Database Replication Protocols

Databases are replicated in order to obtain two complementary features: performance improvement and high availability. Performance can be improved when a database is replicated since each replica can serve read-only accesses without requiring any coordination with the rest of replicas. Thus, when most of the application accesses to the data are read-only, they can be served locally without preventing other processes to access the same or other replicas. Moreover, a careful coordination management can ensure that the failure of one or more replicas does not compromise the availability of the database as long as at least one of the replicas is alive.