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Thursday, October 21, 2010

Validation phase - System Testing - Performance Testing - Throughput

Throughput refers to the number of client requests processed within a certain unit of time. Typically, the unit of measurement is requests per second or pages per second. From a marketing perspective, throughput may also be measured in terms of visitors per day or page views per day, although smaller time units are more useful for performance testing because applications typically see peak loads of several times the average load in a day.

The throughput of the web site is often measured and analyzed at different stages of the design, develop, and deploy cycle. For example, in the process of capacity planning, throughput is one of the key parameters for determining the hardware and system requirements of a web site. Throughput also plays an important role in identifying performance bottlenecks and improving application and system performance. Whether a web farm uses a single server or multiple servers, throughput statistics show similar characteristics in reactions to various user load levels.

The throughput of a typical web site increases proportionally at the initial stages of increasing load. However, due to the limited system resources, throughput cannot be increased indefinitely. It will eventually reach a peak, and the overall performance of the site will start degrading with increased load. Maximum throughput is the maximum number of user requests that can be supported concurrently by the site in the given unit of time. The value of maximum throughput varies from site to site. It mainly depends on the complexity of the application. As with any statistic, throughput metrics can be manipulated by selectively ignoring some of the data.

In many ways, throughput and response time are related, as different approaches to thinking about the same problem. In general, sites with high latency will have low throughput. If you want to improve your throughput, you should analyze the same criteria as you would to reduce latency. Also, measurement of throughput without consideration of latency is misleading because latency often rises under load before throughput peaks. This means that peak throughput may occur at a latency that is unacceptable from an application usability standalone.

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