Before we can discuss how to improve performance, it's necessary to define what performance is. This isn't as simple as it sounds-people often mean very different things when they talk about performance. There are several aspects of performance, each of which contribute to the overall performance of an application.

Computers fascinate people with their ability to carry out tasks with blinding speed. When a computer, for whatever reason, doesn't perform a task quickly, users are disappointed. Developers often use the terms "speed" and "performance" interchangeably. However, to understand the different types of problems that can be encountered, all of the different aspects of performance must be considered:

• Computational performance
• RAM footprint
• Startup time
• Scalability
• Perceived performance

These factors lay the foundation for a better understanding of the performance landscape. Some aspects of performance are primarily applicable to client-side systems, some to server-side systems, and some to both. Understanding how each factor can contribute to the performance characteristics of a system will help you analyze the performance of your own applications.

1.1 Computational Performance

Computational performance is what most people think about first when discussing software performance. Computational performance concerns characteristics such as

• How many instructions are required to execute a statement?
• How much overhead does a particular virtual method call incur?
• Should I use a quick-sort or a bubble-sort here?

Much of the software performance literature centers on computational performance. Obviously, which algorithms you use and how you implement them are key factors in the overall performance of your software - focuses on the selection and use of algorithms and data structures. It turns out, however, that this is only part of the performance picture. You need to consider factors beyond computational performance if you want to produce truly high-performance software

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