PHP Cache Dynamic Pages To Speed Up Load Times

pomosda Saran Chamling

If your website has hundreds of pages with many visitors everyday, you might want to implement some sort of caching mechanism for your website to speed up page loading time. Each client-server request consist of multiple database queries, server response and the processing time increasing overall page loading time. The most common solution is to make copies of dynamic pages called cache files and store them in a separate directory, which can later be served as static pages instead of re-generating dynamic pages again and again.

Understanding Dynamic pages & Cache Files

Cache files are static copies generated by dynamic pages, these files are generated one time and stored in separate folder until it expires, and when user requests the content, the same static file is served instead of dynamically generated pages, hence bypassing the need of regenerating HTML and requesting results from database over and over again using server-side codes. For example, running several database queries, calculating and processing PHP codes to the HTML output takes certain seconds, increasing overall page loading time with dynamic page, but a cached file consist of just plain HTML codes, you can open it in any text editor or browser, which means it doesn't require processing time at all.
Dynamic page : - The example in the picture below shows how a dynamic page is generated. As it's name say's, it's completely dynamic, it talks to database and generates the HTML output according to different variables user provides during the request. For example a user might want to list all the books by a particular author, it can do that by sending queries to database and generating fresh HTML content, but each request requires few seconds to process also the certain server memory is used, which is not a big deal if website receives very few visitors. However, consider hundreds of visitors requesting and generating dynamic pages from your website over and over again, it will considerably increase the pressure, resulting delayed output and HTTP errors on the client's browser.

Cached File :- Picture below illustrates how cached files are served instead of dynamic pages, as explained above the cached files are nothing but static web pages. They contain plain HTML code, the only way the content of the cached page will change is if the Web developer manually edits the file. As you can see cached files neither require database connectivity nor the processing time, it is an ideal solution to reduce server pressure and page loading time consistently.


PHP Caching

There are other ways to cache dynamic pages using PHP, but the most common method everyone's been using is PHP Output Buffer and Filesystem Functions, combining these two methods we can have magnificent caching system.
PHP Output buffer :- It interestingly improves performance and decreases the amount of time it takes to download, because the output is not being sent to browser in pieces but the whole HTML page as one variable. The method is insanely simple take a look at the code below :

ob_start(); // start the output buffer
/* the content */
ob_get_contents();  gets the contents of the output buffer 
ob_end_flush(); // Send the output and turn off output buffering

When you call ob_start() on the top of the code, it turns output buffering on, which means anything after this will be stored in the buffer, instead of outputting on the browser. The content in the buffer can be retrieved using ob_get_contents(). You should call ob_end_flush() at the end of the code to send the output to the browser and turn buffering off.

PHP Filesystem :- You may be familiar with PHP file system, it is a part of the PHP core, which allow us to read and write the file system. Have a look at the following code.

$fp = fopen('/path/to/file.txt', 'w');  //open file for writing
fwrite($fp, 'I want to write this');    //write 
fclose($fp);                            //Close file pointer

As you can see the first line of the code fopen() opens the file for writing, the mode 'w' places the file pointer at the beginning of the file and if file does not exist, it attempts to create one. Second line fwrite() writes the string to the opened file, and finally fclose() closes the successfully opened file at the beginning of the code.

Implementing PHP caching

Now you should be pretty clear about PHP output buffer and filesystem, we can use these both methods to create our PHP caching system. Please have a look at the picture below, the Flowchart gives us the basic idea about our cache system.

The cycle starts when a user request the content, we just check whether the cache copy exist for the currently requested page, if it doesn't exist we generate a new page, create cache copy and then output the result. If the cache already exist, we just have to fetch the file and send it to the user browser.
Take a look at the Full PHP cache code below, you can just copy and paste it in your PHP projects, it should work flawlessly as depicted in above Flowchart. You can play with the settings in the code, modify the cache expire time, cache file extension, ignored pages etc.

$cache_ext  = '.html'; //file extension
$cache_time = 3600;  //Cache file expires afere these seconds (1 hour = 3600 sec)
$cache_folder = 'cache/'; //folder to store Cache files
$ignore_pages = array('', ''); 

$dynamic_url = 'http://'.$_SERVER['HTTP_HOST'] 
                        // requested dynamic page (full url

$cache_file  = $cache_folder.md5($dynamic_url).$cache_ext; 
               // construct a cache file
$ignore = (in_array($dynamic_url,$ignore_pages))?true:false; 
          //check if url is in ignore list

if (!$ignore && file_exists($cache_file) 
    && time() - $cache_time < filemtime($cache_file)) 
      //check Cache exist and it's not expired.
      ob_start('ob_gzhandler');  //Turn on output buffering,
      //"ob_gzhandler" for the compressed page with gzip.
      //read Cache file
      echo '';
      ob_end_flush(); //Flush and turn off output buffering
      exit(); //no need to proceed further, exit the flow.
//Turn on output buffering with gzip compression.

######## Your Website Content Starts Below #########


######## Your Website Content Ends here ######### 

if (!is_dir($cache_folder)) { //create a new folder if we need to
    $fp = fopen($cache_file, 'w');  //open file for writing
    fwrite($fp, ob_get_contents()); //write contents of the output buffer in Cache file
    fclose($fp); //Close file pointer
ob_end_flush(); //Flush and turn off output buffering 

You must place your PHP content between the enclosed comment lines, In fact I'd suggest putting them in separate header and footer file, so that it can generate and serve cache files for all the different dynamic pages. If you read the comment lines in the code carefully, you should find it pretty much self explanatory.

1. Get the currently requested URL location.
2. Construct a location path for the cache file, convert URL to MD5 hash for the fixed cache file name.
3. Check whether URL is in ignore list.
4. Check for existing unexpired cache file, if exist, just open and output the content with gzip compression.
5. Or else, we create a new cache file and output the HTML result with gzipcompression.

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  • 15 Sep 2014
  • By Saran Chamling
  • PHP-5
  • 1809 Read