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From "Gary Tully (JIRA)" <j...@apache.org>
Subject [jira] Commented: (AMQ-2102) Master/slave out of sync with multiple consumers
Date Thu, 05 Mar 2009 19:15:44 GMT

    [ https://issues.apache.org/activemq/browse/AMQ-2102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=50234#action_50234
] 

Gary Tully commented on AMQ-2102:
---------------------------------

sorry, my patch is still a bit of a work in progress. I was using this jira as a shared holder.
For the cce,{code} private QueueMessageReference getMatchingMessage(MessageDispatchNotification
messageDispatchNotification) throws Exception {code} needs to return a QueueMessageReference.

Add the following to get it to work better. I still need to validate that the dispatch that
that happens here is correct w.r.t a normal dispatch. I have run it by applying the patch
to trunk, so only with your changes to MasterBroker, ignoring the MasterBroker changes in
the patch. With 30000 messages I still get errors, but of a different kind. More work needed.

{code}
            if (message == null) {            
                synchronized (messages) {
                    try {
                        messages.reset();
                        while (messages.hasNext()) {
                            MessageReference node = messages.next();
+                            node.incrementReferenceCount();
+                            messages.remove();
                            if (messageId.equals(node.getMessageId())) {
+                                message = this.createMessageReference(node.getMessage());
{code}

> Master/slave out of sync with multiple consumers
> ------------------------------------------------
>
>                 Key: AMQ-2102
>                 URL: https://issues.apache.org/activemq/browse/AMQ-2102
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.2.0
>            Reporter: Dan James
>            Assignee: Gary Tully
>         Attachments: master.xml, MasterSlaveBug.java, MasterSlavePatch.patch, slave.xml,
slaveDispatchOnNotification.patch
>
>
> I'm seeing exceptions like this in a simple master/slave setup:
> ERROR Service                        - Async error occurred: javax.jms.JMSException:
Slave broker out of sync with master: Dispatched message (ID:DUL1SJAMES-L2-1231-1233929569359-0:4:1:1:207)
was not in the pending list for MasterSlaveBug
> javax.jms.JMSException: Slave broker out of sync with master: Dispatched message (ID:DUL1SJAMES-L2-1231-1233929569359-0:4:1:1:207)
was not in the pending list for MasterSlaveBug
> The problem only happens when there are multiple consumers listening to the queue, and
is more likely to occur as there are more consumers listening.  I've written a test program
that demonstrates the problem.
> I start the master and slave with an empty data directory and let them both startup and
settle.  Then start the test program.  The test program creates a specified number of consumers,
and then starts queuing 256 messages.  The consumers process the message by sending a reply.
 The producer counts the replies.  Both consumers and the producer see all the messages, but
with multiple consumers it is very likely that the error above will occur and several of the
messages will still be queued on the slave.
> While debugging through the activemq code, I noticed that both the master and the slave
dispatch the message to a consumer's pending list independently.  In other words, it is possible
that the master will add the message to consumer A's pending list and the slave will add the
message to consumer B's pending list.  Once the message has been processed by consumer A,
the master sends a message to the slaving which specifies consumer A so that the slave can
remove the message.  The slave looks on its copy of consumer A's pending list and cannot find
the message.  As a result, it throws this exception and the message stays stuck on consumer
B's pending list on the slave.
> Master and slave configurations along with MasterSlaveBug.java are attached to this issue.
> Start master and slave brokers:
> activemq xbean:master.xml
> activemq xbean:slave.xml
> Run with (only one consumer, the bug does not appear):
>    java -classpath .:activemq-all-5.2.0.jar MasterSlaveBug 1
> Run with (sixteen consumers, the bug does appear):
>    java -classpath .:activemq-all-5.2.0.jar MasterSlaveBug 16

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