Using the small-world model to improve Freenet performance

Efficient data retrieval in a peer-to-peer system like Freenet is a challenging problem. We study the impact of cache replacement policy on the performance of Freenet. We find that, with Freenet´s LRU (least recently used) cache replacement, there is a steep reduction in the hit ratio with increasing load. Based on intuition from the small-world models and the recent theoretical results by Kleinberg, we propose an enhanced-clustering cache replacement scheme for use in place of LRU. Such a replacement scheme forces the routing tables to resemble neighbor relationships in a small-world acquaintance graph - clustering with light randomness. In our simulation, this new scheme improved the request hit ratio dramatically while keeping the small average hops per successful request comparable to LRU. A simple, highly idealized model of Freenet under clustering with light randomness proves that the expected message delivery time in Freenet is O(log²n) if the routing tables satisfy the small-world model and have the size θ(log²n).