More fun with partitions, this time with MyISAM

mysql> CREATE TABLE t1 (id INT PRIMARY KEY ) 
             engine=myisam PARTITION BY HASH(id) PARTITIONS 1000;
Query OK, 0 rows affected (0.18 sec)

mysql> alter table t1 add column v int;
ERROR 1016 (HY000): Can't open file: './test/t1.frm' (errno: 24)

mysql> quit
Bye

$ perror 24
OS error code  24:  Too many open files

Looks as if MyISAM tries to open all the 1000 partition .MYD/.MYI files at once and runs out of file handles during this operation ...