Codeigniter page caching with query string

Fig: Basic Page Cache Flow

CodeIgniter lets you cache your pages in order to achieve maximum performance. When a page is loaded for the first time, the cache file will be written to your application/cache folder.
To enable caching, put the following tag in any of your controller functions:

$this->output->cache(n);

Where n is the number of minutes you wish the page to remain cached between refreshes.

Warning: Because of the way CodeIgniter stores content for output, caching will only work if you are generating display for your controller with a view.

Problem:

It work only with segment based url. 

What I'm seeing in my use cases and in the Output class code is that the caching is solely segment based. As such, http://www.example.com/segment/?q=foo andhttp://www.example.com/segment/?q=bar are treated as identical requests.

If you want your caching to  work for query string as well,
You can just copy that code below and put it in application/core/MY_Output.php .

<?php



/**

 * @author vee

 * @copyright http://www.okvee.net

 */



class MY_Output extends CI_Output {

     

     

    function __construct() {

        parent::__construct();

    }// __construct

     

     

    /**

     * Update/serve a cached file

     *

     * @access    public

     * @return    void

     */

    function _display_cache(&$CFG, &$URI)

    {

        $cache_path = ($CFG->item('cache_path') == '') ? APPPATH.'cache/' : $CFG->item('cache_path');



        // Build the file path.  The file name is an MD5 hash of the full URI

        $uri =    $CFG->item('base_url').

                $CFG->item('index_page').

                $URI->uri_string;

        // buld query strings

        $querystrings = $_SERVER['QUERY_STRING'];

        if ( $querystrings != null ) {$querystrings = "?".$querystrings;}

        $uri = $uri.$querystrings;



        $filepath = $cache_path.md5($uri);



        if ( ! @file_exists($filepath))

        {

            return FALSE;

        }



        if ( ! $fp = @fopen($filepath, FOPEN_READ))

        {

            return FALSE;

        }



        flock($fp, LOCK_SH);



        $cache = '';

        if (filesize($filepath) > 0)

        {

            $cache = fread($fp, filesize($filepath));

        }



        flock($fp, LOCK_UN);

        fclose($fp);



        // Strip out the embedded timestamp

        if ( ! preg_match("/(\d+TS--->)/", $cache, $match))

        {

            return FALSE;

        }



        // Has the file expired? If so we'll delete it.

        if (time() >= trim(str_replace('TS--->', '', $match['1'])))

        {

            if (is_really_writable($cache_path))

            {

                @unlink($filepath);

                log_message('debug', "Cache file has expired. File deleted");

                return FALSE;

            }

        }



        // Display the cache

        $this->_display(str_replace($match['0'], '', $cache));

        log_message('debug', "Cache file is current. Sending it to browser.");

        return TRUE;

    }// _display_cache

     

     

    /**

     * Write a Cache File

     *

     * @access    public

     * @return    void

     */

    function _write_cache($output)

    {

        $CI =& get_instance();

        $path = $CI->config->item('cache_path');



        $cache_path = ($path == '') ? APPPATH.'cache/' : $path;



        if ( ! is_dir($cache_path) OR ! is_really_writable($cache_path))

        {

            log_message('error', "Unable to write cache file: ".$cache_path);

            return;

        }



        $uri =    $CI->config->item('base_url').

                $CI->config->item('index_page').

                $CI->uri->uri_string();

        // buld query strings

        $querystrings = $_SERVER['QUERY_STRING'];

        if ( $querystrings != null ) {$querystrings = "?".$querystrings;}

        $uri = $uri.$querystrings;



        $cache_path .= md5($uri);



        if ( ! $fp = @fopen($cache_path, FOPEN_WRITE_CREATE_DESTRUCTIVE))

        {

            log_message('error', "Unable to write cache file: ".$cache_path);

            return;

        }



        $expire = time() + ($this->cache_expiration * 60);



        if (flock($fp, LOCK_EX))

        {

            fwrite($fp, $expire.'TS--->'.$output);

            flock($fp, LOCK_UN);

        }

        else

        {

            log_message('error', "Unable to secure a file lock for file at: ".$cache_path);

            return;

        }

        fclose($fp);

        @chmod($cache_path, FILE_WRITE_MODE);



        log_message('debug', "Cache file written: ".$cache_path);

    }// _write_cache

     

     

}
 

Ref: codeigniter cache with querystring, Web Page Caching