Advanced Queuing - Oracle

Enqueue Features
feature applied in the context of the BooksOnLine scenario, refer to "Elements of
Advanced Queuing" on page 1-21.
Priority and Ordering of Messages in Enqueuing
Message Grouping
Propagation
It is possible to specify the priority of the enqueued message. An enqueued message
can also have its exact position in the queue specified. This means that users have
three options to specify the order in which messages are consumed: (a) a sort order
specifies which properties are used to order all message in a queue; (b) a priority
can be assigned to each message; (c) a sequence deviation allows you to position a
message in relation to other messages. Further, if several consumers act on the same
queue, a consumer will get the first message that is available for immediate
consumption. A message that is in the process of being consumed by another
consumer will be skipped.
To see this feature applied in the context of the BooksOnLine scenario, refer to
"Priority and Ordering of Messages" on page 8-38.
Messages belonging to one queue can be grouped to form a set that can only be
consumed by one user at a time. This requires that the queue be created in a queue
table that is enabled for message grouping. All messages belonging to a group have
to be created in the same transaction and all messages created in one transaction
belong to the same group. This feature allows users to segment complex messages
into simple messages; for example, messages directed to a queue containing
invoices can be constructed as a group of messages starting with the header
message, followed by messages representing details, followed by the trailer
message.
To see this feature applied in the context of the BooksOnLine scenario, refer to
"Message Grouping" on page 8-51.
This feature enables applications to communicate with each other without having to
be connected to the same database or the same queue. Messages can be propagated
from one Oracle AQ to another, irrespective of whether the queues are local or
remote. Propagation is done using database links and Oracle Net Services.
To see this feature applied in the context of the BooksOnLine scenario, refer to
"Propagation" on page 8-107.
1-16 Oracle9i Application Developer’s Guide - Advanced Queuing