Scalable Web Caching of Frequently Updated Objects Using Reliable Multicast

Frequently updated web objects reduce the benefit of caching, increase the problem of cache inconsistency, and aggravate the inefficiency of the conventional "repeated unicast" delivery model. In this paper, we investigate multicast invalidation and delivery of popular, frequently updated objects to web cache proxies. Our protocol, MMO, groups objects into volumes, each of which maps to one IP multicast group. We show that, by forming volumes of the appropriate size and/or object correlation, the benefit from reliable multicast outweighs the cost of delivering extraneous data as well as the overhead of multicast reliability. Moreover, trace-driven simulations show that the bandwidth saving over conventional approaches increases significantly as the audience size grows. We conclude that MMO provides efficient bandwidth utilization and service scalability, and makes strong web cache consistency for dynamic objects practical.