Why is FastCGI fast? [closed]

Question

FastCGI provides a way to improve the performance of the thousands of Perl applications that have been written for the Web. -Source

and how does it do that?

Answer 1

Mark R. Brown's whitepaper on the subject claims that one of the primary benefits of FastCGI is that different requests can share a single cache, making caching practical:

Today's most widely deployed Web server APIs are based on a pool-of-processes server model. The Web server consists of a parent process and a pool of child processes. Processes do not share memory. An incoming request is assigned to an idle child at random. The child runs the request to completion before accepting a new request. A typical server has 32 child processes, a large server has 100 or 200.

In-memory caching works very poorly in this server model because processes do not share memory and incoming requests are assigned to processes at random. For instance, to keep a frequently-used file available in memory the server must keep a file copy per child, which wastes memory. When the file is modified all the children need to be notified, which is complex (the APIs don't provide a way to do it).

FastCGI is designed to allow effective in-memory caching. Requests are routed from any child process to a FastCGI application server. The FastCGI application process maintains an in-memory cache.

Answer 2

"Instead of creating a new process for each request, FastCGI uses persistent processes to handle a series of requests. These processes are owned by the FastCGI server, not the web server."

-- Wikipedia