Using multiple replica classes to improve performance in distributed systems

Replication has been primarily used as a means of increasing availability in distributed systems. It is known that replication can mitigate the costs of accessing remotely stored data in distributed systems. Replication control protocols in the literature have stopped short of addressing availability and performance concerns. These issues are addressed by contributing a classification of replicas with each class having different consistency requirements. Metareplicas keep track of up-to-date replicas for recently accessed objects and changes in data reference localities. Thus they allow many transaction operations to synchronously execute at only a single (and often local) replica. Pseudoreplicas are non-permanent replicas that facilitate localized execution of transaction operations. True replicas are permanent replicas that increase the availability of operations and data