Question

How is profiling different from logging?

Is it just that profiling is used for performance measurements to see how long each function takes? Or am I off?

Typically, how are profiling libraries used?

What types of stats are obtained by profiling?

Answer 1

Logging tells you what happened. It’s great for forensics and debugging.

Profiling quantifies that: it tells you how much time your code spent in each area, or how many times a body of code was executed. It helps you improve your code’s performance.

Profiling typically operates at the level of a line of code, a function call, or sometimes a file. For each level, it can typically tell you:

• How many times the unit was executed. It’s generally less important to optimize rarely-used code than code that executes millions of times. One exception is code that makes a user (or another process) wait for it to complete.

• How many times a branch was taken, say in an if or switch statement. Again, you typically care most about optimizing often-used code.

• How much time was spent in a particular function. Warning: even experienced developers are often surprised by these results. It’s very difficult to predict where your ‘time sinks’ are.

• How much time was spent in a function and all functions called within that function. Maybe it’s not the function itself, but its children, that need optimizing.

• How many times the unit was called by each caller. You may find that a particular function is called primarily from an unexpected place.

Armed with the data from a good profiler, you can often gain significant improvements in performance with relatively little effort.