Apache: The Definitive Guide, 3rd Edition

Profiling

The classic tool for making programs run faster is the profiler. It counts clock ticks as each line of code is executed by the processor. The total count for each line shows the time it took. The output is a log file that can be sorted by a presentation package to show up the lines that take most time to execute. Very often problems are revealed that you can’t do much about: processing has to be done, and it just takes time. However, occasionally the profiler shows you that the problem is caused by some subroutine being called unnecessarily often. You cut it out of the loop or reorganize the loop to work more efficiently, and your script leaps satisfyingly forward.

A Perl profiler, DProf, is available from CPAN (see http://search.cpan.org).There are two ways of using it (see the documentation). The better way is to put the following line in your Config file:

...
PerlModule Apache::DProf
...

This pulls in the profiler and creates a directory below <ServerRoot> called dprof/$$. In there you will find a file called tmon.out, which contains the results. You can study it by running the script dprofpp, which comes with the package.

Interesting as the results of a profiler are, it is not worth spending too much effort on them. If a part of the code accounts for 50% of the execution time (which is most unlikely), getting rid of it altogether will only double the speed of execution. Much more likely that a part of the code accounts for 10% of the time — and getting rid of it (supposing ...