WebMonitor: a Tool for Measuring World-Wide Web Server Performance

Server performance has become a crucial issue for improving the overall performance of the World-Wide Web. This paper describes WebMonitor, a tool for evaluating and understanding server performance, and presents new results for realistic workloads. WebMonitor measures activity and resource consumption, both within the kernel and in HTTP processes running in user space. WebMonitor is implemented using an efficient combination of sampling and event-driven techniques that exhibit low overhead. Our initial implementation is for the Apache World-Wide Web server running on the Linux operating system. We demonstrate the utility of WebMonitor by measuring and understanding the performance of a Pentium-based PC acting as a dedicated WWW server. Our workloads use file size distributions with a heavy tail. This captures the fact that Web servers must concurrently handle some requests for large audio and video files, and a large number of requests for small documents, containing text or images. Our results show that in a Web server saturated by client requests, up to 90% of the time spent handling HTTP requests is spent in the kernel. These results emphasize the important role of operating system implementation in determining Web server performance. It also suggests the need for new operating system implementations that are designed to perform well when running on Web servers