Summary Cache: A Scalable Wide-Area Web Cache Sharing Protocol

Li Fan, Pei Cao, Jussara Almeida, and Andrei Z. Broder
IEEE/ACM Trans. Netw., 8(3):281-293, 2000

Overview

This paper examines four different caching schemes:

• No Cache Sharing
• Simple Cache Sharing: Proxies serve each other's cache misses. Documents from other proxies are cached locally.
• Single-Copy Cache Sharing: Proxies serve each other's cache misses. Documents from other proxies are not cached locally, but the other proxy increases the document's caching priority
• Global Cache: Proxies share cache and coordinate replacement

These schemes are evaluated using five traces from different locations. Simple Cache Sharing achieves the highest hit ratio. This type of cache sharing is implemented by the Internet Cache Protocol (ICP). ICP has a high network overhead, because a proxy will query all its neighbors to find a cached object. This overhead is addressed by Summary Cache. With Summary Cache each cooperating proxy, keeps a summary of the cached objects at all other proxies. Bloom filters are used to create compact summaries. Summaries are updated whenever the number of new cached documents (not in the Bloom filter) reaches a threshold.