10. Improving Performance

In many ways, performance is at odds with maintainability and portability. To achieve improved speed or memory usage, the most clear algorithm sometimes gives way to confusing code. To exploit special purpose hardware or operating system services, non-portable implementation dependencies are introduced. When concerned about performance, you must decide how well each algorithm meets its performance and maintainability goals. Use the guidelines in this chapter with care; they may be hazardous to your software.

The best way to build a system that satisfies its performance requirements is through good design. You should not assume that speeding up your code will result in a visible increase in system execution. In most applications, the overall throughput of the system is not defined by the execution speed of the code but by the interaction between concurrent processes and the response time of the system peripherals.

Most of the guidelines in this chapter read "... when measured performance indicates." "Indicates" means that you have determined that the benefit in increased performance to your application in your environment outweighs the negative side effects on understandability, maintainability, and portability of the resulting code. Many of the guideline examples show the alternatives that you will need to measure in order to determine if the guideline is indicated.