rabbitmq+pika 中，每个消费者获取消息数量的问题。

环境 pika 0.10 RabbitMQ 3.5.4, Erlang 18.0

生产者

connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
channel = connection.channel()

queue_name="route_test"

channel.exchange_declare(exchange='logs')
channel.basic_qos(prefetch_count=1)

message = ' '.join(sys.argv[1:]) or "info: Hello World!"
i = 0
while i < 10:
    channel.basic_publish(exchange='logs',
                          routing_key=queue_name,
                          body=message,
                          properties=pika.BasicProperties(
                              delivery_mode=2
                          ))
    i += 1

print(" [x] Sent %r" % message)
connection.close()

消费者

def on_start():
    connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
    channel = connection.channel()

    queue_name="route_test"
    channel.exchange_declare(exchange='logs')

    channel.queue_declare(queue=queue_name)
    channel.queue_bind(exchange='logs',
                   queue=queue_name)

    channel.basic_qos(prefetch_count=1)
    channel.basic_consume(callback,
                      queue=queue_name,
                      no_ack=True)
    return channel


def callback(ch, method, properties, body):
    print(" [x] %r" % body)
    time.sleep(3)

while True:
    try:
        channel = on_start()
        print(' [*] Waiting for logs. To exit press CTRL+C')
        channel.start_consuming()
    except:
        print "connect error"

我已经在 channel 中设置了channel.basic_qos(prefetch_count=1)，但是我如果先执行消费者，然后再执行生产者，就会一次性的把所有的消息都扔给消费者，这样，我如果手动再启动一个消费者，就无法获得还没有被执行的消息了。

请问，这是为什么，或者怎么样能够达到我想要的效果，即每次消费者都只获得一个消息，剩下的都保存在消息队列里面。