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From jvh <jhuffna...@comcast.net>
Subject Use of MirroredQueues results in OutOfMemoryError
Date Tue, 24 Mar 2009 20:20:11 GMT

We are experiencing an OutOfMemoryError when using MirroredQueues and I was
wondering if someone could comment on whether our use (or interpretation) of
these Mirrored Queues is correct, or if there is a bug in the BrokerService
code.

In our case, we have an existing application “A” that uses messaging, but we
now have a new application “B” that will only sometimes monitor the
messaging on the original application “A”.  We don’t want the first
application “A” to have to know about, or to do anything different if
application “B” is there listening to the messages or not.

This seemed like a decent use of MirroredQueues (since they evidently create
a “topic” that can be used as a wire-tap), but evidently by setting
BrokerService.setUseMirroredQueues(true) on the broker for Project “A”,
we’ve introduced a rather large memory leak.

The objects that appear to grow in number are:
org.apache.activemq.store.memory.MemoryTransactionStore$2
org.apache.activemq.store.memory.MemoryTopicMessageStore
org.apache.activemq.command.ActiveMQTopic

This seems to suggest the mirrored messages are being retained, but the
Broker has setPersistent(false) specified and I don’t see any way to set
Time to Live, or any other way for the Broker to monitor and remove if
necessary on the Mirrored Queue only, etc..  If I look at the queues via
jConsole MBeans, I can see the Topic.VirtualTopic.Mirror.DacIncomingQueue
with attributes showing that the messages are only being enqueue and not
dequeued.  I really want the Broker to drop these messages if Application
“B” is not there to dequeue them.  

Is it recommended that we use MirroredQueues to do this?  If so, what’s the
best way to set things up so I don’t have a memory problem if the other
application is not listening to the mirroredQueue? … and if not, we would
appreciate any other suggestions.

---- For attached Example Code----
The code attached is a simplified version of our Project “A” only and
represents the case where Project “B” is not online (and not included in
this example at all in fact) … it does show our use of Spring Templates to
set up the Broker (and the producer and consumer clients).  I’ve tried to
remove quite a bit of the extraneous stuff to try to get it down to the
basic problem, but I apologize that it still has a bit of fluff.  I’ve also
arranged things such that the broker is in a separate JVM to more easily see
the memory growth of this component.  The BrokerService is specified in the
jms.broker.BrokerBean class.

For the attached code and the 8MB specified for the JVM, we get about 3542
messages before the broker dies with an OutOfMemoryError

I’ve also noticed that there is a BrokerService.setUseTempMirroredQueue()
method and wonder if that is more appropriate for my use since it implies
that the Mirrored Queue will be temporary, but the JavaDoc for this message
is empty and I’ve seen nothing on the forums as to its characteristics and
proper use.  When I do use the Temporary Mirrored Queues, I also don’t see
the same Virtual Topic that should be created that I see with the regular
MirroredQueue topic (i.e. I don’t see VirtualTopic.Mirror.Foo.Bar being
created for a queue of Foo.Bar), so this doesn’t seem to fit our needs.

If you want to run the code, run jms-broker first, then run jms-client
(client contains both a message producer and consumer).  There is a
README.txt file in the top level directory of each application for build and
execution instructions.

Using ActiveMQ 5.2.0 and Spring 2.5.4 on a Windows XP SP2 platform (but
we’ve seen this on unix platforms as well) and I’ve been using jconsole, and
jvisualvm to monitor memory growth and queues

http://www.nabble.com/file/p22688889/jmsMirroredQueueExample.zip
jmsMirroredQueueExample.zip 
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