My assignment is B&S and it has cookie to lock and unlock record. So I don't need the client id benefit from RMI Connection Factory. I still try to use RMI Connection Factory because there is other benefit from it like only register once. However, I choose to return the same DvdDatabase instance to client because I can control the synchronization of record locking.
But according to Andrew's book, If two remote invocations share the same DvdDatabase instance, This can't ensure thread safety.