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 point seem pretty daunting. Not only are we measuring something that's always changing in ways we don't understand, driven by factors we can't control, but our mere observation of the system induces further change in it! Why do we bother to measure, then? The answer is simple: without careful, methodical measurements, it becomes practically impossible to provide reasoned, analytical solutions to problems, because we don't understand why the problem exists or what happened . It's always better to know something about the situation. If we didn't strive to understand, we would be doomed to be Cargo Cult Systems Administrators, sitting at our desks with wooden keyboards and terminals, [1] waiting for the magicians to come back in their shiny silver birds at a few hundred dollars an hour to fix our problems for us. That's not a good solution for anyone but the magicians.

[1] Although I have often wished my pager or cellular phone was wooden, and therefore not able to ring.

In this chapter, I break workflow management into two distinct parts : workflow characterization and workflow control. It is important that they are presented in this order; control imposed haphazardly is a real mess, and many a consultant has made a small fortune cleaning up after it. Do not despair about the complexity implicit in this topic. There are many tools that can help us understand and, subsequently, restrict the loads placed on the systems we manage; many of them are minimally intrusive . I then move into benchmarks, as standardized ways of measuring the performance of various workloads on different systems. Consider this your primer on turning Cargo Cult wood into twenty-first century silicon.



System Performance Tuning2002
System Performance Tuning2002
ISBN: N/A
EAN: N/A
Year: 2004
Pages: 97

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