Cycling deadletter behavior

[nicolas esclapez]

Hi, 

I am working on a base RabbitMQ app where messages can't be loose.

All incoming messages must be Validate, Cancelled for retry later (noAck) or definitely rejected (moved to a trash queue)

The configuration : 

I have 2 exchanges : 'secondary.direct', 'cancel.fanout' and 2 queues : 'ProductBaseCheck.0' and '_delayed' with a TTL value

The binding :

- secondary.direct --> ProductBaseCheck.0 (with rootkey)

- cancel.fanout --> _delayed

Each queue have a dead letter exchange :

- ProductBaseCheck.0 (DLX)--> cancel.fanout

- _delayed (DLX)--> secondary.direct

Case 1 :

- A message is published on secondary.direct --> it is moved to the ProductBaseCheck.0 queue 

- The ttl expires -->  it is moved to _delayed queue

- The ttl expires again --> the message is detroyed by Rabbit MQ (see log below)

> =WARNING REPORT==== 5-Oct-2016::18:36:56 ===

Message dropped. Dead-letter queues cycle detected: [<<"ProductBaseCheck.0">>,

>                                                      <<"_delayed">>,

>                                                      <<"ProductBaseCheck.0">>]

> This cycle will NOT be reported again.

Case 2 :

- A message is published on secondary.direct --> it is moved to the ProductBaseCheck.0 queue and waiting for consume

- The consumer cancel the message (noack) --> it is moved to _delayed queue

- The ttl expires --> the message is move to the ProductBaseCheck.0 queue and can cycle indefinitely (see the message dump below, after many cycles)

Exchange secondary.direct

Routing Key ProductBaseCheck.0

Redelivered ?

Properties

..timestamp: 1475691989728

..priority: 0

..delivery_mode: 2

..headers:

....item-retry-count: 0

....x-death: count: 6

....exchange: cancel.fanout

....queue: _delayed

....reason: expired

....routing-keys: ProductBaseCheck.0

....time: 1475684807

count: 1

reason: rejected

queue: ProductBaseCheck.0

time: 1475684792

exchange: primary.fanout

routing-keys: ProductBaseCheck.0

count: 5

exchange: secondary.direct

queue: ProductBaseCheck.0

reason: expired

routing-keys: ProductBaseCheck.0

time: 1475684837

content_type: text/plain; charset=utf-8

Payload 32 bytes Encoding: string {"Id":12,"Name":"toBeCancelled"}

Questions :

- It is possible to disabled cycle detection (case 1) ?

- Is the cycling behavior (case 2) will be fixed on a future version ?

Thanks

Best Regards

Nicolas Esclapez

[Michael Klishin]

You cannot disable cycle checking and it uses pairs of {queue, dead-lettering reason} to identify unique events.

So if it is dead-lettered for two different reasons, they are not counted as the same thing. Other than that we are not aware of

any cases when cycle detection does not work as expected.

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MK

Staff Software Engineer, Pivotal/RabbitMQ