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Re: Rare corruption of pg_class index

From: "Greg Sabino Mullane" <greg(at)turnstep(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Rare corruption of pg_class index
Date: 2007-01-04 22:12:03
Message-ID: 9cb1bf20123451c04260e3405735aa19@biglumber.com (view raw or flat)
Thread:
Lists: pgsql-hackers
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Tom Lane replied:
>> So as a general rule, the system tables should be considered a special
>> case as far as transactional activity? To be more precise, you are saying
>> that a system table must be locked in access exclusive mode before any
>> change is made to guarantee no problems occur?

> No, I didn't say that --- I said that you need to lock the table whose
> schema you're trying to modify, to ensure that no one else is in the
> midst of accessing it using the old schema info.

Sorry, I did mean the target table.

>> So the oft-given advice of "UPDATE pg_class SET relhasrules = false"
>> is actually completely unsafe unless the entire referenced table is
>> completely locked, and unless you are using at least 8.2?

> I don't recall having ever given *that* advice to anyone.  But yes,
> it's unsafe if there might be concurrent access to that table.  The
> only context I've ever seen people use this sort of thing in is
> pg_restore --disable-triggers, and in that situation I think there's
> an implicit assumption that no one else is busy modifying the table
> you're restoring into.

Not, not your advice, and perhaps not as common as SET reltriggers, but
still invaluable for things like bulk loading. Thanks for the responses,
I think I've finally got my head around the problem. At the very least,
I've discovered another good reason to push production sites to use
8.2.

- --
Greg Sabino Mullane greg(at)turnstep(dot)com
End Point Corporation
PGP Key: 0x14964AC8 200701041708
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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