Date: Thu, 3 Mar 2011 02:53:46 -0800
From: daveg <daveg@sonic.net>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: 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>
Subject: Re: [HACKERS] Re: PD_ALL_VISIBLE flag was incorrectly set happend
	during repeatable vacuum
Message-ID: <20110303105346.GD4053@sonic.net>
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On Thu, Mar 03, 2011 at 10:16:29AM +0200, Heikki Linnakangas 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.

Thanks. I'll be applying this tomorrow and will send you some page images
to look at assuming it still does it.

I had a look at how this gets set and cleared and did not see anything obvious
so I'm pretty mystified. Also, we are seeing thousands of these daily for at
least a month on 4 large hosts and no-one has noticed any other issues,
which suprises me. Very strange.

-dg
 

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