Comparing the performance of web server architectures

In this paper, we extensively tune and then compare the perfor-mance of web servers based on three different server architectures. The µserver utilizes an event-driven architecture, Knot uses the highly-efficient Capriccio thread library to implement a thread-per-connection model, and WatPipe uses a hybrid of events and threads to implement a pipeline-based server that is similar in spirit to a staged event-driven architecture (SEDA) server like Haboob. We describe modifications made to the Capriccio thread library to use Linux’s zero-copy sendfile interface. We then introduce the SYmmetric Multi-Processor Event Driven (SYMPED) architecture in which relatively minor modifications are made to a single pro-cess event-driven (SPED) server (the µserver) to allow it to con-tinue processing requests in the presence of blocking due to disk accesses. Finally, we describe our C++ implementation of WatPipe, which although utilizing a pipeline-based architecture, excludes the dynamic controls over event queues and thread pools used in SEDA. When comparing the performance of these three server ar-chitectures on the workload used in our study, we arrive at different conclusions than previous studies. In spite of recent improvements to threading libraries and our further improvements to Capriccio and Knot, both the event-based µserver and pipeline-based Wat-Pipe server provide better throughput (by about 18%). We also ob-serve that when using blocking sockets to send data to clients, the performance obtained with some architectures is quite good and in one case is noticeably better than when using non-blocking sockets