rabbitmq 复习

[wangduanduan]

基本概念

• 生产者：负责产生消息，并发送消息
• 队列：多个生产者可以把消息投放到同一个队列，多个消费者也可以从队列中读取消息
• 消费者：消费者负责从队列中接收消息

工作队列

• 一个woker处理某个消息，另一个就不会受到这个消息
• rabbitmq使用轮转的方式将消息发给worker。例如第一个消息发给worker1, 第二个消息就会发给worker2, 第三个消息再发给work1

队列durable和消息persistent的区别？

• 队列durable表示rabitmq重启后，队列中的消息不会丢失
• 消息persistent并不能保证消息并不丢失，只是告诉RabbitMq要把消息写到磁盘，但是消息到磁盘之前，还要经过缓存，如果在缓存这一步丢失，mq重启后，消息将会丢失。

// 队列durable
ch.assertQueue('hello', {durable: true});

// 消息persistent
ch.sendToQueue(q, new Buffer(msg), {persistent: true});

Marking messages as persistent doesn't fully guarantee that a message won't be lost. Although it tells RabbitMQ to save the message to disk, there is still a short time window when RabbitMQ has accepted a message and hasn't saved it yet. Also, RabbitMQ doesn't do fsync(2) for every message -- it may be just saved to cache and not really written to the disk. The persistence guarantees aren't strong, but it's more than enough for our simple task queue. If you need a stronger guarantee then you can use

prefetch

perfetch用来设置，如果一个消息还没有被消费者处理完并确认，就不要再给这个消息发送消息

ch.prefetch(1);

推送订阅

工作队列，每个消息只能被一个消费者消费。而推送订阅方式，一个消息可以被多个消费者消费。

The core idea in the messaging model in RabbitMQ is that the producer never sends any messages directly to a queue. Instead, the producer can only send messages to an exchange. There are a few exchange types available: - direct, topic, headers and fanout

// 声明exchange
ch.assertExchange('logs', 'fanout', {durable: false})

临时队列

• 队列名由Rabbitmq产生
• 消费者断开连接，队列自动删除
• 每次连接成功后，该队列中都没有任何老的消息

// 队列名为空字符串，就是临时队列
channel.assertQueue('', {
  exclusive: true
});

队列

• 参考详情：https://www.rabbitmq.com/queues.html 队列名
• Queue names may be up to 255 bytes of UTF-8 characters.
• 不允许以"amq."开头, 否则报错403

队列属性

• Name
• Durable (the queue will survive a broker restart)
• Exclusive (used by only one connection and the queue will be deleted when that connection closes)
• Auto-delete (queue that has had at least one consumer is deleted when last consumer unsubscribes)
• Arguments (optional; used by plugins and broker-specific features such as message TTL, queue length limit, etc)

队列声明

1. 如果要声明的队列不存在，则创建
2. 如果要声明的队列存在，则检查传递的队列属性和已经存在的队列的属性是否相同，如果相同，则使用已经存在的队列。如果不同，则会报错406 PRECONDITION_FAILED

exchange

• direct : a message goes to the queues whose binding key exactly matches the routing key of the message.
• topic
• headers
• fanout

其他

RabbitMQ doesn't allow you to redefine an existing queue with different parameters and will return an error to any program that tries to do that.

参考

• https://www.rabbitmq.com/tutorials/amqp-concepts.html