Maintaining consistency of database replicas

摘要

A replication protocol which includes associating a database version vector with each copy of the database in the system is provided. Each database version vector keeps track of the total number of updates to any data items in its respective database replica and from which server those updates were originally performed. During replication between two replicas, the database version vectors of the replicas are compared to efficiently determine if update replication is necessary. If the database version vectors are not identical, the server possessing the more recent version of the data items propagates those data items to the server whose replica is older using conventional update propagation techniques. Identical database version vectors indicate that update propagation is not necessary. As such, the protocol avoids examining every data item in the database in order to determine the necessity of update propagation, which is required in conventional replication protocols.