deleting with cascades - performance?

[Adam Hardy]

I've got a performance issue doing deletes. I have a simple model where a 
grandparent, parent, child, grandchild relationship exists, with one grandparent 
having 2 or 3 thousand grandchildren. I delete the parent and cascade it down 
the relationships to delete the whole lot.

This takes 5 mins on a 1.6GHz Core2 machine.
I'm just doing this:

entityManager.remove(grandparent);

Is there a better way or do I just have to put some indices on the database? I 
thought standard foreign key constraints acted as indices in databases - isn't 
that so?

Thanks
Adam