Comparison
Pareto principlevsPremature optimisation
Pareto principle
a fifth of the features covered nearly all of the usage, and the rest of the roadmap was the other four fifths.
The observation that a small share of causes produces most of the effects. It is useful in prioritisation and in performance work — most latency is usually in a couple of places — and it is dangerous as an excuse, because the last twenty percent of a product is often the part that makes it usable at all. Treat it as a prompt to go and measure the distribution rather than as a licence to stop.
Full entry →Premature optimisation
you hand-rolled a cache for a function that turned out to run twice a day.
Making code faster and worse before knowing whether its speed was ever a problem. The full quotation matters and is usually dropped: Knuth's point was about the ninety-seven percent of small efficiencies, not about ignoring performance entirely. Used honestly it is an argument for measuring first; used lazily it becomes a way to dismiss any performance concern, which is why the more useful phrasing in a review is 'what does the profile say'.
Full entry →