Two subscriptions using a single durable queue

[laurentluce]

Messages don't seem to end up on the right subscription when I have two subscriptions using a single durable queue.

Here is my routing configuration:

• One topic exchange: app
• Two STOMP subscriptions against that exchange using the same durable queue "queue-test"
  • topic.a.*
  • topic.b.*

rabbitmqctl list_bindings:

• exchange queue-test queue queue-test []
• app exchange queue-test queue topic.a.* []
• app exchange queue-test queue topic.b.* []

rabbitmqctl list_consumers:

• queue-test rabbit@localhost.2.20427.0 T_sub.HNNZbjRINADxFbrp true 0 []
• queue-test rabbit@localhost.2.20427.0 T_sub.ApMOzTQPNUlvwhmj true 0 []

rabbitmqctl list_queues:

• queue-test 0

Message 1 with destination topic.a.1 sent. Message received on the right subscription:

MESSAGE
    subscription : sub.ApMOzTQPNUlvwhmj
    destination : /exchange/app/topic.a.1
    message-id : T_sub.ApMOzTQPNUlvwhmj@@session-uqt3ppLSTqUnYXQBPb4-6w@@1
    redelivered : false
    ack : T_sub.ApMOzTQPNUlvwhmj@@session-uqt3ppLSTqUnYXQBPb4-6w@@1

Message 2 with destination topic.a.1 sent. Message received on the wrong subscription:

MESSAGE
    subscription : sub.HNNZbjRINADxFbrp
    destination : /exchange/app/topic.a.1
    message-id : T_sub.HNNZbjRINADxFbrp@@session-uqt3ppLSTqUnYXQBPb4-6w@@2
    redelivered : false
    ack : T_sub.HNNZbjRINADxFbrp@@session-uqt3ppLSTqUnYXQBPb4-6w@@2

Both messages should have been received on the subscription: ApMOzTQPNUlvwhmj since both messages destination match topic.a. and not topic.b.

[michaelklishin]

According to what you posted, both messages have the same destination and two consumers use a single queue.

When two consumers share a queue, a case known as competing consumers, messages are distributed in the round robin manner. See tutorial two.

If you want both subscription to receive a copy, use a topic destination so that each has its own queue.

[michaelklishin]

In other words, message replication happens during the routing stage, not delivery. If you want N consumers to receive something, they must each have their own queue.

[laurentluce]

@michaelklishin I don't want each subscription to receive a copy. Each subscription above uses a different pattern: topic.a.* and topic.b.* I do use the same queue name when i send the STOMP subscribe commands. I was expecting messages to be received based on the subscriptions topic pattern. The message with destination /exchange/app/topic.a.1 should not be received by the subscription with pattern topic.b.* unless I am missing something.

[michaelklishin]

@laurentluce see above. The feature you are asking for is known as consumer selectors. It is not available in RabbitMQ. Message distribution happens at the routing stage. I don't have anything to add to the comments above.

[michaelklishin]

To be more precise, consumer selectors are implemented in the jms-topic-exchange plugin but it is JMS-specific and doesn't fit the semantics of STOMP.

[laurentluce]

@michaelklishin Thanks for clarifying. I understand now that I need to use two queues.