From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | ogjunk-pgjedan(at)yahoo(dot)com |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Costly "Sort Key" on indexed timestamp column |
Date: | 2004-09-10 04:17:11 |
Message-ID: | 14020.1094789831@sss.pgh.pa.us |
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Lists: | pgsql-performance |
<ogjunk-pgjedan(at)yahoo(dot)com> writes:
> I'm tuning my PostgreSQL DB (7.3.4) and have come across a query that
> doesn't use an index I created specially for it, and consequently takes
> circa 2 seconds to run. :(
> ...
> The output of EXPLAIN ANALYZE follows. Note how 99% of the total cost
> comes from "Sort Key: userinfo1_.create_date".
No, you are misreading the output. 99% of the cost comes from the join
steps.
I think the problem is that you have forced a not-very-appropriate join
order by use of INNER JOIN syntax, and so the plan is creating
intermediate join outputs that are larger than they need be. See
http://www.postgresql.org/docs/7.3/static/explicit-joins.html
7.4 is a bit more forgiving about this; compare
http://www.postgresql.org/docs/7.4/static/explicit-joins.html
regards, tom lane
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