RabbitMQ 消息优先级队列不工作

Question

我运行优先级队列 java program在我的 eclipse 中，我遇到了一个问题，我第一次得到正确答案。还有一次我在队列中添加了一条消息，但这次我得到了不同的结果。

public static void main(String[] argv) throws Exception {
     ConnectionFactory factory = new ConnectionFactory();
        Connection conn = factory.newConnection();
        Channel ch = conn.createChannel();
        Map<String, Object> args = new HashMap<String, Object>();
        args.put("x-max-priority", 10);
        ch.queueDeclare(QUEUE_UPDATE, true, false, false, args);

         publish(ch, 141);   
         publish(ch, 250);   

        final CountDownLatch latch = new CountDownLatch(2);
        ch.basicConsume(QUEUE_UPDATE, true, new DefaultConsumer(ch) {
            public void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties, byte[] body) throws IOException {
                System.out.println("Received " + new String(body));
                latch.countDown();
            }
        });

        latch.await();
        conn.close();           
        System.out.println("Finished");
}

private static void publish(Channel ch, int priority) throws Exception {
     BasicProperties props = MessageProperties.PERSISTENT_BASIC.builder().priority(priority).build();
     String body = QUEUE_UPDATE + " message with priority " + priority ;
     ch.basicPublish("", QUEUE_UPDATE, props, body.getBytes());         
}

正确的输出:

Received update-queue message with priority 250
Received update-queue message with priority 141
Finished

添加了一条队列消息

         publish(ch, 141);    
         publish(ch, 250);   
         publish(ch, 110); // newly added

预期输出

Received update-queue message with priority 250
Received update-queue message with priority 141
Received update-queue message with priority 110
Finished

实际输出

Received update-queue message with priority 141
Received update-queue message with priority 250
Received update-queue message with priority 110
Finished

怎么会变成这样？我做错了什么吗？

Answer 1

我遇到了同样的问题。对我有用的是定义由 consumer prefetch 定义的限制。 ，例如 channel.basicQos(1);。如果您不设置此限制，消息将在到达代理时传送给消费者，因此它们永远不会使用优先级进行排序。

当您设置下限时，代理不会一次发送超过此限制的消息，因此会在传递前对消息进行排序。