Performance and Profiling

Part of the Go course

At some point someone says the service is slow, and you open the code and immediately spot the loop that must be responsible. You rewrite it, it is much cleverer now, and the service is exactly as slow as before, because the actual cost was in a JSON encode three functions away that nobody thought about.

This happens to everyone, repeatedly, and it is not a failure of skill. Programs spend their time in places human intuition is bad at predicting, because the compiler, the garbage collector, and the CPU's caches are all making decisions you did not write. The only reliable way through is to measure, change one thing, and measure again. ...