From: daveg <daveg@sonic.net>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Greg Stark <gsstark@mit.edu>
Cc: David Christensen <david@endpoint.com>
Cc: Maxim Boguk <maxim.boguk@gmail.com>
Cc: Fujii Masao <masao.fujii@gmail.com>
Cc: 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
Date: Thu, 3 Mar 2011 02:53:46 -0800
Message-ID: <20110303105346.GD4053@sonic.net> (raw)
In-Reply-To: <4D6F4E5D.6080507@enterprisedb.com>
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<4D2D6A56.9060808@enterprisedb.com>
<20110228212832.GH26397@sonic.net>
<1B3CCBDD-4AC6-404A-9E26-DB4CA2554228@endpoint.com>
<AANLkTi=xq4SV6jwA7txvrbEWocyeiU6XiTG=-zVy+7Dq@mail.gmail.com>
<AANLkTi=Ye7AoF7_uVQfPVn-ok2VOp65mi0xU3H7kCke3@mail.gmail.com>
<20110303071208.GA4053@sonic.net>
<4D6F4E5D.6080507@enterprisedb.com>
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.
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To: pgsql-admin@postgresql.org
Cc: daveg@sonic.net, heikki.linnakangas@enterprisedb.com, robertmhaas@gmail.com, gsstark@mit.edu, david@endpoint.com, maxim.boguk@gmail.com, masao.fujii@gmail.com, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Re: PD_ALL_VISIBLE flag was incorrectly set happend during repeatable vacuum
In-Reply-To: <20110303105346.GD4053@sonic.net>
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