Rare corruption of pg_class index

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I'm encountering some disconcerting problems on a 8.1.3 database.
Very occasionally, I get a "could not open relation with OID xxx".
This always occurs inside of a plpgsql function, and always refers
to a normal, stable table that has not been dropped. The first
time this occured, I reindexed the system indexes, but it has occured
again, and on more than one database, which seems to lessen the chance
of a hardware issue or a temporary index corruption issue. The functions
in question are called many times, but the error only happens once in
a blue moon. The last time it happened, the function ran with no problem
one minute before the error, and again four minutes afterwards. The
table name is hard-coded into the functions. This happens on average
five times a day or so, on a very busy database (> 10M statements/day,
the functions fire tens of thousands of times)

Any clues on what could be causing this, or ways to go forward on
debugging? Thanks.

- --
Greg Sabino Mullane greg(at)turnstep(dot)com
PGP Key: 0x14964AC8 200612201252
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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