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List:       postgresql-general
Subject:    Re: [GENERAL] Query performance inconsistant.
From:       Tom Lane <tgl () sss ! pgh ! pa ! us>
Date:       2006-08-31 20:43:27
Message-ID: 23754.1157057007 () sss ! pgh ! pa ! us
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Matthew Schumacher <matt.s@aptalaska.net> writes:
> I have "autovacuum = on" in the config file with a pretty frequent
> autovacuum_naptime, but I'm unsure if that does a vacuum or vacuum full.

autovacuum *never* does a vacuum full, because that would lead to
unexpected blockages of foreground queries.  Still though, autovac could
be contributing to the problem indirectly.  I'm assuming that most of
your transactions on the problem table are short.  It's possible that
one or more clients are grabbing quasi-exclusive table locks, and
normally you don't notice because they are able to get the lock quickly,
do their work, and get out.  But if autovac is working on the table then
the requestor of the exclusive lock blocks ... and everyone else queues
up behind him, until the vacuum command finishes with the table.

			regards, tom lane

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