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From:Egor Egorov Date:May 23 2003 3:36pm
Subject:re: MySQL using filesort :(
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On Friday 23 May 2003 18:11, Jason Hamilton wrote:
> At 11:01 AM 5/23/2003, Egor Egorov wrote:
> > > I'm having a problem with MySQL and ORDER BY.
> > >
> > > With this statement, extra = "Using where"
> > >
> > > EXPLAIN SELECT * FROM c1 LEFT JOIN c2 ON c1.id = c2.id WHERE c1.id =
> > > '21'
> > >
> > > Simply adding "ORDER BY c1.size DESC" changes the extra
> > > to "Using where; Using filesort".
> > >
> > > Naturally I have an index on c1.id (c2.id also has an index), and
> > > c1.size.
> > >
> > > I'm at a loss as to why it's going to filesort. The query speed
> > > is quick on most results, except for when there is > ~10,000 matches,
> > > then it can take several seconds to process. Most matches are
> > > under 1,000 results, though some can be as high as 150,000.
> > >
> > > Is there anything I can do to remove use of filesort, or increase
> > > the speed of the query on large matches?
> >
> >What version do you use? 3.23.xx ? If so, you can upgrade to 4.0.x. In
> > 4.0.x MySQL can use index in ORDER BY .. DESC queries.
>
> Egor,
>
> I'm running mysql-standard-4.0.12. The machine is a 2.4ghz server w/
> 1 gig of ram. I have been screwing around with the conf settings, heres
> some of the settings:

Do you have separate indexes on c1.id and c1.size or multi-column index on 
(c1.id, c1.size) ?



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  • MySQL using filesort :(Jason Hamilton23 May
    • re: MySQL using filesort :(Egor Egorov23 May
      • re: MySQL using filesort :(Jason Hamilton23 May
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        • re: MySQL using filesort :(Egor Egorov23 May
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