Testing and Tuning Applications

One of the benefits of running your Web servers in a cluster is that the impact of a slow running application is alleviated. Unfortunately, this only serves to hide an application performance issue; it doesn't fix the problem.

Before you deploy an application to a production server, it should be tested, not only for bugs and memory leaks, but for performance as well.

Anticipating Application Load

To properly test an ASP application you have to determine what type of load is anticipated for the application. We recommend that you break this load down as follows:

• Total number of unique application users—You can use the total of hits per month or, for more granularity, the total number of hits per hour.
• Total number of concurrent users—You should base this number on peak time usage.
• Peak request rate—You should determine how many pages need to be served per second in a worst-case scenario.

Determining the Total Number of Users

In a production environment, it may be difficult to determine the total number of users and concurrent users for the application. For Internet sites, you should:

• Break down the IIS server logs to segment usage data.
• Take a best guess at how much traffic the site is likely to attract.
• Project a worst-case usage scenario.

If your site is primarily for intranet use, you should:

• Break down the IIS server logs to segment usage data.
• Try to determine who is using the site. Is everyone or a selected group of users? Calculate how many computers are on the corporate network, and try to identify usage peaks.
• Project a worst-case scenario.

Stress Test the Application

After you've established a context for testing, you can use the WAS tool to run test scripts against the server. This tool enables you to simulate different types and degrees of user load and collect performance data.

You can download the newest version of the tool from the WAS Tool site at http://webtool.rte.microsoft.com. While you're at the site, you should also download the white paper "Web Application Stress Test and Data Analysis." Prepared by the Unisys Consulting Service, this paper documents the work they did for an enterprise customer who wanted them to assess and analyze the scalability and performance of a Web application that made extensive use of SQL Server 7.0 stored procedures. The customer's goals included determining the appropriate hardware platform for hosting the application, addressing potential performance bottlenecks, and estimating the typical response time that the application's users could expect.

We also recommend the following print-based resources for optimizing, testing, and tuning your ASP applications:

• Reilly and Gibbs, Chapter 26, "Optimizing ASP Performance," Professional Active Server Pages 3.0, WROX Press, October 1999.
• Appendix A, "ASP Best Practices," in the Internet Information Services 5.0 Resource Guide, Microsoft Press, 2000.

Table 10.8 lists several additional online resources that deal with Web application performance and tuning.

Table 10.8 Application Performance Resources

Title	Author	Location
25+ ASP Tips to Improve Performance and Style		http://msdn.microsoft.com/workshop/server/asp/asptips.asp
Server Performance and Scalability Killers	George Reilly	http://msdn.microsoft.com/workshop/server/iis/tencom.asp
Maximizing the Performance of Your Active Server Pages	Nancy Winnick Cluts	http://msdn.microsoft.com/workshop/server/asp/maxperf.asp
Got Any Cache?	Nancy Winnick Cluts	http://msdn.microsoft.com/workshop/server/feature/cache.asp
Tips to Improve ASP Application Performance	Srinivasa Sivakumar	http://www.15seconds.com/issue/000106.htm
Timing the Execution Time of Your ASP Scripts	Mike Shaffer	http://www.4guysfromrolla.com/webtech/122799-1.shtml
Testing the Performance of Your Web Application	Matt Odhner	http://www.microsoft.com/technet/iis/wastip.asp
Improve the Performance of Your MDAC Application	Suresh Kannan	http://www.microsoft.com/data/impperf.htm