死信队列简介
RabbitMQ 的死信队列（Dead Letter Queue）是一种特殊的队列，用于存储那些被标记为“死信”的消息。所谓死信即无法被正常消费和处理的消息，通常是由于一些特定的情况或条件导致的，比如过期、重试次数超过限制等。
普通消息成为死信的常见原因有
- 消息被拒(basic.reject or basic.nack)丢弃消息(requeue=false)；
- 消息过期：当消息的生存周期超过了设置的过期时间，即消息在队列中等待被消费的时间超过了预定的时间。（可以通过设置 x-message-ttl 参数来指定消息的过期时间 或者 可以为每条消息单独设置过期时间。通过在消息的属性中设置 expiration 字段，以毫秒为单位指定消息的过期时间）
- 队列达到最大长度：当队列中的消息数量超过了设置的最大长度时，新到达的消息无法进入队列，而被视为死信。(创建队列时指定" x-max-length参数设置队列最大消息数量)
死信处理过程
消息被拒
class Program
{
static IConnectionFactory factory = new ConnectionFactory()
{
HostName = "192.168.100.2",
UserName = "uat",
Password = "137955aaA",
VirtualHost = "uat_vhost"
};
/// <summary>
/// 生产者
/// </summary>
public static void SendMessage()
{
//死信交换机
string dlxexChange = "dlx.exchange";
//死信队列
string dlxQueueName = "dlx.queue";
//消息交换机
string exchange = "direct.exchange";
//消息队列
string queueName = "direct.queue";
using (var connection = factory.CreateConnection())
{
using (var channel = connection.CreateModel())
{
//创建死信交换机
channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建死信队列
channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false);
//死信队列绑定死信交换机
channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName);
// 创建消息交换机
channel.ExchangeDeclare(exchange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建消息队列,并指定死信队列
channel.QueueDeclare(queueName, durable: true, exclusive: false, autoDelete: false, arguments:
new Dictionary<string, object> {
{ "x-dead-letter-exchange",dlxexChange}, //设置当前队列的DLX(死信交换机)
{ "x-dead-letter-routing-key",dlxQueueName}, //设置DLX的路由key，DLX会根据该值去找到死信消息存放的队列
});
//消息队列绑定消息交换机
channel.QueueBind(queueName, exchange, routingKey: queueName);
string message = "hello rabbitmq message";
var properties = channel.CreateBasicProperties();
properties.Persistent = true;
//发布消息
channel.BasicPublish(exchange: exchange,
routingKey: queueName,
basicProperties: properties,
body: Encoding.UTF8.GetBytes(message));
Console.WriteLine($"向队列:{queueName}发送消息:{message}");
}
}
}
/// <summary>
/// 消费者
/// </summary>
public static void Consumer()
{
//死信交换机
string dlxexChange = "dlx.exchange";
//死信队列
string dlxQueueName = "dlx.queue";
//消息交换机
string exchange = "direct.exchange";
//消息队列
string queueName = "direct.queue";
var connection = factory.CreateConnection();
{
//创建信道
var channel = connection.CreateModel();
{
//创建死信交换机
channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建死信队列
channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false);
//死信队列绑定死信交换机
channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName);
// 创建消息交换机
channel.ExchangeDeclare(exchange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建消息队列,并指定死信队列
channel.QueueDeclare(queueName, durable: true, exclusive: false, autoDelete: false, arguments:
new Dictionary<string, object> {
{ "x-dead-letter-exchange",dlxexChange}, //设置当前队列的DLX
{ "x-dead-letter-routing-key",dlxQueueName}, //设置DLX的路由key，DLX会根据该值去找到死信消息存放的队列
});
//消息队列绑定消息交换机
channel.QueueBind(queueName, exchange, routingKey: queueName);
var consumer = new EventingBasicConsumer(channel);
channel.BasicQos(prefetchSize: 0, prefetchCount: 1, global: true);
consumer.Received += (model, ea) =>
{
//处理业务
var message = Encoding.UTF8.GetString(ea.Body.ToArray());
Console.WriteLine($"队列{queueName}消费消息:{message},不做ack确认");
//不ack(BasicNack),且不把消息放回队列(requeue:false)
channel.BasicNack(ea.DeliveryTag, false, requeue: false);
};
channel.BasicConsume(queueName, autoAck: false, consumer);
}
}
}
static void Main(string[] args)
{
SendMessage();
Consumer();
Console.ReadLine();
}
}
不ack(BasicNack),且不把消息放回队列(requeue:false)，产生死信队列
延时队列（相同的过期时间）
延时队列通常与死信队列结合使用，以实现消息的延迟投递和处理。它的基本思想是给消息队列设置消息的过期时间（TTL），当消息在一定时间内未被消费者处理时，将其标记为过期并发送到死信队列。
class Program
{
static IConnectionFactory factory = new ConnectionFactory()
{
HostName = "192.168.100.2",
UserName = "uat",
Password = "137955aaA",
VirtualHost = "uat_vhost"
};
/// <summary>
/// 生产者
/// </summary>
public static void SendMessage()
{
//死信交换机
string dlxexChange = "dlx.exchange";
//死信队列
string dlxQueueName = "dlx.queue";
//消息交换机
string exchange = "direct.exchange";
//消息队列
string queueName = "direct.queue.delay";
using (var connection = factory.CreateConnection())
{
using (var channel = connection.CreateModel())
{
//创建死信交换机
channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建死信队列
channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false);
//死信队列绑定死信交换机
channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName);
// 创建消息交换机
channel.ExchangeDeclare(exchange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建消息队列,并指定死信队列
channel.QueueDeclare(queueName, durable: true, exclusive: false, autoDelete: false, arguments:
new Dictionary<string, object> {
{ "x-dead-letter-exchange",dlxexChange}, //设置当前队列的DLX(死信交换机)
{ "x-dead-letter-routing-key",dlxQueueName}, //设置DLX的路由key，DLX会根据该值去找到死信消息存放的队列
{ "x-message-ttl",3000}
});
//消息队列绑定消息交换机
channel.QueueBind(queueName, exchange, routingKey: queueName);
string message = "hello rabbitmq message";
var properties = channel.CreateBasicProperties();
properties.Persistent = true;
//发布消息
channel.BasicPublish(exchange: exchange,
routingKey: queueName,
basicProperties: properties,
body: Encoding.UTF8.GetBytes(message));
Console.WriteLine($"{DateTime.Now}队列:{queueName}发送消息:{message}");
}
}
}
/// <summary>
/// 消费延时队列
/// </summary>
public static void Consumer_delay()
{
//死信交换机
string dlxexChange = "dlx.exchange";
//死信队列
string dlxQueueName = "dlx.queue";
var connection = factory.CreateConnection();
{
//创建信道
var channel = connection.CreateModel();
{
//创建死信交换机
channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false);
//创建死信队列
channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false);
//死信队列绑定死信交换机
channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName);
var consumer = new EventingBasicConsumer(channel);
channel.BasicQos(prefetchSize: 0, prefetchCount: 1, global: true);
consumer.Received += (model, ea) =>
{
//处理业务
var message = Encoding.UTF8.GetString(ea.Body.ToArray());
Console.WriteLine($"{DateTime.Now}队列{dlxQueueName}消费消息:{message}");
channel.BasicAck(ea.DeliveryTag, false);
};
channel.BasicConsume(dlxQueueName, autoAck: false, consumer);
}
}
}
static void Main(string[] args)
{
Task.Factory.StartNew(() =>
{
for (int i = 0; i < 10; i++)
{
SendMessage();
System.Threading.Thread.Sleep(1000);
}
});
Consumer_delay();
Console.ReadLine();
}
}
延时队列（不同的过期时间）
延时队列处理，不同的过期时间的消息，会堵塞后面的消息，导致过期了还没消费。
可以通过rabbitmq_delayed_message_exchange 插件，解决这个问题。通过该插件，可以在 RabbitMQ 中实现延时消息投递和消费。
class Program
{
static IConnectionFactory factory = new ConnectionFactory()
{
HostName = "192.168.100.2",
UserName = "uat",
Password = "137955aaA",
VirtualHost = "uat_vhost"
};
/// <summary>
/// 生产者
/// </summary>
public static void SendMessage()
{
//延时交换机
string delayExchange = "dlx.exchange.delayed";
//延时队列
string delayQueueName = "dlx.queue.delayed";
using (var connection = factory.CreateConnection())
{
using (var channel = connection.CreateModel())
{
//创建延时交换机
channel.ExchangeDeclare(delayExchange, type: "x-delayed-message", durable: true, autoDelete: false, new Dictionary<string, object> {
{ "x-delayed-type","direct"}
});
//创建死信队列
channel.QueueDeclare(delayQueueName, durable: true, exclusive: false, autoDelete: false);
//死信队列绑定死信交换机
channel.QueueBind(delayQueueName, delayExchange, routingKey: delayQueueName);
string message = "hello rabbitmq message 10s后处理";
var properties = channel.CreateBasicProperties();
properties.Persistent = true;
properties.Headers = new Dictionary<string, object> { { "x-delay", "10000" } };
//发布消息
channel.BasicPublish(exchange: delayExchange,
routingKey: delayQueueName,
basicProperties: properties,
body: Encoding.UTF8.GetBytes(message));
Console.WriteLine($"{DateTime.Now}队列:{delayQueueName}发送消息:{message}");
message = "hello rabbitmq message 5s后处理";
properties = channel.CreateBasicProperties();
properties.Persistent = true;
properties.Headers = new Dictionary<string, object> { { "x-delay", "5000" } };
channel.BasicPublish(exchange: delayExchange,
routingKey: delayQueueName,
basicProperties: properties,
body: Encoding.UTF8.GetBytes(message));
Console.WriteLine($"{DateTime.Now}队列:{delayQueueName}发送消息:{message}");
}
}
}
/// <summary>
/// 消费延时队列
/// </summary>
public static void Consumer_delay()
{
//死信队列
string dlxQueueName = "dlx.queue.delayed";
var connection = factory.CreateConnection();
{
//创建信道
var channel = connection.CreateModel();
{
var consumer = new EventingBasicConsumer(channel);
channel.BasicQos(prefetchSize: 0, prefetchCount: 1, global: true);
consumer.Received += (model, ea) =>
{
//处理业务
var message = Encoding.UTF8.GetString(ea.Body.ToArray());
Console.WriteLine($"{DateTime.Now}队列{dlxQueueName}消费消息:{message}");
System.Threading.Thread.Sleep(20);
channel.BasicAck(ea.DeliveryTag, false);
};
channel.BasicConsume(dlxQueueName, autoAck: false, consumer);
}
}
}
static void Main(string[] args)
{
SendMessage();
Consumer_delay();
Console.ReadLine();
}
}
