This is just a quick note, incase it helps someone else in the future.

It seems that MySQL server, when using MyISAM tables doesn't truncate the index file when you run "ALTER TABLE x DISABLE KEYS", so when running "ALTER TABLE x ENABLE KEYS" you end up with an MyISAM index file (xxxx.myi) which keeps growing. In my case this hit 90gb on a customer's server.

Ways to fix this :

1. Upgrade to MySQL 5.0.52 (apparently ... see
   http://bugs.mysql.com/bug.php?id=4692 )
2. Run "optimize table xxxx"
3. Run "repair table xxxx quick use_frm"
4. Nuke it from orbit, it's the only way to be sure.

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