RabbitMQ 中如何将消息传递给消费者

Question

I am currently developing an application which uses RabbitMQ Message broker. I have a confusion on how the message delivery work and I already went through their official docs but could not clarify my concern.

Say my application can take messages from two queues, For the queue A, producer directly push messages to this queue and the queue B gets message via an exchange. My question is if there are messages coming from queue A and queue B at the same time to the consumer, how would the consumer consume these messages? Sequentially or by creating multiple parallel threads?.

And if my main thread is responsible for reading the message, will making the main thread go to sleep stops consuming messages from the queue? I mean will rabbitMQ stop pushing messages to the consumer as long as the main thread is a sleep? I am not using the consumer acks as of now and trying to see if message consuming can be stopped by making the main thread go to sleep for a desired amount of time.

Answer 1

A RabbitMQ consumer can only consume messages from a single queue. There are two mechanisms by which a RabbitMQ consumer consumes a message from the queue

1. Push mechanism - In this type, the rabbitmq-server takes the responsibility of pushing the message to the consumer, whenever there is a message in the queue. The number of messages to be sent to the consumer can be controlled using the basic_qos configuration. The message can be automatically acknowledged or can be acknowledged by the consumer.
2. Pull mechanism - In this type, it is the job of the consumer to request the rabbitmq-server for the message. Only one message can be requested at a time.

When a consumer connects using the push mechanism, the consumer runs an IO loop, so when you run a long-running job, there are chances that the long-running job can hinder the consumer heartbeat to the rabbitmq server. One way of handling this is to run the long-running job on a separate thread.