Optimistic active replication

Replication is a powerful technique for increasing availability of a distributed service. Algorithms for replicating distributed services do however face a dilemma: they should be: efficient (low latency); while ensuring consistency of the replicas, which are two contradictory goals. The paper concentrates on active replication, where all the replicas handle the clients´ requests. Active replication is usually implemented using the atomic broadcast primitive. To be efficient, some atomic broadcast algorithms deliberately sacrifice consistency, if inconsistency is likely to occur with a low probability. We present an algorithm that handles replication efficiently in most scenarios, while preventing inconsistencies. The originality of the algorithm is to take the client-server interaction into account, while traditional solutions consider atomic broadcast as a black box