Re: MyISAM large tables and indexes managing problems

[Baron Schwartz]

Claudio,

http://www.mysqlperformanceblog.com/2007/10/29/hacking-to-make-alter-table-online-for-certain-changes/

Your mileage may vary, use at your own risk, etc.

Basically: convince MySQL that the indexes have already been built but
need to be repaired, then run REPAIR TABLE.  As long as the index is
non-unique, this can be done by sort.  In your case, the index
(PRIMARY) is unique, so you'll need to see if you can work around that
somehow.  Maybe you can create it under another name as non-unique,
build it, then swap it and the .frm file out.  Have fun.

This is the only option I see for you, but maybe there are others.