How can we exactly do caching in php [closed]

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I am a fresher to web development.

In开发者_StackOverflow my application I need to have caching so any one can explain me how to do caching of PHP pages in detail?

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First make a folder called cache at the root of your site and make it writeable.

I have a file called caching_functions.php that looks like this:

<?
$test_server = $_SERVER['SERVER_NAME'] == "127.0.0.1" || $_SERVER['SERVER_NAME'] == "localhost" || substr($_SERVER['SERVER_NAME'],0,3) == "192";

$caching = !$test_server;

function start_caching($page) {

    global $caching;

    $hash = md5($page);

    if ($caching) {
        $cachefile = "cache/".$hash.".html";

        if (file_exists($cachefile)) {
            include($cachefile);
            echo "<!-- Cached on ".gmdate('r', filemtime($cachefile))." to ".$hash." -->";      
            exit;
        } else {
            ob_start();
            return $cachefile;  
        }       
    }
}

function end_caching($cachefile) {
    global $caching;    
    if ($caching) {     
        $fp = fopen($cachefile, 'w'); 
//      fwrite($fp, ob_get_contents());
        fwrite($fp, preg_replace('!\s+!', ' ', str_replace(array("\n", "\t"),"",ob_get_contents())));
        fclose($fp); 

        ob_end_flush();     
    }
}

function remove_cache() {

    foreach (glob($_SERVER['DOCUMENT_ROOT']."/cache/*.*") as $filename) {
        unlink($filename);
    }
}


?>

I then put at the top of each page:

and at the bottom:

<? end_caching($cachefile); ?>

This makes the first request for a page get dumped to the cache folder. Subsequent visits use the cached version, and don't hit the database or do anything complex.

I'd make a page called clearcache.php and include the caching_functions and get it just to run remove_cache(). That will let you easily remove the cached files when needed.

This also only runs when not local, so make sure that you either change $caching to 1 if you want to test locally, or only test on a real server.

---

Caching in PHP can be mean storing the results of a particular function last time it was called in case that function is called multiples times in the same script (with the same parameters).

However I think the main and more powerful meaning is storing the complete output of a dynamically generated page, and serving this up when the page is requested again instead of actually running the full PHP script to regenerate that content.

For pages I want to cache, I have an AJAX command that writes the content into a database after the page is generated. It also adds an expiry time - say time() + 20 (expire in 20 seconds).

Then I add a condition at the top of the page to check for an unexpired cache for the page in the database. If found it returns that, otherwise it continues to re-generate the full page.

This article helped me get started:

http://simas.posterous.com/php-data-caching-techniques