Caching Proxies Limitations and Potentials

Abstract

As the number of World Wide Web users grows, so does the number of connections made to servers. This increases both network load and server load. Caching can reduce both loads by migrating copies ofserverfiles closer to the clients that use thosefiles. Caching can either be done at a client or in the network (by a proxy server or gateway). We assess the potential ofproxy servers to cache documents retrieved with the HTTP, GOPHER, FTP, and WATSprotocols using World Wide Web browsers. We monitored traffic corresponding to three types of educational workloads over a one-semesterperiod, and used this as input to a cache simulation. Our main findings are (1) that with our workloads a proxy has a 30-50% maximum possible hit rate no matter how it is designed; (2) that when the cache isfull and a document is replaced, classic least recently used (LRU) is apoorpolicy, but simple variations can dramatically improve hit rate and reduce cache size; (3) that a proxy server reallyfunctions as a second-level cache, and its hit rate may tend to decline with time after initial loading, given a more or less constant set ofusers; and (4) that certain modifications toproxy-server configuration parametersfor a cache may have little benefit.