Consistency Management in Optimistic Replication Algorithms

Optimistic replication algorithms allow replica contents to become stale but in a controlled way. In return, they become far more efficient and available than traditional replication algorithms that keep all the replicas consistent, especially when the network and computers are unreliable. The use of optimistic replication has grown explosively due to the proliferation of the use of the Internet and mobile computing devices, but its systematic study has begun only recently. This report surveys optimistic replication algorithms. In particular, it focuses on mechanisms for propagating updates among replicas and studies how they affect the functional characteristics of the systems, including data consistency guarantees and performance.