RabbitMQ 消息丢失问题

一、Bug 场景

在一个电商系统中，使用 RabbitMQ 来处理订单相关的异步消息。例如，当用户下单后，系统会发送一条订单创建的消息到 RabbitMQ，由专门的消费者服务来处理订单后续的操作，如库存扣减、订单状态更新等。

二、代码示例

生产者代码（简化的 Java 示例）

import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.Channel;

public class OrderProducer {
    private static final String QUEUE_NAME = "order_queue";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {
            channel.queueDeclare(QUEUE_NAME, false, false, false, null);
            String message = "新订单创建";
            channel.basicPublish("", QUEUE_NAME, null, message.getBytes("UTF-8"));
            System.out.println(" [x] Sent '" + message + "'");
        }
    }
}

消费者代码（简化的 Java 示例）

import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import com.rabbitmq.client.AMQP;

public class OrderConsumer {
    private static final String QUEUE_NAME = "order_queue";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        channel.queueDeclare(QUEUE_NAME, false, false, false, null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        channel.basicConsume(QUEUE_NAME, true,
                "orderConsumerTag",
                (consumerTag, delivery) -> {
                    String message = new String(delivery.getBody(), "UTF-8");
                    System.out.println(" [x] Received '" + message + "'");
                    // 模拟订单处理业务逻辑
                    processOrder(message);
                },
                consumerTag -> {
                    System.out.println("Consumer cancelled: " + consumerTag);
                });
    }

    private static void processOrder(String message) {
        // 模拟订单处理
        System.out.println("订单处理中: " + message);
    }
}

三、问题描述

1. 预期行为：生产者发送的订单消息能可靠地被消费者接收并处理，不会出现消息丢失的情况。

2. 实际行为：在某些情况下，如生产者发送消息后 RabbitMQ 服务器重启，或者消费者处理消息过程中突然崩溃，消息可能会丢失。

   • 生产者端：在上述生产者代码中，basicPublish 方法调用后并没有确认机制来确保消息已被 RabbitMQ 服务器正确接收。如果在消息发送到服务器但还未被持久化时服务器重启，消息就会丢失。
   • 消费者端：在消费者代码中，basicConsume 方法的第二个参数 autoAck 设置为 true，这意味着消费者一旦接收到消息，RabbitMQ 就会自动将其从队列中删除。如果消费者在处理消息过程中崩溃，还未处理完的消息就会丢失。

四、解决方案

生产者端

1. 开启发布确认机制：

   import com.rabbitmq.client.ConnectionFactory;
   import com.rabbitmq.client.Connection;
   import com.rabbitmq.client.Channel;
   import com.rabbitmq.client.ConfirmCallback;
   
   public class OrderProducer {
       private static final String QUEUE_NAME = "order_queue";
   
       public static void main(String[] argv) throws Exception {
           ConnectionFactory factory = new ConnectionFactory();
           factory.setHost("localhost");
           try (Connection connection = factory.newConnection();
                Channel channel = connection.createChannel()) {
               channel.queueDeclare(QUEUE_NAME, true, false, false, null);
               channel.confirmSelect();
               channel.addConfirmListener((sequenceNumber, multiple) -> {
                   if (multiple) {
                       System.out.println("Multiple messages confirmed up to sequence number: " + sequenceNumber);
                   } else {
                       System.out.println("Message with sequence number: " + sequenceNumber + " confirmed");
                   }
               }, (sequenceNumber, multiple) -> {
                   System.out.println("Message(s) with sequence number(s) up to: " + sequenceNumber + " were not confirmed");
               });
   
               String message = "新订单创建";
               channel.basicPublish("", QUEUE_NAME, null, message.getBytes("UTF-8"));
               System.out.println(" [x] Sent '" + message + "'");
           }
       }
   }
   

   上述代码中，通过 channel.confirmSelect() 开启发布确认机制，并添加确认监听器，确保消息成功发送到 RabbitMQ 服务器。

消费者端

1. 关闭自动确认，手动确认消息：

   import com.rabbitmq.client.ConnectionFactory;
   import com.rabbitmq.client.Connection;
   import com.rabbitmq.client.Channel;
   import com.rabbitmq.client.DefaultConsumer;
   import com.rabbitmq.client.Envelope;
   import com.rabbitmq.client.AMQP;
   
   public class OrderConsumer {
       private static final String QUEUE_NAME = "order_queue";
   
       public static void main(String[] argv) throws Exception {
           ConnectionFactory factory = new ConnectionFactory();
           factory.setHost("localhost");
           Connection connection = factory.newConnection();
           Channel channel = connection.createChannel();
   
           channel.queueDeclare(QUEUE_NAME, true, false, false, null);
           System.out.println(" [*] Waiting for messages. To exit press CTRL+C");
   
           channel.basicConsume(QUEUE_NAME, false,
                   "orderConsumerTag",
                   (consumerTag, delivery) -> {
                       String message = new String(delivery.getBody(), "UTF-8");
                       System.out.println(" [x] Received '" + message + "'");
                       try {
                           // 模拟订单处理业务逻辑
                           processOrder(message);
                           channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
                       } catch (Exception e) {
                           channel.basicNack(delivery.getEnvelope().getDeliveryTag(), false, true);
                       }
                   },
                   consumerTag -> {
                       System.out.println("Consumer cancelled: " + consumerTag);
                   });
       }
   
       private static void processOrder(String message) {
           // 模拟订单处理
           System.out.println("订单处理中: " + message);
       }
   }
   

   在上述代码中，将 basicConsume 的 autoAck 设置为 false，消费者处理完消息后手动调用 basicAck 确认消息，若处理失败则调用 basicNack 并根据情况决定是否重新入队，从而避免消息丢失。同时，将队列声明为持久化（queueDeclare 的第一个参数设为 true），保证 RabbitMQ 服务器重启后队列和消息依然存在。