WebWave: globally load balanced fully distributed caching of hot published documents

Abstract

Document publication service over such a large network as the Internet challenges us to harness available server and network resources to meet fast growing demand. We show that large scale dynamic caching can be employed to globally minimize server idle time, and hence maximize the aggregate server throughput of the whole service. To be efficient, scalable and robust, a successful caching mechanism must have three properties: (1) maximize the global throughput of the system; (2) find cache copies without recourse to a directory service, or to a discovery protocol; and (3) be completely distributed in the sense of operating only on the basis of local information. We develop a precise definition, which we call tree load balance (TLB), of what it means for a mechanism to satisfy these three goals. We present an algorithm that computes TLB offline, and a distributed protocol that induces a load distribution that converges quickly to a TLB one. Both algorithms place cache copies of immutable documents on the routing tree that connects the cached document's home server to its clients, thus enabling requests to stumble on cache copies en route to the home server.