[rdoherty]

First thing I tell anyone when they say "this code is slow because of X" is to profile it. Profile, profile, profile! More often than not your assumptions are wrong.

There's a myriad of tools out there for profiling, some language specific, some not. Learn at least one of them well, how to read flamegraphs and how to benchmark properly (warmup code, synthetic vs real traffic, etc). There's definitely a jump between making guesses and hoping you improve performance vs truly understanding what your code is doing.

[ykevinator]

Second this, more often than not