Peter Phaal

Session-based admission control: a mechanism for peak load management of commercial Web sites

We consider a new, session-based workload for measuring web server performance. We define a session as a sequence of clients individual requests. 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 against the server throughput measured in requests per second. Moreover, statistical analysis of completed sessions reveals that the overloaded web server discriminates against longer sessions. For e-commerce retail sites, longer sessions are typically the ones that would result in purchases, so they are precisely the ones for which the companies want to guarantee completion. To improve Web QoS for commercial Web servers, 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 a session length. This provides a predictable and controllable platform for web applications and is a critical requirement for any e-business. Additionally, we propose two new adaptive admission control strategies, hybrid and predictive, aiming to optimize the performance of SBAC mechanism. These new adaptive strategies are based on a self-tunable admission control function, which adjusts itself accordingly to variations in traffic loads.

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.

Peak load management for commercial Web servers using adaptive session-based admission control

We use a session-based workload to measure the performance of a commercial Web server. We define a session as a sequence of client requests. An overloaded Web server can experience a severe loss of throughput when measured as the number of completed sessions. Moreover, the overloaded Web server discriminates against longer sessions. Session based admission control (SBAC), introduced in (Cherkasova and Phaal, 1998; 1999), prevents a Web server from becoming overloaded and ensures that longer sessions can be completed. We propose two new adaptive admission control strategies: hybrid and predictive, aiming to optimize the performance of the SBAC mechanism. The hybrid strategy is based on a self-tunable admission control function, which adjusts itself accordingly to variations in traffic loads. It shows improved performance results for workloads with medium to long average session length. The predictive strategy estimates and predicts the number of new sessions it can accept and still guarantee processing of all future session requests. It consistently shows the best performance results for different workloads and different traffic loads.