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

Emile Joubert emile at rabbitmq.com
Thu Aug 1 10:46:37 BST 2013

Hi Lukasz,

On 31/07/13 17:30, Lukasz Olczak wrote:
> 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, ""}

There are legitimate ways in which multiple consumers could get hold of
the same message, in the same second. If any consumer rejects a message
or reconnects then unacknowledged messages will be returned to the
broker and may be delivered to other consumers. Such messages will have
the redelivered flag set.

The error you quote could also arise if an application acknowledges
messages incorrectly. Make sure that messages are only acknowledged once.

> Anybody knows why RabbitMQ duplicates messages on a single broker with a
> publisher and consumers connected through loopback interface?

This is unlikely to have anything to do with the loopback interface
directly. Though loopback offers greater speed which may expose race

If you believe there is a broker error then please run your test via the
Tracer protocol analyser and send us the generated trace file:


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