System Performance Tuning, 2nd Edition

Chapter 2. Workflow Management

The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa.

—Werner von Heisenberg, 1927

The topic of “workflow management” is slippery: it can be interpreted to mean many different things. In this chapter, I describe practical means to accomplish the zeroth principle of performance tuning: understanding the environment as it exists. This is the beating heart of dynamic performance tuning. The rest of this book exists simply to improve your understanding about possible environments.

We concern ourselves, as mentioned, primarily with dynamic performance analysis: the system we are measuring is changing beneath us. It is, in some sense, like watching a pond. There might be a creek that flows into the pond; how does that affect the life in the pond? What happens when some beavers build a dam across that creek, when some children find the pond and throw rocks into it, or when someone dumps the ashes of old love letters in the middle of it?

To further complicate things, we are governed by an inviolable principle of physics. Heisenberg’s Principle of Uncertainty says that no matter how carefully we try, we will always perturb the system when we measure it, and some piece of knowledge will remain outside of our grasp. We can minimize the perturbation, however, and throughout this chapter we’ll concern ourselves with how significant of a perturbation our measurements are inducing.

Things at this ...