Speed up your apps and have a convenient application-level scope with AppCache by Chris Dary, the seventh tool from the arc90 lab.
- What is this?
- How do I use it?
- Why is this better than using Memcache directly?
- Examples
- Download the Code
- Prerequisites
- Licensing
- Discuss AppCache
What is this?
AppCache is an implementation of an Application scope in PHP. If you’ve ever worked with Coldfusion (or ASP), you’ll know that Application-level variables are visible to an entire group of files. They’re one level above a session scope, and one level below server level variables.
As you can probably guess, this is hugely useful for all sorts of things – things like caching data, common variables, etc.
To do this, AppCache expands upon a fantastic caching system called memcached. Memcached’s intent is to speed up web applications by alleviating database load – it was originally created to enhance the speed of LiveJournal.com.
As a caveat, if you have not used an Application scope or a caching mechanism before: This data is not persistent – it’s stored in RAM, not on disk, and will be lost if the daemon is restarted or the cache expires, and therefore you should only use it for run-time stuff, which can be recreated or retrieved every time the app starts.
Why is this better than using Memcache directly?
- In your code, usage is very clean – as simple as
$app->var; - Unlike Memcache itself, you have access to the list of variables defined within your app –
$app->getKeys();returns an array of all the currently defined variables. Useisset($app->var)to determine if a variable is set. - No namespace worries. A key prefix is created from whatever you name the app – so you don’t have to worry about collisions with other memcache keys.
- The Memcache backend is abstracted – so if you end up implementing a different backend (database, shared memory, etc), this should be very simple.
Examples
Here are a few examples of what AppCache looks like in action:
A Simple Example
<?php
require 'Application.php';
// Initialize our application
$app = new Application('Sample Application Name');
// Check if our sample value is set
if( !isset( $app->sampleValue ) )
{
// If it is not set, initialize it, with the date, so that we can
// see that it is persistent amongst requests.
$app->sampleValue = "This sample value was set on " . date('r');
}
// Print our sample value
print_r($app->sampleValue);
// To remove sampleValue from our app, we would use:
// unset($app->sampleValue);
// To flush all values from the app, we would use:
// $app->clear();
// To access $app within functions and other classes, use either
// $GLOBALS['app'] or global $app;, then $app.
?>
A More Complex Example
<?php
require 'Application.php';
// Here, we pass our Application constructor an array of values for configuration.
$app = new Application(
array(
'key' => 'A complex Application example',
'memcached_servers' => array('127.0.0.1:11211','anotherHost.com:22122'),
'memcached_prefix' => 'appvar_'
)
);
// Set up a cached_page variable that will expire.
if( !isset( $app->cached_page ) )
{
$page_content = array();
$page_content['header'] = '<html><head>' .
'<title>Page cached on ' . date('r') . '</title>' .
'</head><body>' .
'<h1>This is a cached header</h1>';
$page_content['body'] = '<p>This is some cached body content ' .
'with a random number: ' . rand() . '</p>';
$page_content['footer'] = '<h5>This is a cached footer</h5>' .
'</body></html>';
// This content will expire and be regenerated every 15 seconds
$app->setWithExpire('cached_page', $page_content, 15);
}
echo $app->cached_page['header'];
echo '<h4>The date is ' . date('r') . '. This is not cached.</h4>';
echo $app->cached_page['body'];
echo $app->cached_page['footer'];
// To see a list of all keys in our app,
// and their expiration dates (if they have one), use:
// print_r($app->getKeys());
// To remove cached_page from our app, we would use:
// unset($app->cached_page);
// To flush all values from the app, we would use:
// $app->clear();
?>
Download The Code
To use AppCache on your site, download it from one of the following sources:
Source File with Examples
This is a zip file with Application.php as well as the two examples above.
Raw Source File
This is just Application.php as a PHP source file.
Prerequisites
To run AppCache, you need the following:
- PHP 5. AppCache has been tested with PHP 5.2.0, but it will likely work with other versions of PHP 5 as well.
- An instance of memcached running somewhere. You can download it at http://www.danga.com/memcached.
- The PHP library for memcache – installed easily with PECL. In many cases it’s as simple as running
pecl install memcache. More information is available at http://us2.php.net/memcache.
Licensing
This arc90 tool is licensed under the Creative Commons Attribution 3.0 license.
Discuss AppCache
You can send feedback on AppCache at the arc90 blog.