FastCGI is a web server extension that allows you to convert CGI programs into persistent, long-lived server-like applications. The web server spawns a FastCGI process for each specified CGI application at startup, and these processes respond to requests, until they are explicitly terminated. If you expect a certain application to be used more than others, you can also ask FastCGI to spawn multiple processes to handle concurrent requests.

There are several advantages to this approach. A typical Perl CGI application has startup overhead for each request that includes the process of spawning a process and interpreting the code. And, if the code has a lengthy initialization process, that simply adds to the overhead. A typical FastCGI application does not suffer from any of these problems. There is no extra spawning for each request, and all the initialization is done at startup. Since these applications are long-lived, they allow you to store data between requests, which is also an advantage.