Deferred-Update Replication Supporting Multiple Consistency Models

Many distributed systems use a replication mechanism for reliability and availability. On the other hand, developers have to consider minimum consistency requirement for each application. Therefore, a novel replication protocol that supports multiple consistency models is required. Multi-Consistency Data Replication (McRep) is a middleware-based replication protocol and can support multiple consistency models. However, McRep has a potential problem in that a replicator relaying all request and reply messages between clients and replicas can be a performance bottleneck and a single-point-of-failure. A deferred-update replication is a well-established approach for fault-tolerant data management systems but can only guarantee One-Copy Serializability. We apply the version control method of McRep to the deferred-update replication protocol to solve the problems. We extend client-side programs to store version numbers of their own transactions. We also extend the replica´s role to control version numbers to determine if a replica ensures a specified consistency model. We have implemented and evaluated both the proposed and the McRep protocols. The evaluation results show that the proposed protocol achieved comparable throughput of transactions to McRep. Especially the proposed protocol improved the throughput up to 16% at a read-heavy workload in One-Copy Serializability.