Consume multiple queues in python / pika
Question: I am trying to create a consumer that would subscribe to multiple queues, and
then process messages as they arrive.

The problem is that when there is some data already present in the first
queue, it consumes the first queue and never goes to consume the second queue.
However, when the first queue is empty, it does go to the next queue, and then
consumes both queues simultaneously.

I had first implemented threading but want to steer clear of it, when pika
library does it for me without much complexity. Below is my code:

    
    
    import pika
    
    mq_connection = pika.BlockingConnection(pika.ConnectionParameters('x.x.x.x'))
    mq_channel = mq_connection.channel()
    mq_channel.basic_qos(prefetch_count=1)
    
    
    def callback(ch, method, properties, body):
        print body
        mq_channel.basic_ack(delivery_tag=method.delivery_tag)
    
    mq_channel.basic_consume(callback, queue='queue1', consumer_tag="ctag1.0")
    mq_channel.basic_consume(callback, queue='queue2', consumer_tag="ctag2.0")
    mq_channel.start_consuming()
    


Answer: The issue is most likely that the first call has issued a Basic.Consume and
has already received messages from a pre-populated queue before the second
call is issued. You might want to try setting the QoS prefetch count to 1,
which will limit RabbitMQ from sending you more than one message at a time.

