5 Consistency Maintenance on the Mobile Grid Environment

In a replicated environment, same data are often distributed to several sites in order to improve the data availability, fault tolerance and faster access. However, when a replica is modified by a user, the other replicas become stale. In such situation a mechanism is needed to keep them consistent, which means all the replicated data have the same content. This can be achieved using a synchronization mechanism and it provides the same view of all the replicas by propagating the modifications done on the first replica to others. This process is usually called as update propagation which is the main part of the consistency mechanism. When replicas are read-only or when no consistency guarantees are required by the users of the replicated system, a synchronization system is not needed. In the present chapter, different replica synchronization techniques are studied. Also, based on the agent based framework proposed in the previous chapter an update propagation mechanism is proposed to provide consistency in the mobile grid environment.