Re: Slow query

You are right. I rewrote the query using JOINs and it increased
performance from 123 sec. to 20msec. I betcha I screwed smth up, but I
list the rewritten query below anyways. I also attached the new plan.
Thank you.

SELECT * FROM media m
JOIN
((SELECT objectid AS mediaid
FROM media
WHERE activity='347667')
UNION
(SELECT ism.media AS mediaid
FROM intsetmedia ism, set s
WHERE ism.set = s.objectid
AND s.activity='347667' )) a1
ON
m.mediatype = (SELECT objectid FROM mediatype WHERE medianame='Audio')
AND m.objectid=mediaid
ORDER BY medianame ASC, status DESC



-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Monday, March 24, 2003 3:09 PM
To: Oleg Lebedev
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Slow query


Oleg Lebedev <oleg.lebedev@waterford.org> writes:
> I just ran the query you sent me and attached the output of EXPLAIN
> ANALYZE as TOMs_plan.txt It did not speed up the query significantly.

Nope.  I was hoping to see a faster-start plan, but given the number of
rows involved I guess it won't change its mind.  You're going to have to
think about a more intelligent approach, rather than minor tweaks.

One question: since objectid is evidently a primary key, why are you
doing a subselect for the first part?  Wouldn't it give the same result
just to say "m.activity = '347667'" in the top-level WHERE?

As for the second part, I think you'll have to try to rewrite it as a
join with the media table.

            regards, tom lane



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