HASH ROUTING FOR COLLECTIONS OF SHARED WEB CACHES

Shared Web caches, also referred to as proxy Web servers, allow multip le clients to quickly access a pool of popular Web pages. An organizat ion that provides shared caching to its Web clients will typically hav e a collection of shared caches rather than lust one. For collections of shared caches, ii is desirable to coordinate the caches so that all cached pages in the collection are shared among the organization's cl ients. In this article we investigate two classes of protocols for coo rdinating a collection of shared caches: the ICP protocol, which has c aches ping each other to locate a cached object; and the hash routing protocols, which place objects in the shared caches as a function of t he objects' URLs. Our contribution is twofold. First, we compare the p erformance of the protocols with respect to cache-server overhead and object retrieval latency; for a collection of shared caches, our analy sis shows that the hash-routing schemes have significant performance a dvantages over ICP for both of the performance metrics. The existing h ash-routing protocols assume that the cache servers are homogeneous in storage capacity and processing capability, even though most collecti ons of cache servers are vastly heterogeneous. Our second contribution is to extend a robust hash-routing scheme so that it balances request s among the caches according to any desired distribution; the extended hash-routing scheme is robust in the face of cache failures, is tunab le for heterogeneous caches, and can have significant performance adva ntages over ICP.