[rabbitmq-discuss] Lose messages between restarts of broker

Thu Oct 28 19:50:43 BST 2010

> If you really need messages to go safely to disk, then you should put
> the channel into transactional mode (tx.select), and issue a tx.commit

What about unacknowledged messages? 

A Producer (rabbit 2.1.1 java client, not Spring Rabbit AMQP) commits some persistent messages on a durable queue/exchange. 

The Consumer is neither ack'ing nor rejecting the message to leave it on the queue (and let recovery retry it later), but I am committing periodically, e.g.:

  QueueingConsumer.Delivery delivery = consumer.nextDelivery();
  // neither channel.basicReject or Ack
  channel.txCommit();

Per ctl:

  $ rabbitmqctl list_queues name messages messages_unacknowledged messages_ready
  Listing queues ...
  testQueue       5       5       0

Using a soft "rabbitmqctl stop", a Broker restart will make the unacknowledged messages ready again (as expected). 
  testQueue       5       0       5

With a Broker hardkill, the unack'd messages disappear.
  testQueue       0       0       0

For our implementation, I was going to rely on unacknowledged messages, flow control (qos) and periodic channel.basicRecover() to implement a crude, controlled "delayed retry" behavior, without using a temporary parking queue or application-provided intermediate storage. Not that anyone would kill the broker but is there a way to flush unack'd messages to disk?

Thanks
-Rudi

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