16.1: What Does Profiling Mean?

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Profiling an application is a term commonly employed that refers to obtaining dynamic information from a controlled program execution. The obtained information is intended to provide important hints on how to improve the program execution. These hints are usually numerical measurements, easily comparable from one program execution to another.

In this chapter, we will consider measurement related to method execution time and memory consumption. Note that other kind of information may be extracted from a program execution, in particular the method call graph.

It is interesting to observe that a program execution usually follows the universal 80-20 rule: only a few amount of the total amount of methods (let’s say 20%) consume the largest part of the available resources (80% of memory and CPU consumption). Optimizing an application is essentially a matter of tradeoff therefore. In this chapter we will see how to use the available tools to quickly identify these 20% of methods and how to measure the progress coming along the program enhancements we bring.

Experience shows that having unit tests is essential to ensure that we do not break the program semantics when optimizing it. When replacing an algorithm by another, we ought to make sure that the program still do what it is supposed to do.