Proactive Replication and Search for Rare Objects in Unstructured Peer-to-Peer Networks

The search efficiency problem in unstructured peer-to-peer network has not been adequately addressed so far, especially concerning search for rare objects. In this paper, we propose a proactive replication strategy to improve the search efficiency for rare objects. It uses object probing technique for peers to decide whether to establish replications for their objects or not when they join the network. This strategy can effectively increase the popularity of rare objects so as to enhance the search efficiency. We also present a rare object search algorithm. When a peer forwards a search request, forward probability is calculated according to its neighbors’ degree and the number of neighbors’ objects. Therefore, the search request is forwarded to the peers more likely containing target objects. Simulations show that the proactive replication strategy greatly improves the search efficiency for rare objects with moderate communication overhead. The rare object search algorithm not only improves search efficiency for rare objects, but also achieves load balance in search.