Implementation and comparison of distributed caching schemes

Shared Web caches allow multiple clients to quickly access a pool of popular Web pages. An organization that provides shared caching to its Web clients will typically have a collection of shared caches rather than a single cache. If a collection of shared caches is used, it is required to coordinate the caches so that all cached pages in the collection are shared among the clients of the organization. In this paper, two protocol schemes for coordinating the collection of shared caches are investigated. The first scheme is based on the Internet caching protocol (ICP). In the ICP scheme, the Web caches query other caches for the Web pages and fetch the Web pages from the neighbors if they have cached the requested page. The second scheme is the hash routing scheme in which the client (browser) has to find the hash value for the URL of the requested page and send the request to the corresponding cache server. These two schemes have been implemented, and compared with respect to the page retrieval latency and the adaptability of the cache servers when a peer cache server fails. Our analysis shows that the hash routing schemes have significant performance advantages over ICP with respect to the average latency under normal conditions but when failure rate of the cache server is significant the ICP provides good adaptability. Also, we observe that the hashing function used in the hash routing scheme must have certain features such as quick calculation of the hash value and uniform distribution of the Web pages (among cache servers)