From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ken <postgres@kwasnicki.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: update query taking 24+ hours
Date: Sun, 14 Jan 2007 14:30:32 -0500
Message-ID: <12574.1168803032@sss.pgh.pa.us> (raw)
In-Reply-To: <45A9CEA3.3020903@kwasnicki.com>
References: <45A9CEA3.3020903@kwasnicki.com>
Ken <postgres@kwasnicki.com> writes:
> I have postgres 8.1 on a linux box: 2.6Ghz P4, 1.5GB ram, 320GB hard
> drive. I'm performing an update between two large tables and so far
> it's been running for 24+ hours.
> UPDATE Master SET val2=Import.val WHERE Master.x=Import.x AND
> Master.y=Import.y;
What does EXPLAIN say about that? (Don't try EXPLAIN ANALYZE,
but a plain EXPLAIN should be quick enough.)
> Both tables have indexes on the x and y columns. Will that help?
A two-column index would have helped a lot more, probably, although
with so many rows to process I'm not sure that indexes are useful
anyway. For really bulk updates a hashjoin or sort-and-mergejoin
plan is probably the best bet.
BTW, both of those would require plenty of work_mem to run fast
... what have you got work_mem set to?
And possibly even more to the point, do you have any foreign key
constraints leading into or out of the Master table?
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, postgres@kwasnicki.com
Subject: Re: update query taking 24+ hours
In-Reply-To: <12574.1168803032@sss.pgh.pa.us>
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