Proxy Cache Coherency and Replacement - Towards a More Complete Picture

This work studies the interaction of Web proxy cache coherency and replacement policies using trace-driven simulations. We specifically examine the relative importance of each type of policy in affecting the overall costs, the potential of incorporating coherency issues in cache replacement and the inclusion of additional factors such as frequency of resource use in replacement and coherency policies. The results show that the cache replacement policy in use is the primary cost determinant for relatively small caches, while the cache coherency policy is the determinant for larger caches. Incorporating cache coherency issues in cache replacement policies yields little improvement in overall performance. The use of access frequency in cache replacement, along with temporal locality and size information, results in a simple and better performing policy than found in previously published work. Combining this new replacement policy with the best piggyback-based cache coherency policy results in a 4.5% decrease in costs and 89% reduction in staleness ratio when compared to policy combinations in current use. Preliminary work indicates that cache replacement and coherency policies continue to affect costs in the presence of HTTP protocol enhancements such as persistent connections.