The effects of wide-area conditions on WWW server performance

Erich M. Nahum, Marcel-Catalin Rosu, Srinivasan Seshan, Jussara Almeida
2001 Performance Evaluation Review  
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 widearea Internet. This paper shows how WAN conditions can affect WWW server performance. We examine these effects using an experimental testbed which emulates WAN characteristics in a live
more » ... ting, 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 widearea 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 as much as 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. ¥ How does server performance scale with load? ¥ How do packet delay and loss affect observed throughput? ¥ What is the impact of loss and delay on response time as seen by the client? ¥ How do TCP variants such as SACK and New Reno influence performance? ¥ How do delay and loss affect server capacity? We evaluate 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. The testbed consists of a cluster of PCs acting as clients, connected via a switched LAN to a high-performance web server. We show that when more realistic wide-area conditions are introduced, servers exhibit very different performance properties and
doi:10.1145/384268.378790 fatcat:zqgv2ro6gnaoxnb3zoq4otxeji