Time-Domain Analysis of Web Cache Filter Effects (Extended Version)

This paper uses trace-driven simulation to study the traffic arrival process for Web workloads in a simple Web proxy caching hierarchy. Both empirical and synthetic Web proxy workloads are used in the study. The simulation results show that a Web cache reduces both the peak and the mean request arrival rate for Web traffic workloads, while the variance-to-mean ratio of the filtered traffic typically increases, depending on the input arrival process and the configuration of the cache. If the input traffic is self-similar, then the filtered request traffic remains self-similar, with the same Hurst parameter, though with reduced mean. Finally, we find that a Gamma distribution provides a flexible and robust means of modeling aggregate workloads in hierarchical Web caching architectures, for a broad range of workload characteristics and Web proxy cache sizes. To demonstrate the generality and effectiveness of the modeling approach, we present a detailed example of filter effects and traffic superposition in a two-level Web caching hierarchy with heterogenous input workloads. The Gamma modeling results match well with the results from trace-driven simulations.