Creating and maintaining replicas in unstructured peer-to-peer systems

Abstract

In peer-to-peer systems, replication is an important issue as it improves search performance and data availability. It has been shown that optimal replication is attained when the number of replicas per item is proportional to the square root of their popularity. In this paper, we focus on updates in the case of optimal replication. In particular, we propose a new practical strategy for achieving square root replication called pull-then-push replication (PtP). With PtP, after a successful search, the requesting node enters a replicate-push phase where it transmits copies of the item to its neighbors. We show that updating the replicas can be significantly improved through an update-push phase where the node that created the copies propagates any updates it has received using similar parameters as in replicate-push. Our experimental results show that replicate-push coupled with an update-push strategy achieves good replica placement and consistency with small message overhead. © Springer-Verlag Berlin Heidelberg 2006.