Start Your Coding

Our mod_perl Apache server is ready to serve. That's the good news. But, like any high performance piece of machinery, mod_perl is not going to provide its optimum benefits right out of the box like this. Before you're ready to tweak and tune, however, it's important to get used to developing scripts in the mod_perl environment (and for better or worse, there is a lot of tweaking and tuning that can be done under the hood). Of course, you'll want to save your Perl scripts to the system directory aliased to /cgi-perl/ or whatever name you chose. Whether you are adapting existing scripts or writing anew, your Perl should interact with the browser just as you did before, via the CGI.pm module, which we looked at way back in Part 2 of the Perl You Need to Know. You can retrieve parameters and send output to the browser just as before, but keep in mind that although we continue to use the label "CGI" as a manner of speaking, scripts executed by mod_perl are not technically using the CGI extension.

Although many Perl scripts will run as-is in the mod_perl environment, you are not yet taking full advantage of mod_perl's benefits. We'll close out this month's installment looking at pre-loading Perl modules. Next month we'll look some more at optimizations, and also at some thorny pitfalls in coding practice that could undermine Perl scripts that otherwise work fine outside of mod_perl.

Your Perl scripts most probably begin by linking in some modules via the use() statement. At the least, you probably:

#!/usr/bin/perl
use CGI;

Because your script invocations will likely keep using many of the same modules, one mod_perl optimization is to pre-load these modules, allowing mod_perl to compile them once and keep them resident in memory. Future script executions do not then need to recompile these modules, shaving a few more milliseconds off total execution time. The typical way you can pre-load Perl modules is with the PerlModule directive, which you can place in Apache's httpd.conf file along with your other mod_perl directives:

Alias /cgi-perl/ 
"/usr/local/apache/cgi-perl/"
PerlModule CGI
<Location /cgi-perl>
SetHandler perl-script
PerlHandler Apache::Registry
Options ExecCGI
PerlSendHeader On
</Location>

You can list any other Perl modules you wish to pre-load in the one PerlModule directive, simply separated by spaces. There is a slightly more sophisticated method of pre-loading modules that involves using the PerlRequire directive to load a short script that contains "use ()" statements for each module -- this is not a necessary step to begin with, but is nicely illustrated in Vivek Khera's mod_perl_tuning document.

Just because you've pre-loaded a Perl module does not mean that you forego the "use ()" statement in your Perl script. Leave those in as they are. Perl will not waste time recompiling the module sources, but it will import necessary elements of the module into your script's namespace, allowing you to leave calls to the module unchanged in syntax within your script.

Basic Configuration
The Perl You Need to Know
Take Home Message: Optimizations