Cooperative Caching Middleware for Cluster-Based Servers

We consider the use of cooperative caching to manage the memories of cluster-based servers. Over the last several years, a number of researchers have proposed locality-conscious servers that implement content-aware request distribution to address this problem [2, 17, 4, 5, 6]. During this development, it has become conventional wisdom that cooperative caching cannot match the performance of these servers [17]. Unfortunately, while locality-conscious servers provide very high performance, their request distribution algorithms are typically bound to specific applications. The advantage of building distributed servers on top of a block-based cooperative caching layer is the generality of such a layer; it can be used as a building block for diverse services, ranging from file systems to web servers. In this paper, we reexamine the question of whether a server built on top of a generic block-based cooperative caching algorithm can perform competitively with locality-conscious servers. Specifically, we compare the performance of a cooperative caching-based web server against L2S, a highly optimized locality-conscious server. Our results show that by modifying the replacement algorithm of traditional cooperative caching algorithms, we can achieve much of the performance provided by locality-conscious servers. Our modification increases network communication to reduce disk accesses, a reasonable trade-off considering the current trend of relative performance between LANs and disks.