There are many definitions of science. However, the most common definition is the systematic gathering and organization of knowledge. This refers to knowledge that, apart from its original purpose, can be used for further explorations of even more, and possibly further detailed, knowledge. Gaining new knowledge often involves validating theorems or ideas through experiments and tests. When a test has been validated or falsified, some things can be changed, or tuned, and the test can be performed again in order to gather more knowledge about what is going on in certain environments or situations.

As we will see, this approach of searching for knowledge in science is directly transferable to the improvement of performance in IT systems. In our opinion, performance testing and tuning is a science that is possibly spiced with some gut feeling (which is often based on experience, so we would say knowledge possibly sprung from science).

In this chapter, we will kick off by defining some key terminologies and measures of performance. After that, we will turn our focus to the process of performance tuning and its place in the software development process and the software life cycle. This will include its iterative behavior and talking about when, where, and how performance tuning should be done in an enterprise stack.