Performance modeling of an Apache Web server with a dynamic pool of service processes

In the current Internet the performance of service delivery crucially depends on the proper and efficient operation of Web servers. It is determined by their software architecture and characterized by the applied processing model. Here we consider the Unix software architecture of an Apache Web server with its non-threaded multi-processing module Prefork. We propose a tractable multi-server model to approximate the performance of the load-dependent dynamic behavior of Apache's resource pool of available HTTP service processes, which has not been done before. Furthermore, we show that this Markovian queueing model can be solved by advanced matrix-geometric methods. Then the efficiently computed performance results of this analytic model are compared with measurements of a real Apache Web server. The outcome clearly indicates that our analytic model can very accurately predict the mean-value performance of Apache under the Prefork policy.