No-acknowledge mode is a nonstandard extension to the JMS API. Normally, the broker waits for a client acknowledgment before considering that a message has been acknowledged and discarding it. That acknowledgment must be made programmatically if the client has specified client-acknowledge mode or it can be made automatically, by the session, if the client has specified auto-acknowledge or dups-OK-acknowledge. If a consuming client specifies no-acknowledge mode, the broker discards the message as soon as it has sent it to the consuming client. This feature is intended for use by nondurable subscribers consuming nonpersistent messages, but it can be used by any consumer.
Using this feature improves performance by reducing protocol traffic and broker work involved in acknowledging a message. This feature can also improve performance for brokers dealing with misbehaving clients who do not acknowledge messages and therefore tie down broker memory resources unnecessarily. Using this mode has no effect on producers.
You use this feature by specifying NO_ACKNOWLEDGE for the acknowledgeMode parameter to the createSession, createQueueSession, or createTopicSession method. No-acknowledge mode must be used only with the connection methods defined in the com.sun.messaging.jms package. Note however that the connection itself must be created using the javax.jms package.
The following are sample variable declarations for connection, queueConnection and topicConnection:
javax.jms.connection Connection; javax.jms.queueConnection queueConnection javax.jms.topicConnection topicConnection
The following are sample statements to create different kinds of no-acknowledge sessions:
//to create a no ack session Session noAckSession = ((com.sun.messaging.jms.Connection)connection) .createSession(com.sun.messaging.jms.Session.NO_ACKNOWLEDGE); // to create a no ack topic session TopicSession noAckTopicSession = ((com.sun.messaging.jms.TopicConnection) topicConnection) .createTopicSession(com.sun.messaging.jms.Session.NO_ACKNOWLEDGE); //to create a no ack queue session QueueSession noAckQueueSession = ((com.sun.messaging.jms.QueueConnection) queueConnection) .createQueueSession(com.sun.messaging.jms.Session.NO_ACKNOWLEDGE);
Specifying no-acknowledge mode for a session results in the following behavior:
The client runtime will throw a JMSException if Session.recover() is called.
The client runtime will ignore a call to the Message.acknowledge() method from a consumer.
Messages can be lost. As opposed to dups-OK-acknowledge, which can result in duplicate messages being sent, no-acknowledge mode bypasses checks and balances built into the system and may result in message loss.