Re: Slow performance with no apparent reason

Please supply EXPLAIN ANALYZE output.

On Sun, Oct 26, 2003 at 12:25:37AM +0300, Yonatan Goraly wrote:
> I am in the process of adding PostgreSQL support for an application, in
> addition to Oracle and MS SQL.
> I am using PostgreSQL version 7.3.2, Red Hat 9.0 on Intel Pentium III board.
>
> I have a query that generally looks like this:
>
> SELECT t1.col1, t2.col1 FROM t1, t2 WHERE t1.x=t2.y AND t2.p='string'
> AND t2.q=1
>
> This query is strikingly slow (about 100 sec when both t1 and t2 has
> about 1,200 records, compare with less than 4 sec with MS SQL and Oracle)
>
> The strange thing is that if I remove one of the last 2 conditions
> (doesn't matter which one), I get the same performance like with the
> other databases.
> Since in this particular case both conditions ( t2.p='string', t2.q=1)
> are not required, I can't understand why having both turns the query so
> slow.
> A query on table t2 alone is fast with or without the 2 conditions.
>
> I tired several alternatives, this one works pretty well:
>
> SELECT t1.col1, t2.col1 FROM t1, t2 WHERE t1.x=t2.y AND
> EXISTS (
> SELECT * FROM t2 t2a WHERE t2a.p='string' AND t2a.q=1 AND
> t2a.y=t2.y )
>
> Since the first query is simpler than the second, it seems to me like a bug.
>
> Please advise
>
> Yonatan

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Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
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