The importance of load and stress testing of Web sites and applications

The importance of load and stress testing of Web sites and applications

By: Susan Dorfman , from ; developersnetwork.com

Businesses everywhere are launching internal and customer-focused applications on the World Wide Web, using them as channels to reach scores of employees and customers in a matter of seconds.

To assure the “immediacy” of the Internet, Web sites and Web-based applications must demonstrate proven speed (performance), quality, and scalability. As such, companies must test and measure how fast Web-system components work together so they can determine what kind of workload their Web servers can withstand, how many simultaneous hits the Web site can handle, how scalable their applications and hardware are, and how this affects quality and performance. This “load” testing process must be implemented during and after development, as it is incredibly important to test sites and applications under heavy loads. This will measure slow access, or site failure due to hardware limitations.

Gaining accurate information about Web-based application performance, to understand and manage the limits of any application within its given environment - is paramount to the successful development, deployment, management and growth of strategic business applications and sites, as well as the companies that deploy them.

What is Load Testing?

A load test simulates user activity and analyzes the effect of the real-world user environment on an application. By load testing a Web application throughout development, a company can identify problematic parts of a Web application before it is accessed by hundreds or thousands of users.

Load testing can offer proof that an important intranet or Internet application will work properly, and not produce work interruptions or unacceptable performance.

In almost all cases, load testing uncovers fatal errors that likely would have led to a system crash had deployment proceeded without testing.

Why is load testing important?

Load testing assists companies with the following:

Increase uptime of mission-critical Internet systems. Load testing increases the uptime of your mission-critical systems by helping you spot bottlenecks in your systems under large user stress scenarios before they happen in a production environment.

Avoid project failures by predicting site behavior under large user loads. It is a shame when so much effort is put into building a Web project only to realize that it won't scale after it has been deployed. Avoid project failures due to not testing high-load scenarios.

Measure and monitor performance of your e-business infrastructure. Watch your system handle (or not handle) the load of thousands of concurrent users hitting your site before you deploy and launch it for all the world to visit.

Protect IT investments by predicting scalability and performance. IT projects are expensive. The hardware, the staffing, the consultants, the bandwidth, and more add up quickly. Avoid wasting money on expensive IT resources and ensure that it will all scale with load testing.

By simultaneously simulating multiple users, load testing first determines whether an application can support its intended workload of customers and/or employees.

Simulating hundreds or thousands of users, load testing creates scripts that represent actual users and their daily, often disparate, operations. With a recorder (capture agent), load testing records user activities — including keystrokes, mouse movements, and HTTP requests — to create simulation scripts. Then, it plays back a mix of scripts representing a set of real users.

Load testing also charts the time a visitor to the site has to wait for browser responses. It finds hidden bugs and bottlenecks and gives developers the chance to correct them before the site goes into production. All hardware, software, and database vendors boast of the speed of their products, but load testing discloses how fast those products work within a unique environment, for primary transactions, during peak business hours.

Furthermore, load testing checks and maintains applications as their workloads increase, so systems can be adjusted accordingly. As businesses grow and change, it is important to confirm a Web site's ability to sustain growth. Developers can reuse scripts to alter usage levels, transaction mixes and rates, and application complexity. Load testing is the only way to verify the scalability of components working together.

What kind of problems could show up?

Most problems have to do with the bottlenecks that arise when different users depend on one common resource. For example, if your site depends on a single, common database, then the speed of data access could become an issue if your database queries are not efficient. Incorrect use of multithreading in Web server software can be another problem. Excessive disk access or memory leaks may also cause problems.

By identifying these problems early on, Web developers, designers and implementers can rewrite software, reconfigure hardware, or employ caching strategies to get order-of-magnitude performance increases.

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