Piggyback Cache Validation for Proxy Caches in the World Wide Web

This paper attempts to tackle the cache coherency problem for documents without an expiration time. Rather than use a strictly weak or strong cache consistency approach, we piggyback cache state information onto HTTP requests to a server. In the simplest approach, whenever a proxy cache has a reason to communicate with a server it piggybacks on a list of cached documents for which the expiration time is unknown. This mechanism can reduce the number of requests and connections between a proxy cache and a server, while providing close to strongly consistent cache information. Alternatives that we are considering could also be used to provide a more cost eeective server invalidation mechanism.