Perl Cookbook, 2nd Edition

Chapter 21. mod_perl

Speed is good only when wisdom leads the way.

—James Poe

Introduction

The mod_perl project (http://perl.apache.org/) integrates Perl with the Apache web server. That way, you can use Perl to configure Apache, manipulate and respond to requests, write to log files, and much more.

Most people begin using mod_perl to avoid the performance penalty of CGI. With CGI programs, the web server starts a separate process for each request. This can be a costly business on most operating systems, with lots of kernel data structures to copy and file I/O to load the new process’s binary. If you serve a lot of requests, the operating system may be unable to keep up with the demand for new processes, leaving your web server (and indeed the whole machine) unresponsive.

By embedding the Perl interpreter within the Apache process, mod_perl removes the need to start a separate process to generate dynamic content. Indeed, the Apache::Registry and Apache::PerlRun modules provide a CGI environment within this persistent Perl interpreter (and form the basis of Recipe 21.12). This gives you an immediate performance boost over CGI (some report 10-100x performance) but doesn’t take full advantage of the integration of Perl with Apache. For that, you need to write your own handlers.

Handlers

Because Apache has access to Perl at every step as it processes a request (and vice versa), you can write code (handlers) for every phase of a request-response cycle. There are 13 phases for which you can ...