Re: Vaccum Stalling

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Vaccum Stalling
Date: 2007-07-10 15:17:49
Message-ID: 19904.1184080669@sss.pgh.pa.us
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Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info> writes:
> Scenario - a large table was not being vacuumed correctly, there now ~
> 15 million dead tuples that account for approximately 20%-25% of the
> table. Vacuum appears to be stalling - ran for approximately 10 hours
> before I killed it. I hooked up to the process with gdb and this looks
> a bit suspicious to me.

Looks perfectly normal to me. Reads in btbulkdelete are exactly where
I'd expect 7.4's vacuum to be spending the bulk of its wait time on a
large table, because that's a logical-order traversal of the index, and
cannot benefit from any sequential-access advantage. (As of 8.2 we
are able to do this with a physical-order traversal, which can be a
whole lot faster.)

If you can afford to lock the table against writes for awhile,
reindexing might help by bringing the index back into physical order.

regards, tom lane

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