Performance of AQ when using callback procedure (using PL/SQL notification)

Question

I am enqueueing XMLType in AQ.XML file is large in size.NOw I want to dequeue the AQ using PL/SQL notification(using callback procedure which will call DBMS_AQ.DEQUEUE to dequeue the AQ and process the XML.After fetching the data from XML ,I want to store these data in another table columns).
Please suggest,In this case which approach would be better to dequeue the AQ table :
1.PL/SQL notification(using callback procedure)
OR
2.Scheduling the call to DBMS_AQ.DEQUEUE to dequeue the AQ table
What would be the impact on performance of above two approaches?

Answer 1

Hi,
The question of performance is not down to the technique one employes to enqueue/dequeue, but at a basic level, is relative to the number of messages!
The is what the Oracle documentation states:
>
When persistent messages are enqueued, they are stored in database tables. The performance characteristics of queue operations on persistent messages are similar to underlying database operations. The code path of an enqueue operation is comparable to SELECT and INSERT into a multicolumn queue table with three index-organized tables. The code path of a dequeue operation is comparable to SELECT, DELETE, and UPDATE operations on similar tables.
>
So, if anything, the dequeue is a fraction more time & resource consuming. However, it is only a "fraction". You could always add multiple subscribers to dequeue if you want!
You could ofcourse choose to have non-persistent messages if your application does not need the kind of fault-tolerance that persistent messaging offers, which speed things up, but only a bit, so don't get too excited about it!
There are other things to consider however, which you may wish to read up on before getting bogged down on whether you should use notification or the scheduler:
- Is your system clustered?
- Concurrency on a single queue (i.e. multiple enqueues/dequeues, but single queue)
- Propogation latency issues
Read about these and much more at:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14257/perform.htm
Finally, whether you pl/sql notification or not and whether you use dbms_scheduler is down to your application requirements!
P;