FloodTrail: an efficient file search technique in unstructured peer-to-peer systems

Searching efficiency is a decisive factor concerning scalability in large-scale peer-to-peer (P2P) file sharing systems. While flooding is the most commonly used and user-performance oriented method to broadcast query across an unstructured P2P network, it generates a large number of redundant messages. Our study shows that more than 70% of messages are redundant using flooding in a moderately connected network, which imposes an increasingly excessive burden on the underlying infrastructure, hindering the growth and scalability of P2P systems. To reduce the use of flooding as well as its associated overhead, we utilize the access trail left by a standard flooding, which is a collection of P2P links used by non-redundant messages. Thus the multiple queries following the flooding can be broadcasted along the trail to achieve two goals: (1) The ability of flooding to achieve short response time is maintained; (2) the cost of a broadcast is minimized. Though the trail can be partially damaged in an ad hoc system with constant peer arrivals and departures, we used repeated trail refreshings and additional trail links to make a trail consistently available for query broadcast. We call this trail-based technique FloodTrail. We evaluated the performance of FloodTrail for P2P systems for Web