private static function _getMemcachePrefix()
 {
     if (!isset(self::$_cacheNamespace)) {
         $mc = self::getMemcache();
         //namespace is incremented in Kwf_Util_ClearCache
         //use memcache directly as Zend would not save the integer directly and we can't increment it then
         $v = $mc->get(self::getUniquePrefix() . 'cache_namespace');
         if (!$v) {
             $v = time();
             $mc->set(self::getUniquePrefix() . 'cache_namespace', $v);
         }
         self::$_cacheNamespace = self::getUniquePrefix() . '-' . $v;
     }
     return self::$_cacheNamespace;
 }