OSCAR: a system for weak-consistency replication

The proliferation of internetworks and distributed applications has increased the demand for geographically distributed replicated databases. The traditional approach of strong consistency is difficult to achieve across an internetwork. In contrast to strong consistency, a database replication system that provides weak consistency permits greater availability by allowing temporary inconsistencies to develop among the replicas. The Open System for Consistency and Replication (OSCAR), an architecture for a weak-consistency replication system, is presented. The approach to reliable replication is to use two complementary mechanisms. When an update initially enters the replication system, it is unreliably pushed to all other replicas. A novel technique called mediation ensures reliable propagation of the updates throughout the system. OSCAR provides appropriate weak consistency for a variety of applications by simultaneously supporting several weak-consistency methods. Its modular design permits its components to be configured for different networks and allows its algorithms to be selected and tuned for different environments and applications