In this chapter, we looked at some real cases that the author encountered in his work. Was it only a mere listing of some unrelated cases or did we learn something from them?
For me, the recurrent theme in each of these cases was how unexpected these problems were. Some quite reasonable assumptions were made, the software was written, but then it turned out that, despite the whole reasoning there were performance problems showing up! So, one of the lessons from these problem cases is that you'll never be sure until you've comprehensively tested your system.
The other surprise is how often the underlying reason is very simple, but not exactly trivial. This includes situations where you have a poorly scaling data structure, a linear or a quadratic algorithm, or a bad locking strategy. However, this is also encouraging – once we are able to determine the...