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Re: Slow subquery on large dataset

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: bob_bamber(at)hotmail(dot)com (Bob)
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Slow subquery on large dataset
Date: 2004-02-21 06:58:52
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Lists: pgsql-novice
bob_bamber(at)hotmail(dot)com (Bob) writes:
> I'm having some performance issues when querying a couple of tables
> containing a large amount of data.

> foo=# SELECT data_id FROM capacity_data WHERE data_id NOT IN (SELECT
> data_id FROM capacities);

Try PG 7.4, or if you're on 7.4, try increasing sort_mem.  IN and NOT IN
have pretty sucky performance in earlier releases.  (If you can't
upgrade for some reason, you could try using EXISTS instead of IN.)

			regards, tom lane

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