Followed the steps as said.
As expected indexes were there in the `show indexes from heavy` but the unexpected “disabled” comment.

I didn’t understand this behaviour!
They’re not at all disabled in the frm that I replaced.

Later I further tried::–

1. Check if indexes are used:-
mysql> explain select * from heavy where s_arid > 1000 and s_id>30000 limit 10;
+—-+————-+——-+——+—————+——+———+——+—–
—-+————-+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows
| Extra |
+—-+————-+——-+——+—————+——+———+——+—–
—-+————-+
| 1 | SIMPLE | heavy | ALL | NULL | NULL | NULL | NULL | 5000
000 | Using where |
+—-+————-+——-+——+—————+——+———+——+—–
—-+————-+
1 row in set (0.08 sec)

2.. If I need to do something extra??
mysql> analyze table heavy;
+————–+———+———-+———-+
| Table | Op | Msg_type | Msg_text |
+————–+———+———-+———-+
| lyrics.heavy | analyze | status | OK |
+————–+———+———-+———-+
1 row in set (0.03 sec)

mysql> optimize table heavy;
+————–+———-+———-+———-+
| Table | Op | Msg_type | Msg_text |
+————–+———-+———-+———-+
| lyrics.heavy | optimize | status | OK |
+————–+———-+———-+———-+
1 row in set (0.06 sec)

But nothing seemed working!

Later I read:
http://forums.mysql.com/read.php?21,66550,67204#msg-67204
and
http://dev.mysql.com/doc/refman/5.0/en/myisam-storage-engine.html

Is it the case that my index size is increased beyond limits and hence they’re disabled?

I tried this though instead changed a signed INT to an unsigned INT.

MySQL uses twos complement for negative ints and knowing that a table doesn’t contain any negative values, it was possible to just tell MySQL to use unsigned ints instead of signed without it needing to do anything.

On a test server, I ran::

(using world.sql)
mysql> FLUSH TABLE WITH READ LOCK;
mysql> ALTER TABLE City ENGINE=InnoDB;
mysql> CREATE TABLE Citytmp LIKE City;
mysql> ALTER TABLE Citytmp MODIFY ID INT UNSIGNED NOT NULL AUTO_INCREMENT;

# cp /var/lib/mysql/world/Citytmp.frm /var/lib/mysql/world/City.frm

mysql> UNLOCK TABLES;

I then did it on a customers box that had 2^31 rows in Innodb with a primary key of signed int which was the initial problem. it worked great!

ALTER TABLE accounts ALTER COLUMN cWork SET COMMENT ‘Foo’;

But the current structure is more like:

ALTER TABLE accounts ALTER COLUMN cWork cWork BIGINT(11) UNSIGNED NOT NULL COMMENT ‘Foo’;

And changing all that is just silly for something as minor as a comment change.