Advanced Queuing - Oracle

end;
Nonpersistent Queues
END LOOP;
General Features of Advanced Queuing
A message in a nonpersistent queue is not stored in a database table. You create a
nonpersistent queue, which can be either a single-consumer or multiconsumer type.
These queues are created in a system-created queue table (AQ$_MEM_SC for
single-consumer queues and AQ$_MEM_MC for multiconsumer queues) in the
schema specified by the create_np_queue command. Subscribers can be added
to the multiconsumer queues (see "Creating a Nonpersistent Queue" on page 9-26).
Nonpersistent queues can be destinations for propagation.
You use the enqueue interface to enqueue messages into a nonpersistent queue in
the normal way. You can enqueue RAW and Object Type (ADT) messages into a
nonpersistent queue. You retrieve messages from a nonpersistent queue through the
asynchronous notification mechanism, registering for the notification (using
LNOCISubcriptionRegister or DBMS_AQADM.REGISTER) for the queues you
are interested in (see "Registering for Notification" on page 11-55).
When a message is enqueued into a queue, it is delivered to clients with active
registrations for the queue. The messages are published to the interested clients
without incurring the overhead of storing them in the database.
See Also: Documentation on DBMS_AQADM.REGISTER in
Oracle9i Supplied PL/SQL Packages and Types Reference and
documentation on LNOCISubscriptionRegister in Oracle Call
Interface Programmer’s Guide.
Scenario
Assume that there are three application processes servicing user requests at the
Order Entry system. The connection dispatcher shares out connection requests from
the application processes. It attempts to maintain a count of the number of users
logged on to the Order Entry system and the number of users for each application
process. The application processes are named APP_1, APP_2, APP_3. (Application
process failures are not considered in this example.)
Using nonpersistent queues meets the requirements in this scenario. When a user
logs on to the database, the application process enqueues to the multiconsumer
nonpersistent queue, LOGIN_LOGOUT, with the application name as the consumer
name. The same process occurs when a user logs out. To distinguish between the
A Sample Application Using AQ 8-17