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

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