Distributed caching in unstructured peer-to-peer file sharing networks
Computers and Electrical Engineering
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File replication is widely used in structured P2P systems to avoid hot spots in servers and enhance file availability. The number of replicas and replication distance affect the file replication cost. These two elements and the replica update frequency determined in the file replication stage also affect the cost of subsequent consistency maintenance. However, most existing file replication protocols focus on improving file lookup efficiency without considering its cost and its subsequent influence on consistency maintenance. This paper studies the problem about how a server chooses files to replicate and where to replicate files to achieve low cost in both file replication and consistency maintenance stages without compromising the effectiveness of file replication. This paper presents a lightweight and Cooperative multifactOr considered file Replication Protocol (CORP) to achieve this goal. CORP simultaneously takes into account multiple factors including file popularity, update rate, node available capacity, file load, and node locality, aiming to minimize the number of replicas, update frequency, and replication distance. CORP also dynamically adjusts the number of replicas based on ever-changing file popularity and visit pattern. Extensive experimental results from simulation and PlanetLab real-world testbed demonstrate the efficiency and effectiveness of CORP in comparison with other file replication protocols. It dramatically reduces the overhead of both file replication and consistency maintenance. In addition, it exhibits high adaptiveness to skewed lookups and yields significant improvement in reducing overloaded nodes. Specifically, compared to the other replication protocols, CORP can reduce more than 71 percent of file replicas, 84 percent of overloaded nodes, 94 percent of consistency maintenance cost, and 72 percent of file replication and consistency maintenance latency.