Timed Buffers: A Technique For Update Propagation In Nomadic Environments

Optimistic replication algorithms allow data presented to users to be stale (non up to date) but in a controlled way: they propagate updates in background and allow any replica to be accessed directly most of the time. When the timely propagation of updates to remote distributed replicas is an important issue, it is preferable that a replica gets the same update twice than it does not receive it at all. On the other hand, few assumptions on the topology of the network can be made in a nomadic environment, where connections are likely to change unpredictably. An extreme approach would be to blindly ``push'' every update to every replica; however, this would lead to a huge waste of bandwidth and of resources. In this paper we present a novel approach based on timed buffers, a technique that tends to reduce the overall number of propagated updates while guaranteeing that every update is delivered to every replica and that the propagation is not delayed.