What are the absolute and relative costs of different operations in PHP?

Question

I'm looking for a elaborate list comparing different operations in PHP. For example: echo vs. printf, ++$i vs $i++, a direct function call vs. object function call, array access vs. direct data access, global vs. local variables, mysql_fetch_assoc vs. mysql_fetch_row etc. Of course these figures probably highly depend on the used version, the OS, hardware and many other factors, but I saw lists like this for c/c++ and maybe there is something similar for PHP.

Update

Will leave this question open for two more days. Maybe we can get a few more of these usefull links!

Answer 1

Perhaps this can help you with some of the functions/operators: http://www.phpbench.com/

Answer 2

why not run a few tests yourself comparing them? That way you know that for a machine with X specs runs echo at Y time whilst it does printf at Z time?

Answer 3

"The First Rule of Program Optimization: Don't do it. The Second Rule of Program Optimization (for experts only!): Don't do it yet."- Michael A. Jackson

Answer 4

“We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil." Donald Knuth.

The thing I like the most about this statement: Note that he says "small efficiencies". He's talking about code tuning... Essentially, I think he's arguing for getting your algorithm right from the beginning, but saving the code tuning for only when it's absolutely necessary.

Answer 5

Be careful! Some days ago, this article at google code appeared on just this subject. It was refuted almost immediately by this refutation. So watch out and test everytime.