Advanced Queuing - Oracle

Enqueue Features
list may or may not be subscribers for the queue. It is an error if the queue does not
have any subscribers and the enqueue does not specify a recipient list (see
"Enqueuing a Message" on page 11-4 in Chapter 11, "Operational Interface: Basic
Operations").
Priority and Ordering of Messages
The message ordering dictates the order that messages are dequeued from a queue.
The ordering method for a queue is specified when a queue table is created (see
"Creating a Queue Table" on page 9-4 in Chapter 9, "Administrative Interface").
Priority ordering of messages is achieved by specifying priority, enqueue time as
the sort order for the message. If priority ordering is chosen, each message will be
assigned a priority at enqueue time by the enqueuer. At dequeue time, the messages
will be dequeued in the order of the priorities assigned. If two messages have the
same priority, the order in which they are dequeued is determined by the enqueue
time. A first-in, first-out (FIFO) priority queue can also be created by specifying the
enqueue time, priority as the sort order of the messages.
Scenario
In the BooksOnLine application, a customer can request:
FedEx shipping (priority 1),
Priority air shipping (priority 2). or
Regular ground shipping (priority 3).
The Order Entry application uses a priority queue to store booked orders. Booked
orders are propagated to the regional booked orders queues. At each region, orders
in these regional booked orders queues are processed in the order of the shipping
priorities.
The following calls create the priority queues for the Order Entry application.
PL/SQL (DBMS_AQADM Package): Example Code
/* Create a priority queue table for OE: */
EXECUTE dbms_aqadm.create_queue_table( \
queue_table => 'OE_orders_pr_mqtab', \
sort_list =>'priority,enq_time', \
comment => 'Order Entry Priority \
multiple_consumers
MultiConsumer Orders queue table',\
=> TRUE, \
queue_payload_type => 'BOLADM.order_typ', \
8-38 Oracle9i Application Developer’s Guide - Advanced Queuing