How to Make Things Faster

Chapter 81. Be Careful What You Wish For

Sometimes, you just need to take a walk with your customer and talk through what you’re really trying to accomplish. One time, on one such walk, I asked an IT director with a slow system what he really hoped to achieve from my consulting visit. He said, “To be honest with you, what I really want is to have my CPUs be at least 40% idle during my peak-load hour every afternoon.”

I told him I understood what he meant, but that lower CPU utilization wasn’t really what he wanted. Of course, this was a plot twist for him. Why would that not be what he really wanted?

I explained that it’s the wrong goal, because there are ways I could give him what he’s asking for, without giving him anything that he actually wants. For instance, I asked him if he had any slow, really old disk drives in a storage closet somewhere. I said that if we could install those really slow disk drives, it would reduce his CPU utilization, which would meet his stated goal, but it wouldn’t give him what he really wanted.

You always risk wasting your time if you don’t look at the right “it.”

The following sequence diagram shows why. Slower disks would cause more CPU idle time, which would officially fulfill his wish. But it would come at the expense of making his programs take longer, which is counter to what he really wants.

With slow enough drives (paper tape, anyone?!), ...