Distributed proxy caches are an important tool for reducing Internet congestion and access latency. This paper gives an overview of research on distributed Web proxy caches in the CRISP project. The CRISP Web cache architecture is designed to allow the servers in a distributed cache to cooperate in an efficient and scalable way, by introducing a mapping service that maintains a global directory of objects in the cache. The mapping service consolidates the responsibility of responding to directory queries into an entity independent of the proxy caches themselves, enabling the mapping service to scale independently from the participating proxy caches.
We have described several alternative mapping sevice structures implemented in Crispy Squid, a modular extension to the popular Squid Cache. We have also described the Proxycizer, a general tool for empirical studies of Web cache structures under real observed workloads and controlled conditions.