Duplicated Binding in the same queue

[Jay Zhu]

Hi - 

Does AMQP allows to have duplicate bindings in the same queue? Do I need to check if the binding exists when try to make a new one? If it does allows duplicate bindings, what's the implication?

I noticed in the RMQ Mgmt Console there are duplicated bindings in the same queue, and I have no idea how they were created. Does someone have any insight? I am on RMQ 3.2.4. The following is a snippet of the bindings in the exported JSON:

  "bindings": [
   ...

    {

      "source": "eventSource",

      "vhost": "/",

      "destination": "7b910e1e-e763-4f00-8042-0cd6fc5e5d86",

      "destination_type": "queue",

      "routing_key": "TestEvent",

      "arguments": {

        "eventEchoBack": true,

        "eventPattern": "TestEvent",

        "eventTTL": 3600

      }

    },

    {

      "source": "eventSource",

      "vhost": "/",

      "destination": "7b910e1e-e763-4f00-8042-0cd6fc5e5d86",

      "destination_type": "queue",

      "routing_key": "TestEvent",

      "arguments": {

        "eventEchoBack": true,

        "eventPattern": "TestEvent",

        "eventTTL": 3600

      }
   ...
  ]

Thanks,

Jay

[Michael Klishin]

On 26 August 2014 at 20:48:28, Jay Zhu (tingj...@gmail.com) wrote:
> Does AMQP allows to have duplicate bindings in the same queue? 

Yes, just try it.

> Do I need to check if the binding exists when try to make a new one?
> If it does allows duplicate bindings, what's the implication?

All declare and bind operations are idempotent. If you bind A to B
with the same routing key, nothing changes if the same binding exists.
If the routing key is different, another binding is added to the table.

In the end, a single message can be routed to a queue only once. 
--
MK

Staff Software Engineer, Pivotal/RabbitMQ

[Jason McIntosh]

Just an example I tested for this to explain just how restricted this is:  If you publish to a fanout exchange bound to two exchanges each of which is bound to the same queue, e.g. "MyBroadCastExchange" to "ExchangeA" and "ExchangeB" which are both fanouts to "MyQueue" - you'll still only get ONE message in the queue, even though ExchangeA and ExchangeB both "get a copy" of the message.  Seems a little strange to me, but I understand why that might actually be the case - both exchanges don't really get a copy of the message, they get I think an index id that correlates to the message, so you can't get duplicate messages in a queue.  At least I don't see any way to duplicate a message to a queue off hand

Jason

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[Jay Zhu]

Thank you for the info Michael! Won't it make sense for RMQ to avoid duplicated binding been created between the same exchange and queue?

Thanks,

Jay

[Jay Zhu]

Thanks Jason.  I think same binding between 2 Exchanges to the same Queue makes sense. However duplicated bindings between the same exchange to the same queue doesn't. I would consider that as a bug in RMQ.

Thanks,

Jay

[Michael Klishin]

 Jay Zhu (tingj...@gmail.com) wrote:
> > However duplicated bindings between the same exchange to the

> same queue doesn't. I would consider that as a bug in RabbitMQ.

Do you have a script that reproduces the problem? We'd be happy
to investigate.