How Tall is Your Ladder? Premature Optimization or Prudent Foundation?

by Louis Marascio on July 14, 2008

Premature optimization: it’s the hater-programmer’s trump card. These days it seems everywhere I look I see these folks yelling, “Stop, you’re optimizing prematurely! Thou shalt perish in programmer hell!” To this I always want to respond, “What exactly is premature optimization, and why do you think I’m doing it?”

It’s funny, really. In the past six months I’ve heard premature optimization thrown about as a reason not to do something at least seven times. So often has it been used, in such dubious circumstances, that I’ve come to realize that the original intent behind this nugget of wisdom has been warped and skewed by hater-programmers with dubious intentions.

According to the ever growing awareness, Wikipedia, Donald Knuth stated the following in the article “Structured Programming with go to Statements” in the ACM Journal Computing Surveys:

We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.

The article on Wikipedia goes on to say:

“Premature optimization” is a phrase used to describe a situation where a programmer lets performance considerations affect the design of a piece of code. This can result in a design that is not as clean as it could have been or code that is incorrect, because the code is complicated by the optimization and the programmer is distracted by optimizing.

This I completely agree with. Premature optimization is, essentially, a way to say that programmers would rather fiddle bits than confront the design of their software critically. I’d even provide an alternate, perhaps more accurate description: premature optimization is optimization without profiling. In other words, you’re optimizing without pinpointing the problem and without the ability to measure the results; however, this doesn’t mean you have to make simplistic choices when faced with a lack of data.

In my opinion this is one of the most commonly misused tenants of computer science today. So often is “premature optimization” used as an argument against proposed solutions, that I have begun to seriously question the rationale and motives behind most people who propose it as a counter-argument in technical debates. I simply think it is grossly mis-applied. Even more annoying is when people actually suggest that language choice is a premature optimization.

Let me provide a metaphor. Suppose you were asked to fetch a ladder for your friend. Now, you’re into ladders. Ladders are definitely your thing. You have three ladders, each a different size: a step ladder, a fixed ladder, and an extension ladder. Each one has its intended uses, and each one has explicit weaknesses. Which one do you take? You can only pick one.

If you’re a premature-optimization-acolyte you pick the step ladder. Why? Well anything else would simply be overcomplicating the situation without sufficient reason not to. The step ladder is small, easy to transport, and most importantly, sort of cute.

Me? Well, I’m no acolyte. Here is how I see it.

The step ladder is basically useless. It fills a very specific need, but is not adaptable beyond that need. It’s useful in that you can reach items slightly above your head, but its primary utility comes from the fact that the step ladder itself can neatly be tucked away, forgotten, behind some counter or under a bed somewhere. Height, my friend, is not its strength.

So, is it the fixed ladder or the extension ladder? Well, that’s easy depending on the answer to the following question: is the fixed ladder of the over-the-top, uber-Little Giant variety? If yes, then pick the fixed ladder and move on. If no, then the extension ladder is my choice.

Did you hear that? That was several thousand hater-programmers around the world gasping all at once. This is what they’re saying and thinking: “You’ve just prematurely optimized the solution. There was no data to prove that you needed a ladder that could extend to 42 feet.” Bah!

Humans, especially programmers, like to latch on to things we believe we understand. This precept of truth from Dr. Knuth is one of those things. Premature optimization is bad, but inappropriate application of the precept of premature optimization is, IMO, much worse. Why? It suppresses good ideas and creative thinking.

The ladder example provided above is straightforward. A ladder is about height. When asked to choose a ladder without sufficient data as to the height of the area to be reached pick a ladder that provides, in this order, the most flexibility and the most height. If the ladder is a Little Giant then pick it, that thing is amazing, 24 ladders in one! Otherwise, pick the ladder that provides the most height, they can almost always be positioned to reach a lower point, but can very, very rarely (at least safely) be positioned to reach a point above the maximum height of the ladder plus the height of the individual.

How does this apply to software? Well, more often than not, technology, tool, or design choices are changed because the argument against premature optimization is used to argue against what was simply a decision to favor flexibility, or as I call it, a Prudent Foundation.

Prudent foundations are simple. Given everything you know about a problem, pick something that your gut says is flexible and good enough, but nothing more. Be concious of sacrificing flexibility, that’s how we get out of binds later on. The biggest risk we face as engineers is the risk of the unknown. Picking a prudent foundation, or a solution that minimizes the risk of the unknown, is the best we can do given the circumstances we are faced with.

Let’s examine the most egregious misapplication of premature optimization. As I stated earlier I believe this to be language choice. Choosing a programming language is almost never a premature optimization. Language choice is about many other things, but mostly it’s about picking the right tool for the job given the problem’s business context. Optimization, premature or otherwise, plays very little role here. The problem and business context define the criteria under which you should consider your decision.

Picking a prudent foundation is not premature optimization, even if 10,000 hater-programmers believe it be at first glance. Usually, the premature optimization crowd are speaking from a position of comfort. It is premature optimization if it uses anything they aren’t: (a) familiar with, or (b) comfortable with (no, these are not the same thing).

As engineers, one of the most important things we should be doing is discovering and promoting the prudent foundation for the problems we are faced with by making sound technology decisions.

  1. We all know them. These are the people who argue viewpoints based on religion. They are usually arguing against pragmatic solutions and are most commonly found aligned with the forces of evil.
  2. That’s right, I get to provide my own, personal, humble, opinions on my very own website. Go figure.

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