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From "ying (JIRA)" <j...@apache.org>
Subject [jira] Updated: (AMQ-2102) Master/slave out of sync with multiple consumers
Date Tue, 10 Mar 2009 15:18:39 GMT

     [ https://issues.apache.org/activemq/browse/AMQ-2102?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

ying updated AMQ-2102:
----------------------

    Attachment: AMQ-2102-03102009.patch

Attached AMQ-2102-03102009.patch seems fix all the slave broker out of synch issue. This is
patch is created on activemq 5.2.0 official release tagged source. sorry that I run a tight
schedule and don't have time to patch on trunk. 

One thing missed in this patch is:
{{{
 public MessageReference getMessage(MessageId id) throws IOException{
    	Message msg = this.store.getMessage(id);
    	return msg;
    }
}}}

in org.apache.activemq.broker.region.cursors.QueueStorePrefetch.java

Here is some explaination:

1. MasterBroker.java changes make sure that each command will arrive on the slave side in
the same order. This is necessary because for each specific message, message itself, dispatch
notification and message ack has to come in the exact order, otherwise, slave out of sync

2. Queue.java if dispatch notification comes and the messages still not in pending list or
pagedIn, it goes to the store to grab the message and add to the pending then do processMessageDispatchNotification.
This is necessary because that multiple consumers are involved (eg. dispatch notification
for message 201 could come first while only 200 messages on slave side is pagedin or in the
pending list)

Please review it. I urgently need a review of this to make sure the changes are fine.

A remaining issue which might or might related to this fix:

I see "consumer stop consuming message" when large number of messages is produced and consumed
and I have to restart the broker pair. otherwise, the brokers seems hanging. do you have any
insight what might go wrong?



> 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: AMQ-2102-03102009.patch, 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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