Optimal Replacement Policies for Non-Uniform Cache Objects with Optional Eviction

摘要

Replacement policies for general caching applications and Web caching in particular have been extensively addressed in the literature. Many policies that focus on document costs, size, probability of references, and temporal locality of requested documents, have been proposed. In many cases these policies are ad-hoc attempts to take advantage of the statistical information contained in the stream of requests, and to address the factors above. However, since the introduction of optimal replacement policies for conventional caching, the problem of finding optimal replacement policies under the factors indicated has not been studied in any systematic manner. In this paper, the authors take a step in that direction. They first show, under the Independent Reference Model, that a simple Markov stationary replacement policy, called the policy C(sub 0), minimizes the long-run average metric induced by nonuniform document costs when document eviction is optional. They then use these results to propose a framework to operate caching systems with multiple performance metrics. They do so by solving a constrained caching problem with a single constraint. The resulting constrained optimal replacement policy is obtained by simple randomization between two Markov stationary optimal replacement policies, but induced by different costs.