Hybrid self-adaptive WWW cache coherence protocol (hSATTL): improving the coherence of WWW objects

Proxy caches in classical server-client architecture may decrease the amount of data transfer and reduce network congestion, hut they also impose a cache-coherence problem. Objects replicated in proxy caches must be kept coherent. Although various protocols for maintaining cache coherence in the World Wide Web (WWW) have been introduced, there does not exist a highly efficient solution to the coherence problem. We have designed a new hybrid self-adaptive protocol (hSATTL) for maintaining cache coherence. The protocol dynamically switches between three basic cache coherence mechanisms: server-oriented write-invalidate, server-oriented write-update, and proxy-oriented time-to-live (TTL). We describe the implementation of the hSATTL protocol and compare it to other currently used protocols. In order to perform measurements, we also develop a special software package. As performance measures, we use the level of coherence maintained by the protocols and the amount of network traffic generated by the protocols in order to maintain cache coherence.