Limit number of concurrent MDBs and number of retries?

[kenrod]

Dear All,

I am finding when I set up a Queue much like the example at...

http://trailblazer.demo.jboss.com/EJB3Trail/serviceobjects/mdb/

...JBoss instantiates several (I'm guessing around 5) consumers that all hungrily grab whatever appears on the Queue in a concurrent fashion. Also, if any of the message processing fails, they retry several (I'm guessing around 10) times before assigning the message to the DLQ.

My question is: how can I control this behaviour?

My requirement is for a sequential, single-threaded point-to-point, so all I want is one consumer that processes each message just once. If the message fails to consume then so be it: as long as it reached the consumer I'm happy.

I have tried setting the ActivationConfigProperties maxSessions to 1, DLQMaxResent to 1, and transacted to false, as listed at...

http://wiki.jboss.org/wiki/Wiki.jsp?page=ConfigJMSMessageListener

...but they all seem to have little effect?

You help is most appreciated,

Richard.

[kenrod]

If it helps, this page...

http://wiki.jboss.org/wiki/Wiki.jsp?page=ConfigJBossMDB

...seems to be exactly what I want, with its mention of MaxmimumSize and MaxTimesRedelivered, but how do I configure this in my EJB3 environment?

[peter_kaas]

We use:

@MessageDriven(activationConfig = {
 @ActivationConfigProperty(
 propertyName = "destinationType",
 propertyValue = "javax.jms.Queue"
 ),
 @ActivationConfigProperty(
 propertyName = "destination",
 propertyValue = "queue/trigger/Stage1EventBatchQueue"
 ),
 @ActivationConfigProperty(
 propertyName = "minPoolSize",
 propertyValue = "1"
 ),
 @ActivationConfigProperty(
 propertyName = "maxPoolSize",
 propertyValue = "1"
 )
})

in our code. I think the minPoolSize and maxPoolSize are what you are looking for (that works for us).

As for getting a message just once: just make sure your MDB doesn't throw any exceptions by catching Throwable at the top of your onMessage()?

[kenrod]

Peter,

Fantastic! I will give that a try - it sounds like exactly what I need!

With regards to catching Exceptions, that one is more tricky: I do catch Exceptions at the top level of my onMessage (and don't rethrow them), but the message still gets re-delivered.

Looking at the stack trace of the Exception that I catch, there's a lot of references to jboss.aop in there, so I fear JBoss may be detecting the Exception and rolling back even though I am catching it.

Is there a parameter to limit the number of retries?

Regards,

Richard.

[kenrod]

For those travelling this way themselves, I found that using...

void onMessage( Message p_message )
{
 if ( p_message.getJMSRedelivered()) return;
 ...

...is a (slightly yucky) way of avoiding the resends. Of course, an ActivationConfigProperty would be better...

[jsb]

Came across this old topic looking for the answer to the same question... The ActivationConfigProperty that works for me with EJB3rc8 is:

@ActivationConfigProperty(propertyName = "DLQMaxTimesRedelivered", propertyValue = "0")