This entire site, like many, is built in PHP. PHP provides the power to simply 'pull' content from an external source, in the case of my site this is flat files but it could just as easily be an MySQL database or an XML file etc..

PHP Caching to Speed up Dynamically Generated Sites

PHP provides the power to simply 'pull' content from an external source, in the case of my site this is flat files but it could just as easily be an MySQL database or an XML file etc..

The downside to this is processing time, each request for one page can trigger multiple database queries, processing of the output, and formatting it for display... This can be quite slow on complex sites (or slower servers)

Ironically, these so-called 'dynamic' sites probably have very little changing content, this page will almost never be updated after the day it is written - yet each time someone requests it the scripts goes and fetches the content, applies various functions and filters to it, then outputs it to you...

Enter Caching
This is where caching can help us out, instead of regenerating the page every time, the scripts running this site generate it the first time they're asked to, then store a copy of what they send back to your browser. The next time a visitor requests the same page, the script will know it'd already generated one recently, and simply send that to the browser without all the hassle of re-running database queries or searches.

An Illustration
This example shows a request for a "News" page on a website, the News changes daily so it makes sense to have it in a database rather than as a static file so it can be easily updated and searched, The News page is a PHP script which does the following;

• Connect to an MySQL Database
• Request 5 most recent news items
• Sort news items from most recent to oldest
• Read a template file and substitute variables for content
• Output the finished page to the user

<?php
    ob_start(); // start the output buffer
?>

.. Your usual PHP script and HTML here ...

<?php
     $cachefile = "cache/home.html";
     $fp = fopen($cachefile, 'w'); // open the cache file "cache/home.html" for writing
     fwrite($fp, ob_get_contents()); // save the contents of output buffer to the file
     fclose($fp); // close the file
     ob_end_flush(); // Send the output to the browser
?>

<?php
$cachefile = "cache/home.html";
if (file_exists($cachefile)) {
// the page has been cached from an earlier request
include($cachefile); // output the contents of the cache file
exit; // exit the script, so that the rest isnt executed
}
?>

<?php
  $cachetime = 5 * 60; // 5 minutes
   // Serve from the cache if it is younger than $cachetime
   if (file_exists($cachefile) && (time() - $cachetime < filemtime($cachefile))) {
     include($cachefile);
     echo "<!-- From cache generated ".date('H:i', filemtime($cachefile))." -->\n";
   exit;
}
?>

<?php
   $cachefile = "cache/".$reqfilename.".html";
   $cachetime = 5 * 60; // 5 minutes
   // Serve from the cache if it is younger than $cachetime
   if (file_exists($cachefile) && (time() - $cachetime < filemtime($cachefile))) {
     include($cachefile);
     echo "<!-- Cached ".date('jS F Y H:i', filemtime($cachefile))." -->\n";
     exit;
   }
   ob_start(); // start the output buffer
?>

<?php
   $fp = fopen($cachefile, 'w'); // open the cache file for writing
   fwrite($fp, ob_get_contents()); // save the contents of output buffer to the file
   fclose($fp); // close the file
   ob_end_flush(); // Send the output to the browser
?>

<?php
  $cachefile = "cache/".$reqfilename.".html";
   // Serve from the cache if it is the same age or younger than the last
   // modification time of the included file (includes/$reqfilename)
   if (file_exists($cachefile) && (filemtime("includes/".$reqfilename)) < filemtime($cachefile))) {
     include($cachefile);
     echo "<!-- Cached ".date('H:i', filemtime($cachefile))." -->\n";
     exit;
   }
   ob_start(); // start the output buffer
?>

<?php
   $fp = fopen($cachefile, 'w'); // open the cache file for writing
   fwrite($fp, ob_get_contents()); // save the contents of output buffer to the file
   fclose($fp); // close the file
   ob_end_flush(); // Send the output to the browser
?>