Probabilistic Data Consistency for Wide-Area Applications

Wide-area applications, such as electronic commerce, groupware, directory service etc., rely on distributed data management services which often employ data replication to meet availability and response time constraints imposed by the target domains. Since many of these applications can tolerate some staleness in the data they access, the constraints may be better met by exploiting relaxed data consistency among copies in the system. However, in the current Internet architecture, it is nearly impossible to provide deterministic guarantees for the bounds on data inconsistency among copies. We present an approach for providing probabilistic data access guarantees while maintaining availability and timing predictability. Our model makes few assumptions regarding the underlying infrastructure. In fact, a novel feature of our approach is that it is independent of the underlying replication scheme. We focus on modeling the update patterns of the servers and modifying the data access mechanisms. Our model guarantees, with a certain probability P , that if a client requests the value of an object, the value returned by the system, if any, will be temporally consistent with the newest copy of the same object in the system. That is, from the perspective of a client, the system provides a probabilistic data consistency guarantee.