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The first task in Web testing is to use a tool to apply stress to the Web site and to measure the maximum requests per second that the Web server can handle. This is a quantitative measurement. The second task is to determine which resource prevents the requests per second from going higher, such as CPU, memory, or server dependencies. This second task takes more interpretation than the first.
In many situations, the Web server processor is the bottleneck. Increase the stress until the requests per second start to decrease, and then slightly reduce the stress. This level is the maximum performance that the Web site can achieve. You can increase the stress by increasing the Stress level setting (number of threads) or by increasing the number of Web Application Stress Tool client computer.
On the Web server, use System Monitor to watch the Computername; System; % Total Processor Time and Computername; Web Service; Connection Attempts/sec as well as Computername; Active Server Pages; and Requests Queued counters. If the processors are running at 80 to 85 percent of capacity, then they are most likely the bottleneck. If the number of Requests Queued fluctuates considerably during the stress test and the processor utilization remains relatively low, this indicates that the script is calling a server COM component that is receiving more calls than it can handle. In this case, the server COM component is the bottleneck.
You should determine an expected peak load that meets your business needs and then create a test that uses enough threads to reach that capacity. This will help you determine the maximum request rate for the Web application and confirm that it is in line with the expected peak load.
The amount of personalization in a Web application also plays a significant role in how it performs. The Web Application Stress Tool contains several features that make testing a personalized Web site easy. For example, you can create users, which allows the Web Application Stress Tool to save a cookie with each of them. You can also use the Querystring editor to help create and store several sets of name-value pairs that are passed with each request.