Advanced Queuing - Oracle

Enqueue Features
cannot have the same values for the NAME, ADDRESS and PROTOCOL attributes for
the AQ$_AGENT type. At least one of the three attributes must be different for two
subscribers (see "Agent Type (aq$_agent)" on page 2-3 for formal description of this
data structure).
You cannot add subscriptions to single-consumer queues or exception queues. A
consumer that is added as a subscriber to a queue will only be able to dequeue
messages that are enqueued after the DBMS_AQADM.ADD_SUBSCRIBER procedure
is completed. In other words, messages that had been enqueued before this
procedure is executed will not be available for dequeue by this consumer.
You can remove a subscription by using the DBMS_AQADM.REMOVE_SUBSCRIBER
procedure (see "Removing a Subscriber" in Chapter 9, "Administrative Interface").
AQ will automatically remove from the queue all data corresponding to the
consumer identified by the AQ$_AGENT parameter. In other words, it is not an error
to execute the REMOVE_SUBSCRIBER procedure even when there are pending
messages that are available for dequeue by the consumer. These messages will be
automatically made unavailable for dequeue after the REMOVE_SUBSCRIBER
procedure is executed. In a queue table that is created with the compatible
parameter set to '8.1' or higher, such messages that were not dequeued by the
consumer will be shown as "UNDELIVERABLE" in the AQ$ view.
Note that a multiconsumer queue table created without the compatible parameter,
or with the compatible parameter set to '8.0', does not display the state of a message
on a consumer basis, but only displays the global state of the message.
Recipient Lists
You do not need to specify subscriptions for a multiconsumer queue if the
producers of messages for enqueue supply a recipient list of consumers. In some
situations it may be desirable to enqueue a message that is targeted to a specific set
of consumers rather than the default list of subscribers. You accomplish this by
specifying a recipient list at the time of enqueuing the message.
In PL/SQL you specify the recipient list by adding elements to the
recipient_list field of the message_properties record.
In OCI the recipient list is specified by using the LNOCISetAttr procedure to
specify an array of LNOCI_DTYPE_AQAGENT descriptors as the recipient list
(LNOCI_ATTR_RECIPIENT_LIST attribute) of an LNOCI_DTYPE_AQMSG_
PROPERTIES message properties descriptor.
If a recipient list is specified during enqueue, it overrides the subscription list. In
other words, messages that have a specified recipient list will not be available for
dequeue by the subscribers of the queue. The consumers specified in the recipient
A Sample Application Using AQ 8-37