Zend Framework

class KeyEnabled_Memcached extends Zend_Cache_Backend_Memcached
{

	private function getTagListId()
	{
		return "MyTagArrayCacheKey";
	}
	
	private function getTags()
	{
		if(!$tags = $this->_memcache->get($this->getTagListId()))
		{
			$tags = array();
		}
		return $tags;
	}
	
	private function saveTags($id, $tags)
	{
		// First get the tags
		$siteTags = $this->getTags();
		
		foreach($tags as $tag)
		{
			$siteTags[$tag][] = $id;
		}
		$this->_memcache->set($this->getTagListId(), $siteTags);		
	}
	
	private function getItemsByTag($tag)
	{
		$siteTags = $this->_memcache->get($this->getTagListId());
		return isset($siteTags[$tag]) ? $siteTags[$tag] : false;
	}

    /**
     * Save some string datas into a cache record
     *
     * Note : $data is always "string" (serialization is done by the
     * core not by the backend)
     *
     * @param  string $data             Datas to cache
     * @param  string $id               Cache id
     * @param  array  $tags             Array of strings, the cache record will be tagged by each string entry
     * @param  int    $specificLifetime If != false, set a specific lifetime for this cache record (null => infinite lifetime)
     * @return boolean True if no problem
     */
    public function save($data, $id, $tags = array(), $specificLifetime = false)
    {
        $lifetime = $this->getLifetime($specificLifetime);
        if ($this->_options['compression']) {
            $flag = MEMCACHE_COMPRESSED;
        } else {
            $flag = 0;
        }
        $result = $this->_memcache->set($id, array($data, time()), $flag, $lifetime);
        if (count($tags) > 0) {
        	$this->saveTags($id, $tags);
        }
        return $result;
    }

    /**
     * Clean some cache records
     *
     * Available modes are :
     * 'all' (default)  => remove all cache entries ($tags is not used)
     * 'old'            => remove too old cache entries ($tags is not used)
     * 'matchingTag'    => remove cache entries matching all given tags
     *                     ($tags can be an array of strings or a single string)
     * 'notMatchingTag' => remove cache entries not matching one of the given tags
     *                     ($tags can be an array of strings or a single string)
     *
     * @param  string $mode Clean mode
     * @param  array  $tags Array of tags
     * @return boolean True if no problem
     */
    public function clean($mode = Zend_Cache::CLEANING_MODE_ALL, $tags = array())
    {
        if ($mode==Zend_Cache::CLEANING_MODE_ALL) {
            return $this->_memcache->flush();
        }
        if ($mode==Zend_Cache::CLEANING_MODE_OLD) {
            $this->_log("Zend_Cache_Backend_Memcached::clean() : CLEANING_MODE_OLD is unsupported by the Memcached backend");
        }
        if ($mode==Zend_Cache::CLEANING_MODE_MATCHING_TAG) {
        	$siteTags = $newTags = $this->getTags();
        	if(count($siteTags))
        	{
	        	foreach($tags as $tag)
	        	{
	        		if(isset($siteTags[$tag]))
	        		{
	        			foreach($siteTags[$tag] as $item)
	        			{
	        				// We call delete directly here because the ID in the cache is already specific for this site
	        				$this->_memcache->delete($item);
	        			}
	        			unset($newTags[$tag]);
	        		}
	        	}
	        	$this->_memcache->set($this->getTagListId(),$newTags);
        	}
        }
        if ($mode==Zend_Cache::CLEANING_MODE_NOT_MATCHING_TAG) {
        	$siteTags = $newTags = $this->getTags();
        	if(count($siteTags))
        	{
        		foreach($siteTags as $siteTag => $items)
        		{
        			if(array_search($siteTag,$tags) === false)
        			{
        				foreach($items as $item)
        				{
        					$this->_memcache->delete($item);
        				}
        				unset($newTags[$siteTag]);
        			}
        		}
        		$this->_memcache->set($this->getTagListId(),$newTags);
        	}
        }
    }
}