MQSeries.net :: View topic - Priority queue message order problem in WAS MDB

bennytseng · Posted: Tue Jun 13, 2006 6:22 pm Post subject:

Got a problem with the MDB message reading order under WAS 5.1. Wonder if anyone can shed some light.

The environment:
1. WebSphere Application Server v5.1.
2. WebSphere MQ v5.3
3. Created local queue with the property "Message Delivery Sequence" set to "Priority".
4. Created the necessary WebSphere MQ JMS Provider resources including the queue connection factory and queue destination.
5. For the queue destination resource, I left the "Priority" setting to "Application Defined", since my application programatically set the message priority.
5. Created a message listener port for the MDB listening on the queue.

My Java application creates two threads, one thread generating message at high priority (7) and the other one generating message at low pririty (3). The threads are long running and keep pumping out messages at regular intervals.

Now, my MDB is able to receive messages from the queue. However, the listener service is pulling messages off in the opposite order implied by the message priority. By examining my application output and monitoring through MQ explorer, I confirmed that it's the high priority messages that get stuck on the queue while the low priority messages are processed as fast as possible.

To confirm the problem is indeed related to the MDB, I wrote a simple Java application that including a loop doing blocking MQGET on the queue. This application works as expected, high prioirty messages get processed first.

Another thing I did is stopping the message listener port and then running my application, allowing the messages to be piled up on the queue. I then brought up the MQ explorer to examine the queue. All messages are placed in an order obeying the priority settings.

That makes me think that the MDB/message listener service is not processing according to the message priority.

I was able to examine the underlying MQ API calls made by the listener. It seems that the listener is using a sequence of MQGET with the MQGMO_BROWSE_FIRST/MQGMO_BROWSE_NEXT option. Looking up the MQ manual and I found the following:

If the queue has a MsgDeliverySequence of MQMDS_PRIORITY, and a message arrives on the queue that is of a higher priority than the one currently pointed to by the browse cursor, that message is not found during the current sweep of the queue using MQGMO_BROWSE_NEXT.
It can be found only after the browse cursor has been reset with MQGMO_BROWSE_FIRST (or by reopening the queue).

This seems to explain the problem I am seeing.

Has anyone hit a similar problem and/or tell me if this is a bug in WAS or a configuration/programming error on my side?

Thanks in advance.

Benny