Weak Consistency Models for Replicated Data
Copy divergence; Weak memory consistency
Some designs for a distributed database system involve having several copies or replicas for a data item, at different sites, with algorithms that do not update these replicas in unison. In such a system, clients may detect a discrepancy between the copies. Each particular weak consistency model describes which discrepancies may be seen. If a system provides a weak consistency model, then the clients will require more careful programming than otherwise. Eventual consistency (q.v.) is the best-known weak consistency model.
In the late 1980s and early 1990s, replication research focused on systems that allowed replicas to diverge from one another in controlled ways. Epidemic or multi-master algorithms were introduced in the work of Demers et al. . These researchers identified the importance of session properties , which ensure that clients see information that includes changes they could reasonably...
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