Summary cache

TLDR

Sharing caches among Web proxies can reduce traffic and alleviate bottlenecks, but existing protocols impose too much overhead for widespread deployment. This paper introduces the Summary Cache protocol, designed to enable efficient cache sharing among proxies. Each proxy maintains a compact, periodically updated summary of the URLs cached by its peers—requiring as little as 8 bits per entry—and consults these summaries before issuing any cache queries. Trace‑driven simulations and a prototype demonstrate that Summary Cache cuts inter‑cache messages by 25–60×, bandwidth use by over 50 %, and CPU overhead by 30–95 %, while preserving the hit ratio of the Internet Cache Protocol and allowing many proxies to share caches.

Abstract

The sharing of caches among Web proxies is an important technique to reduce Web traffic and alleviate network bottlenecks. Nevertheless it is not widely deployed due to the overhead of existing protocols. In this paper we propose a new protocol called "Summary Cache"; each proxy keeps a summary of the URLs of cached documents of each participating proxy and checks these summaries for potential hits before sending any queries. Two factors contribute to the low overhead: the summaries are updated only periodically, and the summary representations are economical --- as low as 8 bits per entry. Using trace-driven simulations and a prototype implementation, we show that compared to the existing Internet Cache Protocol (ICP), Summary Cache reduces the number of inter-cache messages by a factor of 25 to 60, reduces the bandwidth consumption by over 50%, and eliminates between 30% to 95% of the CPU overhead, while at the same time maintaining almost the same hit ratio as ICP. Hence Summary Cache enables cache sharing among a large number of proxies.