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