Intended Audience
Introduction
The Caching Imperative
The Script Caching Solution
The Caching Script
Implementation: Avoiding Common Pitfalls
Summary
The Script
About the Author

Intended Audience
This article is intended for the PHP programmer interested in creating a static HTML cache of dynamic PHP scripts. The article has been written specifically for an Apache server running PHP scripts, but the ideas described here are applicable to almost any Web environment.

The article assumes that you have some experience with creating dynamic Web sites and that you are familiar with HTTP – at least enough to know what a "404 Page Not Found" error means and the definition of the environment variables $REQUEST_URI and $DOCUMENT_ROOT.

Introduction
The benefits to using dynamic Web pages are well known, but there are nonetheless two significant drawbacks: speed and search engine accessibility.

Speed: The speed in which a user receives a page after clicking a link or entering a URL is a crucial factor for a Website. It depends on dozens of variables, some of which you may have control over and some of which you don’t. There are countless bottlenecks in the process, and it’s probably impossible to fix them all. This bottleneck we will tackle here is the one caused by waiting for the server side scripts to create the HTML output.


Search Engine Accessibility: By this I mean the ability of search engines to point to a particular Web page. Most search engines function by using a "Crawler" program. Crawler programs begin on a certain page and navigate through the links on it. Every page a crawler visits is then indexed on the search engine’s database.
Most crawlers, however, are only programmed to navigate through static (HTML) pages – not dynamic ones. So, for example, pages with URLs that contain a "?" character (indicating a query string) or a filename ending with ".php" will not be accessed. Consequently, crawlers will not index these pages, making your site less accessible to new visitors.


Note: A crawler cannot tell the difference between an HTML file’s output and a PHP file’s. They both send the same content type. Therefore, most crawlers simply decide according to the filename and/or if there is a query string in the URL – that is, if the URL contains a "?".

This article discusses a procedure for dealing with both of these drawbacks. The article’s script should be sufficient for use under most circumstances – but in particular, small scale Web sites and individual script pages that are only moderately subject to change (dynamics).

The Caching Imperative
Simply speaking, caching entails storing the output of one or more dynamic scripts into static HTML files. A visitor to your site would be directed to these HTML files rather than to their original dynamic versions.

The mechanism for doing so can be described using a Magazine’s Web site as an example.

A Magazine’s Web site would likely have a database that contained numerous articles and stories. You would normally have a script (say "show_article.php") that:

Receives an article ID number
Reads the article’s content from the database
Puts it into some kind of HTML template
Formats the whole page with navigation links etc...
Sends the resulting HTML to the visitor’s browser
As such, in the site’s homepage you might have links to current articles coded as follows:

<a href="show_article.php?id=123">Cache Article</a>
Now, articles tend to be static and you would hope that the site was operating under heavy request loads (because it’s popular!!). Consequently, requests for each article would undergo extensive processing – meaning access database, search article, and display it.

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