redelivery is handled by the consumer, so client side. messages pending redelivery are seen as inflight by the broker and not available to other consumers. It is possible to break the order constraint and receive messages backed up behind a message pending redelivery, but this is all local to the client consumer.
When redelivery is exhausted, the message is returned to the broker with a poison ack, which the broker responds by removing the message and doing Dead letter queue processing (DLQ).
This enhancement will allow a replacement of DLQ handling that will handle redelivery. It is based on the ideas outlined and implemented by a camel route in https://issues.apache.org/jira/browse/AMQ-2710
The idea is a BrokerPlugin will override sendToDeadLetterQueue and resend the message to the original destination in accordance with a matching RedeliveryPolicy. The resend will use the broker schedular to implement the delayed send after the message has been acked as poison by the consumer.
So the message will essentially be enqueued at the tail of the queue and dispatched again to any available consumer.
If retries are exceeded or there is no matching redelivery policy for a destination, normal DLQ processing will take place.
This will work in conjunction with consumer/client redelivery exhaustion or using a redelivery policy in the url query of jms.redeliveryPolicy.maximumRedeliveries=0