Evaluating Web-Server Capacity
By Daniel A. Menascé and Virgilio A. F. Almeida
Company X was getting its e-commerce site ready for the holiday season. Management put together many promotions and gimmicks aimed at luring customers and making their e-shopping easier. The company expanded the online catalog with 40 percent more items deemed to sell well during that time of the year. It added attractive and colorful images of these items to entice customers. Sound files of CDs were also incorporated. Everything was ready to rake in the big profits. Enter holiday season. Sales were disappointing. "Why didn't customers visit our site?" asked management. Well, actually, customers tried but, in most cases, couldn't get in.
What went wrong? Well, in general, the site's IT infrastructure wasn't ready to support the increased traffic or the delivery of larger files such as images and sound files. The IT managers should have asked themselves questions such as: Is the bandwidth of the link connecting our site to the ISP large enough to support the traffic increase while maintaining acceptable service levels? Are the various servers -- HTTP, authentication, and database -- that support the e-commerce site properly sized to handle the new load? What percentage of connections will be rejected when the load increases? Where will the bottlenecks be during the holiday season? Should we have more computing power, more bandwidth, higher I/O bandwidth, or a different system configuration? These are typical capacity-planning questions. In this article we provide you with a roadmap to performing capacity planning for Web environments.
As more and more mission-critical applications are being supported by Web-based technologies, it becomes important to understand how to plan the capacity of Web sites to make sure that they deliver the expected quality of service.
