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From Chris Sears <cse...@gmail.com>
Subject Re: onMessage() always acknowledges msg even if Session is set to CLIENT_ACK
Date Wed, 09 Mar 2011 21:03:12 GMT
Hi Kim,

Just to add to Rajith's comments, it sounds like you may be trying to use
the ring queue, onMessage(), queue browsing and client acknowledgements in a
way they were not designed to work.

If you have multiple clients that all need to read the same message, the
message producer should be sending the messages to a topic exchange and not
a direct exchange. With a topic exchange, the producer sends messages to a
named topic just like a named queue, but the broker will delivery a copy of
each message to every client who is subscribed to that named topic. Using
this model, you could safely auto-acknowledge messages using onMessage()
since every client has it's own copy of the message. This also has the
benefit of not relying on the queue being a ring queue to keep the number of
messages in check.

There's a good overview of how direct and topic exchanges work here:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/1.3/html/Messaging_User_Guide/chap-Messaging_User_Guide-Exchanges.html

You mentioned that you can't change how the message producer is sending
messages. You might confirm that the exchange type isn't configurable from a
settings or properties file, perhaps as a connection/queue URL.

If you really are stuck with trying to read from a direct exchange, I don't
think onMessage will work for you, at least not in the normal pattern of
usage. Only a single subscriber will ever receive the onMessage() for a
direct exchange message. Even if you use onMessage() to be notified of a new
message, never acknowledge the message, and then use the queue browser to
read all the messages in the queue, you still have a number of problems...
Under normal conditions, the broker expects someone (eventually) to
acknowledge the message. There's no guarantee that the broker will attempt
to redeliver the message to each client in succession, meaning that some
clients might miss the message. The second problem is that if you use the
queue browser to read messages you might have missed, your clients then need
to keep track of which messages are new to them and which they've already
seen before.

I may have misunderstood your situation, but if not, I would strongly
recommend you use the topic exchange -- it's really the correct tool for the
job.

Good luck,

 - Chris

On Wed, Mar 9, 2011 at 2:47 PM, Kim Garcia <jsmam97@hotmail.com> wrote:

>
> Hi Rajith,
>
> It doesn't matter if the apps are consumers or queue browsers as long as
> they share the messages (or get their own copy).
>
> I'm looking into using the javax.jms Topic object as suggested, but do the
> messages have to be sent to a topic instead of a queue? If so, then that
> won't work for me. I have messages being sent to an AMQ queue, and at this
> time, that cannot change.
>
> Thanks,
> Kim
>
>
> ----------------------------------------------------------------------------------------------------------------
>
> The answer below is assuming that all your apps are consumers and not queue
> browsers.
> If thats not the case then please let me know.
>
> Rajith
>
> On Wed, Mar 9, 2011 at 9:53 AM, Rajith Attapattu <rajith77@gmail.com>
> wrote:
>
> > Kim,
> >
> > If you want all the apps (consumers) on the same queue to get all the
> > messages in the queue, then using 'Queues (as in JMS terms)' is not going
> > to do it.
> > As in a shared queue situation the messages will be distributed among
> them.
> >
> > Therefore you should use a Topic and all your consumers will get a copy
> of
> > every message sent to that topic.
> >
> > Regards,
> >
> > Rajith
> >
> >
> > On Wed, Mar 9, 2011 at 12:05 AM, Kim Garcia <jsmam97@hotmail.com> wrote:
> >
> >>
> >> Rajith,
> >>
> >> I have been trying to respond to your email all day but Hotmail keeps
> >> saying the delivery has failed...
> >>
> >>
> >>
> ----------------------------------------------------------------------------------------------------------------------------
> >>
> >> Thank you for looking into this, Rajith.
> >>
> >> I'm not using any
> >> tools to verify if the message has been acked. I am running 2 of the
> >> same Java application. If I only run one, then it will get the messages
> >> like normal. If I run 2, they do not both get the same messages. I see
> >> that if app #1 gets message #1, then app #2 will not get message #1. The
> >> same applies for messages app #2 gets -- app #1 will not get them. I
> >> would like several apps to monitor the same queue with a listener and
> >> for all apps to get all of the messages.
> >>
> >> Thanks.
> >>
> >> > Date: Mon, 7 Mar 2011 18:07:19 -0500
> >> > Subject: Re: onMessage() always acknowledges msg even if Session is
> set
> >> to CLIENT_ACK
>
>

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