Assume a software product has three modules: A, B, and C. The software was running slow; no one seemed to know why. So, the development manager decided it was time to instrument the code. As shown in Figure 2-1, the developers inserted simple timers into each module. When the module began, a starting time was gathered; upon exit, the finish time was gathered.

Figure 2-1. Simple instrumentation example. Each product's modules have a simple start and stop timer, providing the ability to determine the module run time.

The development manager then repeatedly ran the product while the timers were recording module start and stop times. After he was satisfied that enough runs had occurred, he ran the query shown in Figure 2-2, and got the results shown in that figure.