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From "Gary Tully (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (AMQ-2102) Master/slave out of sync with multiple consumers
Date Fri, 13 Mar 2009 12:05:40 GMT

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

Gary Tully resolved AMQ-2102.
-----------------------------

       Resolution: Fixed
    Fix Version/s: 5.3.0

fix committed, Ying, thanks for your input. r753214

slave dispatch now occurs on processDispatchNotification when master has chosen the subscriber.
With large volumes and prefetch sizes and short lived consumers messages on the slave may
not be in memory and need to be pulled directly from the store. Normally this is not the case
though.

Having the master and slave do separate dispatch does not work due to re deliveries and consumer
add/remove order and load effects on thread scheduling. with the stricter enforcement of ack
delivery to subscriptions this behavior unfolded.

> 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
>             Fix For: 5.3.0
>
>         Attachments: AMQ-2102-03102009.patch, AMQ2102.12-03.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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