Question

Database is MySQL with MyISAM engine.

Table definition:

CREATE TABLE IF NOT EXISTS  matches  (
   id  int(11) NOT NULL AUTO_INCREMENT,
   game  int(11) NOT NULL,
   user  int(11) NOT NULL,
   opponent  int(11) NOT NULL,
   tournament  int(11) NOT NULL,
   score  int(11) NOT NULL,
   finish  tinyint(4) NOT NULL,
  PRIMARY KEY ( id ),
  KEY  game  ( game ),
  KEY  user  ( user ),
  KEY  i_gfu ( game , finish , user )
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=3149047 ;

I have set an index on (game, finish, user) but this GROUP BY query still needs 0.4 – 0.6 seconds to run:

SELECT user AS player
     , COUNT( id ) AS times
FROM matches
WHERE finish = 1
  AND game = 19
GROUP BY user
ORDER BY times DESC

The EXPLAIN output:

| id | select_type | table   | type | possible_keys | key   | key_len | 
|  1 |  SIMPLE     | matches |  ref | game,i_gfu    | i_gfu |    5    | 

|  ref        |   rows |   Extra                                      |
| const,const | 155855 | Using where; Using temporary; Using filesort |

Is there any way I can make it faster? The table has about 800K records.

---

EDIT: I changed COUNT(id) into COUNT(*) and the time dropped to 0.08 – 0.12 seconds. I think I’ve tried that before making the index and forgot to change it again after.

In the explain output the Using index explains the speeding up:

|   rows |   Extra                                                   |
| 168029 | Using where; Using index; Using temporary; Using filesort |

(Side question: is this dropping of a factor of 5 normal?)

There are about 2000 users, so the final sorting, even if it uses filesort, it doesn’t hurt performance. I tried without ORDER BY and it still takes almost same time.

Answer 1

The EXPLAIN verifies the (game, finish, user) index was used in the query. That seems like the best possible index to me. Could it be a hardware issue? What is your system RAM and CPU?