Advanced Queuing - Oracle

Retry with Delay Interval
Dequeue Features
Visual Basic (OO4O): Example Code
OO4O supports asynchronous dequeuing of messages. First, the monitor is started
for a particular queue. When messages that fulfil the user criteria are dequeued, the
user's callback object is notified.
Java (JDBC): Example Code
AQDequeueOption deq-opt;
deq-opt = new AQDequeueOption ();
If the transaction dequeuing the message from a queue fails, it is regarded as an
unsuccessful attempt to consume the message. AQ records the number of failed
attempts to consume the message in the message history. Applications can query
the retry_count column of the queue table view to find out the number of
unsuccessful attempts on a message. In addition, AQ allows the application to
specify, at the queue level, the maximum number of retries for messages in the
queue. If the number of failed attempts to remove a message exceeds this number,
the message is moved to the exception queue and is no longer available to
applications.
Retry Delay
A bad condition can cause the transaction receiving a message to end. AQ allows
users to hide the bad message for a prespecified interval. A retry_delay can be
specified along with maximum retries. This means that a message that has had a
failed attempt will be visible in the queue for dequeue after the retry_delay interval.
Until then it will be in the WAITING state. In the AQ background process, the time
manager enforces the retry delay property. The default value for maximum retries is
5. The default value for retry delay is 0. Note that maximum retries and retry delay
are not available with 8.0-compatible multiconsumer queues.
PL/SQL (DBMS_AQADM Package): Example Code
/* Create a package that enqueue with delay set to one day: /*
CONNECT BOLADM/BOLADM
>
/* queue has max retries = 4 and retry delay = 12 hours */
execute dbms_aqadm.alter_queue(queue_name = 'WS.WS_BOOKED_ORDERS_QUE',
max_retr
ies=4,
retry_delay = 3600*12);
A Sample Application Using AQ 8-77