Stress Testing

Stress testing is performed to evaluate the behaviour of a web application when it is subjected to loads beyond its operational limits. In other words, the purpose of stress testing is to see how the system handles an amount of traffic beyond what it is designed for. For such kind of test, the web-based system is simulated with a heavy load than expectations. Its very helpful to evaluate the resutls of an unexpected heavy internet traffic. The purpose of stress testing is to identify breakpoints and bottlenecks in the system, so that the system can be tuned, upgraded and durable (Zwanzinger, 2004). Stress testing provides a measurement of throughput, application response time, and resource utilization at levels further than the initial loads. Stress testing also makes it possible for Performance and Capacity Management teams to identify if there is any need of additional resources or corrective action which must be taken in order to meet future business growth demands.

Load Testing

For web-based systems, Load testing is useful for figuring out how much capacity a web-based system can handle, but it is more important for identifying bottlenecks that occur only under heavy load. The goal of load testing is to simulate real-world usage to find out whether the web-based system can maintain the requested number of users with acceptable response times. We can define this load in terms of concurrent users or HTTP connections trying to accecss the web system. It is considered to be very useful to test the web-based system to its limits by saturating it with a large amount of transactions, users, and data. It’s very helpful to know that how the web application will respond in the real life. According to Kumar, “Load Testing is creation of a simulated load on a real computer system by using virtual users who submit work as real users would do at real client workstations and thus testing the systems ability to support such workload” (Kumar, 2001). To simulate real users, scripts are created that combine together many common user actions into virtual sessions. Bottlenecks in the system will usually become apparent during this type of test. Load testing is also performed with single operations, or use cases, in order to locate performance issues with specific components under load.

Load testing is performed incrementally, with a fixed number of users added per increment. As users are added, the response time and resource utilization values will increase (Mercury, 2006). Obtaining these performance measures helps facilitate planning for future needs. Also, analysis may indicate that the system needs to be scaled in order to accommodate defined performance requirements.

The problem with load testing is to define the load requirements. It is possible to predict a workload in intranets, because they have usually finite and known users. However, with internets, it is very hard to predict how many users can access and load a web system. Mostly calculations are based on word of mouth recommendations, success of marketing campaigns, and in many cases, luck (Hower, 2006).

Web-based Systems Architecture

Where the web-based systems have increased the number of users, there number of risks has also been increased. So, application performance needs greater attention. In online survey in USA, it has been found that an average waiting time of a web user is eight seconds for downloading a complete page before leaving the site. In France, there may be some variation in this limit but to provide high performance is a main issue in the success of a web system (Cassone, 2001).

A web-based system is different from client-server application i.e. users and customers don’t have much knowledge, its architecture (Proxies, DNS, Servers, firewalls etc.) is more complex, and there are more risks. A web-based system can be consisted of a variety of components, like web servers, databases, and application servers, as well as network devices such as firewalls, routers, switches and load balancers (Dustin, 2002). The range of complexity in web-based systems varies from simple websites to large web systems like Yahoo, Google, or Amazon which includes complex search engines and order completion. We can see the architecture of web-based system in this way, if we take the model of a traditional business transaction system and to change the customer front end by the website. A customer purchases the company products or any kind of services, in exchange for money. There are methods that make it possible that transaction among customer and company. As a substitute of a sales representative, a cashier, a clerk, or such person, the browser will make it possible to point that website. This will result that company will never be closed. Customers can purchase their selves.

For example think about a vending machine. It has a basic user interface. The key function of the machine is to fill orders on the basis of input from users and it also authenticates transfer of funds. Now let’s add some complexity into the machine. We make User Interface a browser-based solution in place of touch pad, which is required to run in different browsers on different operating systems. And machine will have capability to fulfil orders directly from a warehouse, whilst re-stocking and tracking inventory. As a result, people don’t need to put coins in the machine, but they will enter their credit card information. When the people will make transactions, the machine will be required a real time access to credit companies in order to approve these transactions. Furthermore, we would also be expecting that all credit card information that we enter should be really secure. (Macintosh, 2000)

Performance has been a driving force in system architecture for quite a while. Since application performance greatly depends on the architecture, and it is considered to be vital, “as the price/performance ratio of hardware plummets and the cost of developing software rises, other qualities have emerged as important competitors to performance” (Bass, 2003). To test and measure performance of web-based systems efficiently, and to identify what possible enhancements could be there, it’s relatively important to describe its architecture.