mod_perl is one approach to overcome the performance penalty of serving dynamic pages using the CGI interface.

mod_perl creates a persistent Perl environment inside of the Apache web server. This means that Perl, your scripts and your modules run inside the web server itself. No external processes, loading and compiling of scripts and modules only once. Since mod_perl is so tightly integrated with Apache, you do not have to work exclusively with the CGI interface, you can also access internal Apache interfaces and data structures, allowing you to do much more than just handling page requests (such as URL rewriting, site authentication or custom logging).

Because of the memory requests and integration with the web server, mod_perl is offered by few hosting companies. However, if you project is big enough to need the performance enhancements of mod_perl, having your own server may make sense anyway (if not, Fast CGI might be an alternative to consider).

See also:

• http://perl.apache.org has a lot of great documentation
• Basics of CGI to Apache::Registry conversion for mod_perl 2.0
• Basics of CGI to Apache::Registry conversion for mod_perl 1.0
• Site Performance