can't get the value of cache

i want to use memcache of yii.

now,in main.php,i had configure the code like this,

    'cache'=>array(


        'class'=>'CMemCache',


        'servers'=>array(


            array(


                'host'=>'127.0.0.1',


                'port'=>11211,


            ),


        ),


		'keyPrefix' => '',     


	    'hashKey' => false,     


 	    'serializer' => false

and in controller,

	$key = 'people'; 


$value = json_encode(array('name'=>'ball', 'age'=>'male')); 


$expire = 60; 


if(Yii::app()->cache->set($key, $value, $expire))


	echo "insert success";


else


	echo "insert failed";


$gg = Yii::app()->cache->get($key); 


print_r($gg);


exit();

now ,insert success had showed,but i can’t get $gg’value,

what’s the matter.