These messages, which can either be
unstructured (raw) or structured (as Oracle objects, which are described in
Chapter 14), correspond to rows in a table. Messages are stored in normal queues for
normal message handling or in exception queues if they cannot be retrieved for some
reason.
Queue creation and management
Queues are created through PL/SQL commands or the Java API. An administrator
creates a queue by following these steps:
1. Create a queue table.
2. Create and name the queue.
3. Specify the queue as a normal queue or an exception queue.
4. Specify how long messages remain in the queue: indefinitely, for a fixed length of
time, until a particular time elapses between retries, or based on the number of
retries.
Queues can be started and stopped by the administrator, who also grants users the
privileges necessary for using the queue and revokes those privileges when necessary.
Producers of messages specify a queue name, enqueue options, message properties,
and the payload to be put into the queue, which is then handled by a producer agent.
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