Project Description

WWW workload generators are used to evaluate web server performance, and thus have a large impact on what performance optimizations are applied to servers. However, current benchmarks ignore a crucial component: how these servers perform in the environment in which they are intended to be used, namely the wide-area Internet.

This project examines how WAN conditions can affect WWW performance. We study these effects using an experimental testbed which emulates WAN characteristics in a live setting, by introducing factors such as delay and packet loss in a controlled and reproducible fashion. We study how these factors interact with the host TCP implementation and what influence they have on web server performance. We demonstrate that when more realistic wide-area conditions are introduced, servers exhibit very different performance properties and scaling behaviors, which are not exposed by existing benchmarks running on LANs. We show that observed throughputs can give misleading information about server performance, and thus find that maximum throughput, or capacity, is a more useful metric. We find that packet losses can reduce server capacity by nearly 50 percent and increase response time as seen by the client. We show that using TCP SACK can reduce client response time, without reducing server capacity.

University Collaborations

• Carnegie Mellon University.