The default is AUTO_ACKNOWLEDGE, where the system automatically acknowledges a message once the consumer has processed it. This mode guarantees at most one redelivered message after a provider failure.
In the AUTO_ACKNOWLEDGE mode, the session automatically acknowledges each message consumed by the client. The session thread blocks, waiting for the broker to confirm that it has processed the client acknowledgement for each consumed message.
If a session is closed without the client acknowledging the message or if the message broker fails before the acknowledgment is processed, the broker redelivers that message, setting a JMSRedelivered flag.
When the transaction mode is set to XA, the JMS session becomes part of the existing transaction, and is processed according to the XA two-phase commit protocol. In the first phase, the resource manager sends a query to commit to the receivers and waits for the receivers to respond with a confirmation. In the second phase, the resource manager receives confirmation from all receivers, and commits the message to all receivers. This setting prevents message loss and duplicate messages, even when a system unexpectedly shuts down.
|
Manesh is a Sr. EAI Consultant, at present working in Singapore (Little Red Dot). 
