From: Brad Hilton <bhilton@vpop.net>
To: jasiek@serwer.skawsoft.com.pl
Cc: pgsql-sql@postgresql.org
Subject: Re: sub-query optimization
Date: 14 Feb 2003 11:42:27 -0800
Message-ID: <1045251747.29974.45.camel@aragorn.vpop.net> (raw)
In-Reply-To: <20030214192113.GA26987@serwer>
References: <1045246939.29966.22.camel@aragorn.vpop.net>
<20030214192113.GA26987@serwer>
On Fri, 2003-02-14 at 11:21, jasiek@serwer.skawsoft.com.pl wrote:
> Can you test these two queries?
Thanks, I'll test them shortly. I wanted to answer your other
questions, first:
> Can you say anything about data statistics in your tables? How
> many rows are with category_id=null?
>
> I looked into query definition once again. Your query doesn't make
> sense - article_categories have not null category_id... What do you really
> want to do?
Sorry to cause confusion. My original query and db format were fairly
complex so I didn't want to distract from my problem. My actual query
looks like:
select * from articles where exists
(select 1 from article_categories, categories, category_map
where
article_categories.article_id = articles.id and
categories.restrict_views = FALSE and
article_categories.category_id = categories.id and
category_map.parent_id = 1 and
category_map.child_id = categories.id and
category_map.child_id = article_categories.category_id and
articles.post_status = 'publish'
)
and
post_status = 'publish'
------------------
The problem is that sometimes there are no categories with
"restrict_views = FALSE" and the query takes a *long* time: 23 seconds.
However, if I simply add the 'articles' table to the inner query it
takes 0.23 msec.
*But*, sometimes there are many categories where "restrict_views =
FALSE", and in such a case adding the 'articles' table to the inner
query actually hurts performance quite a bit.
Does that help at all?
Thanks,
-Brad
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To: pgsql-sql@postgresql.org
Cc: bhilton@vpop.net, jasiek@serwer.skawsoft.com.pl
Subject: Re: sub-query optimization
In-Reply-To: <1045251747.29974.45.camel@aragorn.vpop.net>
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