max-delivery-attempts does not work for un-acknowledged messages

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I noted strange behavior in Artemins. I'm not sure if this is a bug or if I don't understand something. I use Artemis Core API. I set autoCommitAcks to false. I noted that If message is received in MessageHandler but message is not acknowledged and session is rollbacked then Artemis does not consider this message as undelivered, Artemis consider this message as not sent to consumer at all. Parameter max-delivery-attempts does not work in this case. Message is redelivered an infinite number of times. Method org.apache.activemq.artemis.api.core.client.ClientMessage#getDeliveryCount returns 1 each time. Message has false value in Redelivered column in web console. If message is acknowledged before session rollback then max-delivery-attempts works properly.

What exactly is the purpose of message acknowledge? Acknowledge means only that message was received or acknowledge means that message was received and processed successfully? Maybe I can use acknowledge in both ways and it only depends on my requirements?

By message acknowledge I mean calling org.apache.activemq.artemis.api.core.client.ClientMessage#acknowledge method.

activemq-artemis
1 Answers

The behavior you're seeing is expected.

Core clients actually consume messages from a local buffer which is filled with messages from the broker asynchronously. The amount of message data in this local buffer is controlled by the consumerWindowSize set on the client's URL. The broker may dispatch many thousands of messages to various clients that sit in these local buffers and are never actually seen in any capacity by the consumers. These messages are considered to be in delivery and are not available to other clients, but they are not considered to be delivered. Only when a message is acknowledged is it considered to be delivered to a client.

If the client is auto-committing acknowledgements then acknowledging a message will quickly remove it from its respective queue. Once the message is removed from the queue it can no longer be redelivered because it doesn't exist anymore on the broker. In short, you can't get configurable redelivery semantics if you auto-commit acknowledgements.

However, if the client is not auto-committing acknowledgements and the consumer closes (for any reason) without committing the acknowledgements or calls rollback() on its ClientSession then the acknowledged messages will be redelivered according to the configured redelivery semantics (including max-delivery-attempts).

user_83819460
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