Cache PHP output for high traffic websites. PEAR: Cache_Lite

Intro…

Now days the WebPages are outcome of heavy script processing in order to provide more dynamicity to page visitors. The utility of server side scripting is to adopt more engineering on web. When the page gets more visitors or becomes more popular, you have to ensure that, that traffic doesn’t stack or queued in front of your freaky web server. All you have to do is to serve them with your page and ofcourse serve it faster. Again server side scripting requires processing and compiling.

In order to serve pages faster, to make light use of server side processing and compiling and to survive within heavy traffic, caching dynamic script output is needed.

The Need For Speed…

Every time a request hits your web server, PHP has to do a lot of processing, all of your codes have to be compiled and executed for a single traffic hit every time. Interesting thing will be if the outcomes of all these processing is identical for each visitors. Say, processing happens every time for visitor 24500 and 24501 while the outputs are so same. Argh!!

What would be if we save the flat HTML generated for visitor 24500 and serve that to 24501 as well??? That will be awesome 😀 coz this leads to less processing and faster page handover. This da mechanism we are talking about, yeah! Cache PHP output 😀

Well we can write such optimization system but there is a smart package in PEAR called Cache_Lite that can do this job for us. Let’s check out why Cache_Lite:

  • It saves time of writing new caching codes 😀
  • It’s optimized for high traffic websites
  • Robust, easy to implement
  • Have time to time documentation
  • Bunch of cool features. 🙂

Installation…

The Cache_Lite class comes courtesy of PEAR, the “PHP Extension and Application Repository” (http://pear.php.net). In case you didn’t know, PEAR is an online repository of free PHP software, including classes and modules for everything from data archiving to XML parsing. When you install PHP, a whole bunch of PEAR modules get installed as well; the Cache_Lite class is one of them.

In case not installed then…

It is just like coding hello world!! 😀

On ubuntu:

sudo aptitude -y update
sudo aptitude install php-pear

Now that we have PEAR, i would use it to install the Cache_Lite extension

sudo pear install Cache_Lite

Perfect! 😀

Checking whether installed/ checking PEAR verson:

Both pear and pecl tools should be available everywhere on command line. For that to work, pear’s binary (bin) directory should be in your PATH variable.

To verify it works, simply type pear. A list of commands should be shown:

$ pear
Commands:
build                  Build an Extension From C Source
bundle                 Unpacks a Pecl Package
channel-add            Add a Channel
...

You should further test that PEAR is up to date:

$ pear version
PEAR Version: 1.7.2
PHP Version: 5.2.6RC4-pl0-gentoo
Zend Engine Version: 2.2.0
Running on: Linux ...

More installation queries here: http://pear.php.net/manual/en/installation.checking.php

Implementation…

<?php

// Include the package
require_once('Cache/Lite.php'); // make sure cache_lite script path

// Set a id for this cache
$id = '123';

// Set a few options
$options = array(
    'cacheDir' => '/tmp/',
    'lifeTime' => 3600
);

// Create a Cache_Lite object
$Cache_Lite = new Cache_Lite($options);

// Test if thereis a valide cache for this id
if ($data = $Cache_Lite->get($id)) {

    // Cache hit !
    // Content is in $data
    // (...)

} else { // No valid cache found (you have to make the page)

    // Cache miss !
    // Put in $data datas to put in cache
    // (...)
    $Cache_Lite->save($data);

}

?>

 

More clearly…


<?php
require_once "Cache/Lite.php";

$options = array(
    'cacheDir' => '/tmp/',
    'lifeTime' => 7200,
    'pearErrorMode' => CACHE_LITE_ERROR_DIE
);
$cache = new Cache_Lite($options);

if ($data = $cache->get('id_of_the_page')) {

    // Cache hit !
    // Content is in $data
    echo $data;

} else {

    // No valid cache found (you have to make and save the page)
    $data = '<html><head><title>test</title></head><body><p>this is a test</p></body></html>';
    echo $data;
    $cache->save($data);

}

?>

If you wish use a cache per block and not a global cache, take as example the following script:

<?php
require_once('Cache/Lite.php');

$options = array(
    'cacheDir' => '/tmp/',
    'lifeTime' => 3600
);

// Create a Cache_Lite object
$Cache_Lite = new Cache_Lite($options);

if ($data = $Cache_Lite->get('block1')) {
    echo($data);
} else {
    $data = 'Data of the block 1';
    $Cache_Lite->save($data);
}

echo('<br><br>Non cached line !<br><br>');

if ($data = $Cache_Lite->get('block2')) {
    echo($data);
} else {
    $data = 'Data of the block 2';
    $Cache_Lite->save($data);
}

?>

Little bit implementation:

The key point is Cache_Lite maintains a unique identifier for every page. Cache_Lite will check for that identifier used before. If so, it will retrieve the stored HTML from disk (can use RAM as turbo charged storage i.e. mount tmpfs in RAM memory) and echo it right away. If not, we:

  • turn on output buffereing so we can catch all following content
  • we include the original PHP code
  • catch the output buffer, and let Cache_Lite store it on disk for the next time.
  • and then echo it

Example:

<?php

/* Include the class */
require_once 'Cache/Lite.php';

/* Set a key for this cache item */
$id = 'newsitem1';

/* Set a few options */
$options = array(
    'cacheDir' => '/var/www/www.mywebsite.com/cache/',
    'lifeTime' => 3600
);

/* Create a Cache_Lite object */
$Cache_Lite = new Cache_Lite($options);

/* Test if there is a valid cache-entry for this key */
if ($data = $Cache_Lite->get($id)) {
    /* Cache hit! We've got the cached content stored in $data! */
} else {
    /* Cache miss! Use ob_start to catch all the output that comes next*/
    ob_start();

    /* The original content, which is now saved in the output buffer */
    include "requiredPhpFile.php";

    /* We've got fresh content stored in $data! */
    $data = ob_get_contents();

    /* Let's store our fresh content, so next
     * time we won't have to generate it! */
    $Cache_Lite->save($data, $id);
    ob_get_clean();
}
echo $data;

?>

A Special case…

Say a case, is to automatically purge an article’s cache when a comment has been placed. You could for example place this before Cache_Lite checks if it’s got a cache page for a specific $id:


<?php
if(isset($_POST["add_comment"]) && $_POST["add_comment"]){
    $Cache_Lite->remove($id);
}

?>

Docs for Cahe_Lite here:

http://pear.php.net/manual/en/package.caching.cache-lite.php

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