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Function Reference/WP Cache

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Role of WP_Cache

WP_Object_Cache is WordPress' class for caching data which may be computationally intensive to regenerate dynamically on every page load. It's defined in wp-includes/cache.php.

Do not use the class directly in your code when writing plugins, but use the wp_cache functions listed here.

Caching to file to store the information across page loads is not enabled by default - this can be enabled by adding define('WP_CACHE', true); to your wp-config.php file.

Tip: Make sure define('WP_CACHE', true); is above this block: 

 /* That's all, stop editing! Happy blogging. */
 if ( !defined('ABSPATH') )
       define('ABSPATH', dirname(__FILE__) . '/');
    require_once(ABSPATH . 'wp-settings.php');

Within a single page loading caching does still occur so as to reduce the number of database queries as much as possible

wp_cache functions

Almost all of these functions take a:

  • key: the key to indicate the value
  • $data: the value you want to store
  • flag: optional: this is a way of grouping your cache data. If you use a flag, your data will be stored in a subdirectory of your cache directory
  • expire: number of seconds (by default 900) 
wp_cache_add($key, $data, $flag = '', $expire = 0)

This function first checks if there is a cached object on the given $key. If not, then it is saved, otherwise returns false. 

wp_cache_delete($id, $flag = '')

Clears a given file. 

wp_cache_get($id, $flag = '')

Gives back the value of the cached object if it did not expired. Otherwise gives back false. 

wp_cache_replace($key, $data, $flag = '', $expire = 0)

Replaces the given cache if it exists, returns false otherwise. 

wp_cache_set($key, $data, $flag = '', $expire = 0)

Sets the value of the cache object. If the object already exists, then it will be overwritten, if the object does not exists it will be created. 

wp_cache_init()

Initializes a new cache object. This function is called by Wordpress at initialization if cacheing is enabled. 

wp_cache_flush()

Clears all the cache files. 

wp_cache_close()

Saves the cached object. This function is called by Wordpress at the shutdown action hook.

Examples

You can use WP_Object_Cache and Snoopy to cache offsite includes: 

$news = wp_cache_get('news');
if($news == false) {
	$snoopy = new Snoopy;
	$snoopy->fetch('http://example.com/news/'); 
	$news = $snoopy->results;
	wp_cache_set('news', $news);
} 
echo $news;


Additional Resources

  • Dougal Campbell wrote a short guide on how to use the WordPress Cache object from within your own plugins : Using the WordPress Object Cache
  • Jeff Starr discusses different caching options and explains how to enable the default WordPress Object Cache : How to Enable the Default WordPress Object Cache
  • Peter Westwood has a plugin to help people analyze the behavior of the cache, provides the administrator with a quick overview of how the cache is performing and what queries are cached : WP Cache Inspect
  • Frank Bültge has written a new version of the plugin WP Cache Inspect by Peter Westwood for WordPress 2.7. The plugin helps to analyze the cache and optimize the cache on process in the backend of WordPress.  : WP Cache Inspect
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