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Re: strange behavior (corruption?) of large production

From: Joe Conway <mail(at)joeconway(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Hackers (PostgreSQL)" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: strange behavior (corruption?) of large production
Date: 2005-12-03 00:17:23
Message-ID: 4390E413.9030602@joeconway.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:
> Joe Conway <mail(at)joeconway(dot)com> writes:
> 
>>So they agree in template1 and cyspec databases.
> 
> OK, in that case I'd wonder about whether you've suffered XID wraparound
> in pg_database and/or pg_shadow.  The typical symptom of this is that
> entries are valid from the system's point of view but not visible to
> queries, and that seems to be what you have.  If so, a restart will NOT
> fix it.  You could try a VACUUM FREEZE on pg_database though.  Before
> doing that, I'd suggest looking at the rows' xmin values (use
> pg_filedump or grovel through the bits by hand) to confirm the
> wraparound theory.
> 

Talking to the maintainer of this cluster, it sounds like XID wraparound 
could be the problem. I thought they were running database wide vacuums 
at some regularity, but apparently they are only vacuuming specific 
production tables.

Since this is a production machine, putting pg_filedump on it may be 
problematic -- if I grovel through the bits by hand, can you give me a 
hint about what to look for?

Thanks,

Joe



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