[rabbitmq-discuss] Duplicated message and unknown delivery tag after ack

[Lukasz Olczak]

Hi,

I have RabbitMQ 3.1.1, Erlang R16B deployed on my laptop and a collection 
of consumers consuming messages from single queue through loopback 
interface. Consumers are written in Java (I use a spring-rabbit 1.1.1 
library) and every consumer uses a distinct thread. 
During a heavy load very strange errors occurred. Some messages were 
duplicated and delivered to two consumers in the same time (in the same 
second). Both consumers after a processing acknowledged the message and 
then one of them received shutdown signal with an error message: 
com.rabbitmq.client.ShutdownSignalException: channel error; reason: 
{#method<channel.close>(reply-code=406, reply-text=PRECONDITION_FAILED - 
unknown delivery tag 1, class-id=60, method-id=80), null, ""}
Every thread uses a distinct channel. So, single message is delivered and 
acknowledged in the same channel.
I reviewed the whole code both mine and spring and didn't find any bug.

Anybody knows why RabbitMQ duplicates messages on a single broker with a 
publisher and consumers connected through loopback interface?
How can I handle it? or where did I make a mistake?  

Thanks in advance.

Regards
Lukasz 
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