OSSR: Optimal Single Site Replication

Replication is a technique widely used for achieving qualities like scalability, high performance, high availability and fault tolerance in computer systems. Consistency of the system state is another quality that may also vary as a side effect of replication. There are various configurations of replication architecture and of replica control protocols that provide various levels of these system qualities. In this paper we determine an optimal overall configuration, called the OSSR (Optimal Single Site Replication) Configuration, to maximize performance and scalability based on single site replication. We propose a corresponding OSSR Protocol that implements this configuration. The OSSR Protocol provides optimal or near optimal performance and scalability for both read and write intensive applications. While increased performance from existing replication protocols comes at the cost of reduced consistency, the OSSR Protocol provides a consistency guarantee good enough for most applications. We compare the performance and scalability of this protocol with three other protocols, each having a variation in one of the configuration parameters, to demonstrate its optimality.