2011-03-03T15:04:04Z
Lists: pgsql-hackers

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  1. Fix a violation of WAL coding rules in the recent patch to include an

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On Thu, Mar 3, 2011 at 2:16 AM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> On 03.03.2011 09:12, daveg wrote:
>>
>> Question: what would be the consequence of simply patching out the setting
>> of this flag? Assuming that the incorrect PD_ALL_VISIBLE flag is the only
>> problem (big assumption perhaps) then simply never setting it would at
>> least
>> avoid the possibility of returning wrong answers, presumably at some
>> performance cost. We possibly could live with that until we get a handle
>> on the real cause and fix.
>
> Yes. With that assumption.
>
> If you really want to do that, I would suggest the attached patch instead.
> This just disables the optimization in seqscans to trust it, so an
> incorrectly set flag won't affect correctness of query results,  but the
> flag is still set as usual and you still get the warnings so that we can
> continue to debug the issue.

This.  The mis-set flag can is likely a bug/concurrency issue etc,
but could also be a symptom of more sinister data corruption.  I did
various vacuum experiments all day yesterday on my windows workstation
and was not able to produce any mis-flags.  I trust iscsi more than
nfs, but maybe there is a connection here that is hardware based.  hm.
do you think it would be helpful to know what is causing the
all_visible flag to get flipped?  If so, the attached patch shows
which case is throwing it...

merlin