Abstract: A system for maintaining the integrity of two substantially identical databases across a computer network consisting of two central processing units interconnected by a communications network includes means within a lock manager for maintaining a lock database on one of the central processing units, means within an application program for initiating a request for a lock to be placed on an identified entity in both of the databases to enable a data update transaction to be performed on the identified entity in both of the databases, and means within the lock manager for locking the identified entity in both of the databases by establishing an entry for the identified entity in the lock database.