97 Things Every Programmer Should Know

Chapter 46. Know Your Limits

Greg Colvin

Man’s got to know his limitations.

—Dirty Harry

YOUR RESOURCES ARE LIMITED. You only have so much time and money to do your work, including the time and money needed to keep your knowledge, skills, and tools up to date. You can only work so hard, so fast, so smart, and so long. Your tools are only so powerful. Your target machines are only so powerful. So you have to respect the limits of your resources.

How to respect those limits? Know yourself, know your people, know your budgets, and know your stuff. Especially, as a software engineer, know the space and time complexity of your data structures and algorithms, and the architecture and performance characteristics of your systems. Your job is to create an optimal marriage of software and systems.

Space and time complexity are given as the function O(f(n)), which for n equal the size of the input is the asymptotic space or time required as n grows to infinity. Important complexity classes for f(n) include ln(n), n, n ln(n), n^e, and eⁿ. As graphing these functions clearly shows, as n gets bigger, O(ln(n)) is ever so much smaller than O(n) and O(n ln(n)), which are ever so much smaller than O(n^e) and O(eⁿ). As Sean Parent puts it, for achievable n, all complexity classes amount to near-constant, near-linear, or near-infinite.

Complexity analysis is measured in terms of an abstract machine, but ...