Session-based admission control: a mechanism for improving performance of commercial Web sites

We introduce a new, session-based workload for measuring Web server performance. We define a session as a sequence of client individual requests. We then measure server throughput as a number of successfully completed sessions. Using a simulation model we show that an overloaded Web server can experience a severe loss of throughput measured as a number of completed sessions compared with the server throughput measured in requests per second. Moreover statistical analysis of completed sessions reveals that the overloaded Web server discriminates against longer sessions. We introduce a session-based admission control (SBAC) to prevent a Web server from becoming overloaded and to ensure that longer sessions can be completed. We show that a Web server augmented with the admission control mechanism is able to provide a fair guarantee of completion, for any accepted session, independent of session length. This provides a predictable and controllable platform for Web applications, and is a critical requirement for any E-business.