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From "Andrew May (JIRA)" <j...@apache.org>
Subject [jira] [Created] (AMQ-4720) Messages lost after fail-back of a network connector using priorityBackup=true - reason is that remote broker isn't checking producerID & is rejecting because of duplicate producerSequence
Date Wed, 11 Sep 2013 11:26:54 GMT
Andrew May created AMQ-4720:
-------------------------------

             Summary: Messages lost after fail-back of a network connector using priorityBackup=true
- reason is that remote broker isn't checking producerID & is rejecting because of duplicate
producerSequence
                 Key: AMQ-4720
                 URL: https://issues.apache.org/jira/browse/AMQ-4720
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 5.8.0
         Environment: Only tested on Windows 7 Enterprise x64.
            Reporter: Andrew May


Summary of problem:
-------------------
If a static failover network connector is setup to connect to 2 other brokers & to fail-back
to a priority broker; messages can be lost after fail-back because the remote broker deletes
them due to duplicate producer-sequence numbers even though the producer-id has changed.
My suspicion is that the remote broker doesn't recognise that the re-established connection
is a network connection & so doesn't check producer-id.


Test-harness setup:
-------------------
Using ActiveMQ 5.8.0 binary download.
Only changes are to logging settings & to the configuration file.

3 brokers ("amq1", "amq2", "amq3"), all brokers running on localhost.
Each uses their own config file (amq1.xml, amq2.xml, amq3.xml)

Broker amq1 has a failover duplex connection to amq2.
Broker amq3 has a duplex failover connection to both amq1 + amq2, it is configured to always
try to connect to amq1 first ("randomize=false") and to fail-back to amq1 if it comes back
online ("priorityBackup=true")

Consumer connects to broker amq1
Producer connects to broker amq3

Test-harness sender application creates a new session each time it is run & sends a set
of messages.
The sending session is not transacted & is set to auto-acknowledge.
Messages are sent with persistent delivery mode.
Messages are on queue "MyQueue"


Test script:
------------
Start all 3 brokers.
Broker amq3 establishes a connection to amq1.
Broker amq1 establishes a connection to amq2.

Consumer connects to amq2 & starts consuming queue "MyQueue".
Producer connects to amq3 & sends 10 messages on queue "MyQueue" - these are all passed
on to broker amq1 which forwards them to amq2 where they are delivered to the consumer.
Producer connects to amq3 & sends 10 messages on queue "MyQueue" - these are all delivered
as before - N.B. producerID is different as this is a new connection.

Broker amq1 is shut down.
Broker amq3 fails-over to connect to amq2.

Producer connects to amq3 & sends 10 messages on queue "MyQueue" - these are all passed
directly to amq2 where they are delivered to the consumer - (as before, the producer-id has
changed).
Producer connects to amq3 & sends 10 messages on queue "MyQueue" - these are delivered
as before.

Broker amq1 is restarted 
Broker amq1 re-establishes its connection to amq2.

Broker amq3 notices that amq1 is available & fails-back to it.
    - Broker amq3 closes its connection to amq2
    - Broker amq3 starts a new connection to amq1

Producer connects to amq3 & sends 10 messages on queue "MyQueue" - these are all passed
directly to amq2 where they are delivered to the consumer - (as before, the producer-id has
changed).
    - N.B. Immediately before the first message is received & forwarded by amq1, amq1's
log shows:
        2013-09-11 12:05:56,639 | DEBUG | last stored sequence id set: -1 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
      ---> This message only appears after fail-back, it doesn't appear earlier.
           This is indicative of the network connection being treated differently after fail-back.

**********************
** Error occurs now **
**********************

** Producer connects to amq3 & sends 20 messages on queue "MyQueue" (with a different
producer-ID)
    - The first 10 are deleted by broker amq2 because it thinks that they have a duplicate
sequence ID.
    - amq1 log shows:
        2013-09-11 12:06:29,201 | DEBUG | suppressing duplicate message send [ID:bd7ewandymay-56895-1378897588954-0:1:1:1:1]
with producerSequenceId [1] less than last stored: 10 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
        2013-09-11 12:06:29,223 | DEBUG | suppressing duplicate message send [ID:bd7ewandymay-56895-1378897588954-0:1:1:1:2]
with producerSequenceId [2] less than last stored: 10 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
        ... snip ...
        2013-09-11 12:06:29,396 | DEBUG | suppressing duplicate message send [ID:bd7ewandymay-56895-1378897588954-0:1:1:1:10]
with producerSequenceId [10] less than last stored: 10 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
    - The last 10 are successfully forwarded to amq2, where they are consumed.

** Producer connects to amq3 & sends 30 messages on queue "MyQueue" (with a different
producer-ID)
    - The first 20 are deleted by broker amq2 because it thinks that they have a duplicate
sequence ID.
    - amq1 log shows:
        2013-09-11 12:06:45,668 | DEBUG | suppressing duplicate message send [ID:bd7ewandymay-56899-1378897605440-0:1:1:1:1]
with producerSequenceId [1] less than last stored: 20 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
        2013-09-11 12:06:45,682 | DEBUG | suppressing duplicate message send [ID:bd7ewandymay-56899-1378897605440-0:1:1:1:2]
with producerSequenceId [2] less than last stored: 20 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
        ... snip ...
        2013-09-11 12:06:45,959 | DEBUG | suppressing duplicate message send [ID:bd7ewandymay-56899-1378897605440-0:1:1:1:20]
with producerSequenceId [20] less than last stored: 20 | org.apache.activemq.broker.ProducerBrokerExchange
| ActiveMQ Transport: tcp:///172.16.7.85:56880@61616
    - The last 10 are successfully forwarded to amq2, where they are consumed.


It looks to me as if amq1 doesn't realise that the fail-back network connection established
by amq3 is a network connection & so isn't checking producer IDs.




Details of why I'm trying this configuration:
---------------------------------------------

Use case:
---------
1 central site.
Multiple branches, each with a single branch server and multiple user PCs.
Each branch only has 1 internet connection that is shared by branch server & PCs.
Branch server is typically unreliable hardware & may go offline without notice.
Resilience to network loss is important & so each PC & server has its own broker.
Both branch server & PCs need to be able to communicate with the centre

To reduce the number of connections into the centre, we would like a tree topology with the
branch server concentrating all branch PC messages & forwarding them to the centre.
But, PCs generate a data feed that we want to be able to access at centre, even when the branch
server is offline.

Proposed configuration:
-----------------------
Use a failover network connection on branch PCs & configure the connection to prioritise
a connection to the branch server, but open a direct connection to the centre if the branch
server is unavailable.

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