It is conceivable that a really good machine can learn our hash algorithm really well, but in the case of string hashing we still have to walk some memory to give us reasonable assurance of unique hash codes. So there’s performance sin #1 violated: never read from memory.

Avoiding Hash Lookups in a Ruby Implementation, on the quest to eliminate the use of ad-hoc hashes inside JRuby. I love that the cardinal sin of a runtime is to avoid memory reads. It makes avoiding random database lookups in web applications look like a walk in the park.

On the other hand, consider how much fun it is to write compilers; their cardinal sin is to avoid conditionals or anything that would stall the processor pipeline. If that seems pedestrian, then consider the cardinal sin of a processor designer: don’t do anything that will take longer than one clock cycle, or half a billionth of a second if you’re keeping score at home.