Advanced Queuing - Oracle

General Questions
(you must have the AQ background process running for this to happen). You can
dequeue these messages from the exception queue with a normal dequeue.
Is it possible to update the message payload after it has been
enqueued?
Only by dequeuing and enqueuing the message again. If you are changing the
message payload, it is a different message.
Can asynchronous notification be used to invoke an executable every
time there is a new message?
Notification is possible only to OCI clients. The client does not have to be connected
to the database to receive notifications. The client specifies a callback function
which will be executed for each message. Asynchronous Notification cannot be
used to invoke an executable, but it is possible for the callback function to invoke a
stored procedure.
Does propagation work from multiconsumer queues to single-consumer
queues and vice versa?
Propagation from a multiconsumer queue to a single consumer queue is possible.
The reverse is not possible (propagation is not possible from a single consumer
queue).
Why do I sometimes get ORA-1555 error on dequeue?
You are probably using the NEXT_MESSAGE navigation option for dequeue. This
uses the snapshot created during the first dequeue call. After that the other dequeue
calls generate more undo which fills up the rollback segment and hence generates
1555.
The workaround is to use the FIRST_MESSAGE option to dequeue the message.
This will reexecute the cursor and get a new snapshot. This might not perform as
well, so we suggest you dequeue them in batches: FIRST_MESSAGE for one, and
NEXT_MESSAGE for the next, say, 1000 messages, and then FIRST_MESSAGE again,
and so on.
What are the different subscriber types recorded on the subscriber
table?
The subscriber_types and their values are:
1 - Current Subscriber. The subscribers name, address and protocol are in the same
row.
6-4 Oracle9i Application Developer’s Guide - Advanced Queuing