Hangers and Optimization

I’ve talked about context before. I know context is important. Even so, I still get reminded of its importance by the smallest of things. After just over 2 years I’m on a business trip again and something happened last night that reminded me again how important context is.

When I got to my room I went to hang up my shirts because I don’t want to have to iron them. When I went to hang them up some of the hangers were hung hook in and some were hung hook out. Which begs the question, hook in, hook out, or random?

Which gets right to the question of context and optimization. My father was a policeman. And a volunteer fireman. If you asked him how hangers should be arranged the answer you got would depend on which hat he was wearing. The fireman would say make them all be pointing the same way, preferably in. That would make it easier to grab lots of them at once and take them off the bar if you needed to move them in a hurry. The policeman, on the other hand, would say that you should hang them randomly. That will make it harder for someone to grab an bunch of them and run off. So which way you hang your clothes depends on what you’re trying to optimize for.

In engineering, software or otherwise, the answer is also often, it depends. There are lots of ways to meet the base requirements. Which one to choose depends on what you’re trying to optimize for. Are you optimizing for resource (memory, disk, CPU, network, etc.) usage? Maybe it’s throughput, or latency. It might be an one of those non-functional requirements, like reliability or uptime. Are you optimizing for time? Is the short term more important, or the long term? Or maybe it’s a business requirement. Minimizing cost in one area. Minimizing waste in a division. Maximizing revenue on a product.

Remember that regardless of what you’re optimizing for, there’s always something you’re giving up. Minimizing resource usage might increase latency or decrease throughput. What’s best for tomorrow might not be best for next week, next month, or next year. But there are times when you need to optimize for short term or there won’t be a long term to worry about. You can minimize development costs by not having any developers, but that’s really going to delay your release date.

The trick is to recognize that just because you’ve found a local maximum (or minimum), that doesn’t mean you’ve found the global maximum (minimum). Whether or not that’s the right answer depends.