Premature optimization is about delaying solving problems, not about performance

Premature optimization is the root of all evil - Donald Knuth

This is a phrase you hear a lot as a software engineer. I would claim it’s slightly misunderstood.

It’s usually understood to mean spending time on performance is not worth it until you understand why your software is slow, when in reality I think the useful message is don’t try and solve problems that don’t exist yet.

This is to say that the phrase is not really about performance but is about resisting the temptation to solve pre-empted problems. Instead of doing this, you should solve the problems at hand. When (or if) the problem you pre-empted arises, that is the time to solve it. Performance is a great example of this. You should wait until you a) have reason to spend time making your software faster and b) know why your software is slow. Only then should you invest the time & inflict the architectural damage to make your software faster.

Of course, taken to the extreme, this would lead us to some awful tech debt1. As with all one sentence pieces of advice this should be taken with a grain of salt. We should expand this a little bit – of course there are problems that we should solve up front. For example, it’s worth spending time on the architecture of your software before it grows to a size where you realize any of the benefits.

How are these “worth it” problems different from the kinds of problems that aren’t worth it? I’m honestly not sure – but problems that arise from irreversible decisions (like the architecture of your software) are problems that are worth trying to solve up front.

With all that in mind, here’s the updated but far less snappy “saying”:

To decide if a problem is worth solving prematurely (that is, before the problem has arisen), first consider: 1) the cost of solving the problem now 2) the cost of solving the problem at the time it would arise 3) the size of the fallout if the problem is not solved

cost now cost later potential fallout solve when?
low high high now
low low high later
any any low never?

This leaves room for “premature optimizations” that may become existential risks, or cheap architectural decisions early on that will save a lot of problems further down the line. An example of this is using a library like react to ship a simple MVP, because you know a) it does not add that much overhead at the start and b) will make it much easier to scale up the product later.

  1. having said that, I would wager that a team that only solved short term problems would outperform a team that strived for perfection up front.↩︎