The value n may be 1 or 0:
1 (true) - When a Primary Key constraint is specified, it does not also become the IDKey index in the class definition.
0 (false) - A Primary Key constraint specified also becomes the IDKey index in the class definition; this generally gives better performance, but means that the Primary Key fields cannot be updated.
0 or 1. The default is 1.
On the page System Administration > Configuration > SQL and Object Settings > General SQL Settings, for the Are Primary Keys Created through DDL not ID Keys setting, choose Yes (true) or No (false).