You have not mentioned the use of a multiple column index, for that matter,
no indexes at all. I would suggest a multiple column index in the form of
hidden, touser. That index form should speed up your queries and solve the
----- Original Message -----
From: "Fagyal Csongor" <concept@stripped>
To: "Dirk Schippers" <Dirk.Schippers@stripped>
Sent: September 14, 2004 12:24 PM
Subject: [Bulk] Re: MySQL speed
> > Hello,
> > For several years I am hosting a popular website using PHP and MySQL.
> > As the site is growing and evolving, speed is becoming more and more
> > important.
> > With my latest inventions on the website, I notice that the website is
> > becoming slow and I want to find out what's causing this.
> > And this is the question that makes me totally confused:
> > How is it possible that the following query:
> > "SELECT COUNT(*) FROM messages WHERE touser = 20 AND hidden = 0" with
> > a key on touser can take up to 1 second (I even had moments where it
> > would take up to 18 seconds!!!) even if EXPLAIN says mysql only has to
> > walk trough 2500 rows thanks to the key on touser. (Oh yeah, I did an
> > ANALYSE on the table)
> > If I think of making my own program walking trough a datafile with
> > 2500 items, checking every item for the flag "hidden" I would think
> > that should not take up to even 0.01 second! Of course MySQL is more
> > complicated than this, but I think it still is a very big difference.
> > More information: table messages is an MyISAM table of 48MB which has
> > 67000 rows, a primary key on id, a key on touser and a key on isread
> > with the following fields: id - bigint(20) autoincrement, fromuser -
> > int(10) unsigned, touser - int(10) unsigned, ts - datetime, message -
> > text, isread - tinyint(1) unsigned, ipnumber - varchar(20), hidden -
> > tinyint(1).
> > I experience this problem also with other tables and queries but as
> > this is the most simple one, I show this one as an example.
> > So: is it normal that the difference is so big, and that tables which
> > are not so very big (I think 67000 rows, or 48MB is not that huge for
> > a good database) are so hard to find rows into, keeping in mind that
> > the key makes the query only walk trough 2500 rows? Or is this normal?
> Just some ideas for you.
> 1: I think you should use "CHAR" instead of "VARCHAR". Might take more
> place, but using fixed length fields in general mean faster access time.
> 2: To walk through 2500 rows might take some time, as the "hidden"
> fields for each rows must be fetched (IMHO).
> 3: You should use query caching. That might speed up your query
> 4: You can try a hack: instead of using a field do denote that a user is
> not hidden, you might want to consider using some other method, e.g.
> using a signed integer for userid, and storing inactive users with a
> negative userid. Then you could count on users "where userid > 0".
> - Csongor Fagyal
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