Modeling the Real World for Load Testing Web Sites

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do not want graphics or applets downloaded, Web site visitors will not only speed up the delivery of a Web page that contains these files, but will also consume a smaller portion of the Web site's bandwidth and fewer Web server connections. If present in significant numbers, these clients can have a noticeable effect upon the performance of the Web site.

7. Client Internet Access Speeds
The transmission speed or bandwidth that your Web application will use can have a significant impact on the overall design, implementation, and testing of your Web site. In the early days of the Web (circa mid-1990s), 14.4 Kbps was the most common (e.g., standard) communications speed available. Hence, 14.4 Kbps became the lowest common denominator for Internet access. When 28.8 Kbps modems were introduced, however, they offered a significant performance improvement over 14.4 Kbps modems and quickly surpassed 14.4 Kbps modems in popularity. When 56.6 Kbps modems were introduced, the performance improvement wasn't as significant. Consequently, 28.8 Kbps are still in use and unlike the 14.4 Kbps (which has nearly vanished) still comprise a significant (although decreasing) proportion of the Internet population. Many companies therefore use the 28.8 Kbps transmission speed when specifying the performance requirements of their Web site.

8. Background Noise
Unless the production servers and network are going to be dedicated to supporting the Web site, you should ensure that the servers and network in the system test environment are loaded with appropriate background tasks. When designing a load to test the performance of a Web site or application, consider what additional activities need to be added to a test environment to accurately reflect the performance degradation caused by "background noise." Background noise is created by other applications running that will also be running on the production servers once the application under test moves into production, and other network traffic that will consume network bandwidth and possibly increase the collision rate of the data packets being transmitted over the LAN and/or WAN.

9. User Geographic Locations
Due to network topologies, response times for Web sites vary around the country and around the world. Internet response times can vary from city to city depending on the time of day, the geographic distance between the client and the host Web site, and the local network capacities at the client-side. Remote performance testing can become particularly important if mirror sites are to be strategically positioned in order to improve response times for distant locations.

But how can you effectively test the performance of your Web site from locations that are thousands of miles away? Possible solutions include

  • using the services of a third-party company that specializes in testing a Web site from different locations around the world
  • utilizing the different physical locations (branches) that your organization may already possess, coordinating the execution of your test plan with coworkers at the offices
  • using a modem to dial ISP telephone numbers in different cities and factoring out the additional time for the cross-country modem connection
  • buy an "around the world" airplane ticket for one or more of the Web site's testers

Getting the Right Mix
When developing the load profile that will be used for performance testing, try to take into account as many of the previously mentioned parameters as possible. While a single parameter may only affect the test results by a few percent, the accumulation of several parameters may add up and have a significant impact on the test results.

Credit
This article is drawn from The Web Testing Handbook by Steve Splaine and Stefan Jaskiel and from SQE's Web Performance & Security Testing

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About the author

Steve Splaine's picture Steve Splaine

Steven Splaine is a chartered software engineer with more than twenty years of experience in developing software systems: Web/Internet, client/server, mainframe, and PCs. He is an experienced project manager, tester, developer, and presenter, who has consulted with more than one hundred companies in North America and Europe. In addition, Steven is a regular speaker at software testing conferences, lead author of The Web Testing Handbook and Testing Web Security, and an advisor/consultant to several Web testing tool vendors and investors.

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