13 Replies Latest reply on Jan 18, 2013 5:07 AM by ataylor

MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 1:56 PM

I'm starting here a discussion about: https://jira.jboss.org/jira/browse/HORNETQ-312

I believe it is legal to have MaxSession > 1 on MDB for durable subscriptions, right? We don't want MDBs to become singletons on durable subscriptions.

If a MDB is busy processing a message, another consumer can kick in and start processing the message in parallel.

It happens that HornetQMessageHandler had a check on number of consumers which is inconsistent with hornetQActivation, since it will start multiple Handlers for a given subscription:

for (int i = 0; i < spec.getMaxSessionInt(); i++)

{

ClientSession session = setupSession();

HornetQMessageHandler handler = new HornetQMessageHandler(this, session);

handler.setup();

session.start();

handlers.add(handler);

}

Hence, MDBs will always throw this following exception, unless you make maxSession = 1:

// Already exists

if (subResponse.getConsumerCount() > 0)

{

throw new javax.jms.IllegalStateException("Cannot create a subscriber on the durable subscription since it already has subscriber(s)");

}

1. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 1:58 PM (in response to clebert.suconic)

I meant.. a MDB instance... you could have multiple handlers processing the subscription.
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2. Re: MaxSessionInt on MDBs in durable subscriptions

timfox Feb 26, 2010 1:58 PM (in response to clebert.suconic)

The check in HornetQMessageHandler seems redundant to me, since the check is already done in HornetQSession
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3. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 1:58 PM (in response to timfox)

I removed it.. then we're good?
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4. Re: MaxSessionInt on MDBs in durable subscriptions

timfox Feb 26, 2010 2:02 PM (in response to clebert.suconic)

Well.. surely it will still fail on the HornetQSession check?

Doesn't each handler create it's own consumer?

What's the cardinality between handlers and consumers?
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5. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 2:19 PM (in response to timfox)

From what I just saw on the implementation, each Handler will have its own consumer, but on the same session.

I'm not really sure how transactions would be handled here though. Each instance should be isolated transactionally... but I'm not sure how this is going to work since they all share the same session.

Maybe Andy would have some idea?
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6. Re: MaxSessionInt on MDBs in durable subscriptions

timfox Feb 26, 2010 2:22 PM (in response to clebert.suconic)

Well, if each handler has it's own consumer, it won't work, since, HornetQ does not allow more than one consumer on a durable subscription.

This is mandated by the JMS spec.
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7. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 2:30 PM (in response to timfox)

The resource adapter is using core sessions directly. So the check on HornetQSession is not being done.

It seems to me the check on the counters should be done in a different place. It should be possible to have multiple instances of an MDB, but you should only have a single MDB on the subscription.
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8. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 2:47 PM (in response to clebert.suconic)

That's probably a different subject, but it's not clear to me how the resource adapter is guaranteeing transactions with multiple instances of a MDB (or maxSessionInt). The delivery will happen on a single session over multiple consumers?
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9. Re: MaxSessionInt on MDBs in durable subscriptions

timfox Feb 26, 2010 2:49 PM (in response to clebert.suconic)

There should only be only one consumer per session created by the JCA adaptor.

I.e. it should be a 1-1 mapping.
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10. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 2:50 PM (in response to timfox)

right, I will debug it and make sure this is not happening.
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11. Re: MaxSessionInt on MDBs in durable subscriptions

clebert.suconic Feb 26, 2010 3:25 PM (in response to timfox)

Duh.. I was reading it wrongly :-) it is opening a new session properly.

I will move the check on the counters for before the activation (or do it only at the first instance). That way I will be able to have multiple instances for the MDB.
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12. Re: MaxSessionInt on MDBs in durable subscriptions

hitjain_83 Jan 18, 2013 3:56 AM (in response to clebert.suconic)

I was curious to understand and setup multiple instances of an MDB - Can you please provide me with some guidance. "That way I will be able to have multiple instances for the MDB."
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13. Re: MaxSessionInt on MDBs in durable subscriptions

ataylor Jan 18, 2013 5:07 AM (in response to hitjain_83)

you have hijcked some one elses thread plus this is the dev forum, if you have questions can you raise them in the user forum
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