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From Eric Van Dewoestine <ervan...@gmail.com>
Subject Re: Issue creating a distributed queue using store and forward.
Date Wed, 07 Oct 2009 19:06:08 GMT
Hmm, that seems like a flawed approach if the broker it visited has
changed state and is now eligible to process those messages.  How is
this type of fail over intended to be handled with activemq?  Is there
an alternate solution that I'm missing?

On Wed, Oct 07, 2009 at 11:43:49AM -0700, Joe Fernandez wrote:
>
> I think that by design a message will not be forwarded to a broker that it
> has already visited.
>
> Joe
> http://www.ttmsolutions.com
>
>
> Eric Van wrote:
> >
> > ActiveMQ 5.3.0_SNAPSHOT (Sep 8th according to the snapshots listing)
> >
> > I'm running into an issue with the store and forward feature of
> > activemq, which I using in an attempt to create a highly available
> > distributed queue.  I'm trying to figure out if the issue is a
> > misconfiguration on my part, expected behavior of activemq, or a bug.
> >
> > The summary of the problem is that given 2 brokers, B1 and B2, which
> > each have one consumer, C1 and C2, which are subscribed to the same
> > queue.  If I stop a consumer on one of the brokers, the pending
> > messages from that broker are not always forwarded to the other broker
> > which still has a consumer, leading to those messages getting
> > indefinitely stuck.
> >
> > The steps I use to reproduce this scenario are as follows (Note: all
> > producing and consuming is performed over the stomp transport):
> >
> > Couple notes about the consumers:
> > - they have a prefetchSize of 40
> > - the processing of messages can take some time, so for the purposes
> >   of this exercise, I've created a simple consumer that sleeps for 10
> >   seconds before sending the message ack (using client-individual ack
> >   mode)
> >
> > 1. start both brokers (B1 and B2). The consumers (C1 and C2) are not
> >    yet running.
> > 2. produce a few thousand messages to B1
> >    Note: B1 now has a few thousand pending messages and B2 has 0.
> > 3. start consumer C2 (listing for messages from B2)
> >    Note: messages are are successfully received and begin processing
> >    (monitoring the brokers shows pending messages decreasing). Now B2
> >    has all the pending messages and B1 has 0.
> > 4. start consumer C1 (listing for messages from B1)
> >    Note: no messages are received, which is another issue I have since
> >    B2 now has thousands of pending messages which C1 could help
> >    process, but instead sits idle while C2 is forced to handle all the
> >    messages.
> > 5. stop consumer C2
> >    Note: now I have thousands of messages sitting on B2 and 0 on B1
> >    where a C1 is alive and ready to handle them.  So at this point,
> >    despite having a consumer running, thousands of messages are stuck
> >    in the queue.
> > 6. stop consumer C1
> >    Note: now I have no consumers.  Stopping and restarting C1 has no
> >    effect on the pending messages sitting on B1's queue.
> > 7. stop both brokers
> > 8. start B1, then start B2
> > 9. start C1
> >    Note: now all messages have migrated from B2 to B1 and C1 is again
> >    processing messages.
> >
> > So after step 5, the only way to recover from the stuck messages is to
> > restart the brokers.
> >
> > Below is my current connector config which I have on both brokers.
> > I've tried playing with the various properties of the connector, but
> > it seems as though no matter what I try the above scenario continues
> > to occur.
> >
> > <networkConnector
> >     name="default-nc"
> >     uri="multicast://default?group=${broker.group}"
> >     dynamicOnly="true"
> >     networkTTL="25"
> >     suppressDuplicateQueueSubscriptions="true"/>
> >
> >
> > So, is this an activemq bug? Am I mis-using activemq? Is there some
> > other way to achieve a highly available distributed queue?
> >
> > Any help in this regard is greatly appreciated.
> >
> > --
> > eric
> >
> >

--
eric

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