Replica Divergence Control Protocol in Weakly Connected Environment

This paper presents a consistency control protocol destined for groups of cooperative processes located worldwide. We assume that processes cooperate by sharing a replicated object. We consider processes with well-known profiles; however, the actual behaviour of each process could diverge from the profile. The protocol aims at offering a good quality of service to cooperative processes, while guaranteeing replicated object consistency in the presence of disconnections and network partitions. We are interested in the bounded consistency condition: the divergence between each replica and the “real object” remains smaller than a fixed bound during the lifetime of the application. We decompose this consistency condition into a set of local criteria concerning the effects of unexpected operations initiated by each process. We then associate with each process a consistency manager that enforces this process local consistency criterium. To experiment with this protocol, we developed a highly available allocation service relying on it. The experimental results confirm that this approach provides a high degree of autonomy to each replica, especially when the actual behaviour of that replica conforms to the profile.