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https://issues.apache.org/activemq/browse/AMQNET-243?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=58840#action_58840
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Mark Gellings edited comment on AMQNET-243 at 4/14/10 3:22 PM:
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Attached is sample code on how we implemented an Idempotent Consumer pattern on
top of NMS.
Basic execution logic goes like this...the IdempotentListener<TMessage>
Prehook( ) method is called before a message is processed. If it is the
original message (redelivered counter 0) then we check to see if the message is
in the database, if it is we send it through as redelivered (by throwing our
RecoverableMessageException) so the listener logic can process as a redelivery.
Notes:
--When coding this I tried to follow the Idempotent Consumer pattern in Apache
Camel as close as possible
--I understand some of this code may not make sense (e.g. extension methods,
it's a layer of abstraction above ActiveMQ.NMS, some code is missing).
Unfortunately I can't submit that code.
--While it may make sense to have a Camel.Net sub project, it may be overkill
as I don't see other EIP being implemented. If adding this logic to NMS, the
database connection needs to remain agnostic. As you can see we used
iBATIS.NET to connect to the database, so theoretically any database platform
could be used. But ultimately we wouldn't want ActiveMQ.NMS to have iBATIS
dependencies. Perhaps an IMessageDao implementation would be required and set
on initialization to enable an Idempotent Consumer. Then NMS is not
responsible for the implementation of the database access.
All else aside, attached is an example of how to code it.
was (Author: magellings):
Attached is sample code on how we implemented an Idempotent Consumer
pattern on top of NMS.
Basic execution logic goes like this...the IdempotentListener<TMessage>
Prehook( ) method is called before a message is processed. If it is the
original message (redelivered counter 0) then we check to see if the message is
in the database, if it is we send it through as redelivered (by throwing our
RecoverableMessageException) so the listener logic can process as a redelivery.
Notes:
--When coding this I tried to follow the Idempotent Consumer pattern in Apache
Camel.
--I understand some of this code may not make sense (e.g. extension methods,
it's a layer of abstraction above ActiveMQ.NMS, some code is missing).
Unfortunately I can't submit that code.
--While it may make sense to have a Camel.Net sub project, it may be overkill
as I don't see other EIP being implemented. If adding this logic to NMS, the
database connection needs to remain agnostic. As you can see we used
iBATIS.NET to connect to the database, so theoretically any database platform
could be used. But ultimately we wouldn't want ActiveMQ.NMS to have iBATIS
dependencies. Perhaps an IMessageDao implementation would be required and set
on initialization to enable an Idempotent Consumer. Then NMS is not
responsible for the implementation of the database access.
All else aside, attached is an example of how to code it.
> failover causes duplicate messages
> ----------------------------------
>
> Key: AMQNET-243
> URL: https://issues.apache.org/activemq/browse/AMQNET-243
> Project: ActiveMQ .Net
> Issue Type: Bug
> Components: NMS
> Affects Versions: 1.1.0
> Reporter: Mark Gellings
> Assignee: Jim Gomes
> Attachments: IdempotentConsumer.zip
>
>
> Reference https://issues.apache.org/activemq/browse/AMQ-2627 for specifics on
> problem.
> Attached to that issue is a zip file which is password protected with
> password "fridaytest".
> We're using ActiveMQ v5.2, jdbc master/slave MSSQL 2008. Attached is an NMS
> v1.2 RC4 consumer with a transacted session as well as activemq.xml.
> To replicate:
> 1) Work through the console prompts and produce 50 msgs.
> 2) Restart console and start consuming those 50 msgs.
> 3) In the middle of the consumer processing, restart broker
> 4) The last message consumer was processing will be resent and not marked as
> redelivered. (this is the idempotent msg problem. Ex. - instead of $500
> getting deposited into your account, $1000 does)
> 5) Then NMS blows up which seems like a different problem?
> From what I understand this shouldn't be the case if you use a transacted
> session, however the attached console app can prove it is a problem.
> Bottomline--I thought this was why the camel idempotent consumer pattern [1]
> existed which can be leveraged by java clients.
> [1] http://fusesource.com/docs/router/1.6/eip/MsgEnd-Idempotent.html
> Regards,
> Mark
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