Understanding tuning complexity in multithreaded and hybrid web servers

Adequately setting up a multi-threaded Web server is a challenging task because its performance is determined by a combination of configurable Web server parameters and unsteady external factors like the workload type, workload intensity and machine resources available. Usually administrators set up Web server parameters like the keep-alive timeout and number of worker threads based on their experience and judgment, expecting that this configuration will perform well for the guessed uncontrollable factors. The nontrivial interaction between the configuration parameters of a multi-threaded Web server makes it a hard task to properly tune it for a given workload, but the burst nature of the Internet quickly change the uncontrollable factors and make it impossible to obtain an optimal configuration that will always perform well. In this paper we show the complexity of optimally configuring a multi-threaded Web server for different workloads with an exhaustive study of the interactions between the keep-alive timeout and the number of worker threads for a wide range of workloads. We also analyze the Hybrid Web server architecture (multi-threaded and event-driven) as a feasible solution to simplify Web server tuning and obtain the best performance for a wide range of workloads that can dynamically change in intensity and type. Finally, we compare the performance of the optimally tuned multithreaded Web server and the hybrid Web server with different workloads to validate our assertions. We conclude from our study that the hybrid architecture clearly outperforms the multi-threaded one, not only in terms of performance, but also in terms of its tuning complexity and its adaptability over different workload types. In fact, from the obtained results, we expect that the hybrid architecture is well suited to simplify the self configuration of complex application servers.