How to Make Things Faster

Chapter 52. Efficiency

Efficiency is getting the output you want for the least possible investment of input. It is an inverse measure of waste. Efficiency is how you flourish on a budget. To a performance analyst, eliminating waste—to get more from less—should feel like a genetic imperative.

An efficient program is one that produces correct and useful output with the least possible amount of work. The trial balance report that Martha disabled was inefficient by its mere existence: it didn’t matter how efficient its code was or wasn’t, the trial balance reports were wasteful because they weren’t useful. Kevin’s invoicing program, though both correct and useful, was inefficient due to a data access algorithm that did more work than necessary.

An efficient system is a system that executes only programs that are necessary and efficient. Do you notice how it always comes back to the thing the user experiences—the thing you’re supposed to be looking at? It’s no coincidence. Performance matters where the user is. Thus, it’s important to know how to measure the efficiency of your programs. With profiles, it’s easy. A program is efficient if and only if:

• It produces correct and useful output; and

• It executes no unnecessary events (calls, instructions, etc.).

Just to be clear, when I say “a program” (or “it”), I mean all the code your program executes or causes to be executed, including its own code and all of the subroutines it executes, including both user library calls and system ...