[jira] [Commented] (AMQ-4157) KahaDBTransactionStore.removeAyncMessage may cancel addMessage when in transaction leading to unpersisted messages

["Martin Serrano (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AMQ-4157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13489683#comment-13489683 ] 

Martin Serrano commented on AMQ-4157:
-------------------------------------

Note in my integration test which does reproduce this, it failed 5 times out of 231 runs.
                
> KahaDBTransactionStore.removeAyncMessage may cancel addMessage when in transaction leading to unpersisted messages
> ------------------------------------------------------------------------------------------------------------------
>
>                 Key: AMQ-4157
>                 URL: https://issues.apache.org/jira/browse/AMQ-4157
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Message Store
>    Affects Versions: 5.7.0
>         Environment: linux 64-bit, kahadb, persisted messages, cached dest, transacted
>            Reporter: Martin Serrano
>            Priority: Blocker
>
> This was very difficult to track down.  It rarely occurs because a certain set of events must be occurring to trigger the bug.   I have marked it a Blocker because when it does occur, it is silent and leads to a message not being persisted in the MessageStore.
> *Description*
> The crux of the bug is that when a rollback on a session occurs, the resulting MessageAck can overlap with the async store of the message in the KahaDB.   When this occurs, the message is never persisted.  Additionally, the resultant {{CancellationException}} is ignored in o.a.a.broker.region.Queue:796.   The steps:
> # a StoreQueueTask is created to add a message X.  this is put on the async task queue
> # meanwhile this message is dispatched via a prefetch subscription to a transacted consumer.
> # the transacted consumer calls session.rollback
> # this leads to acknowledgement of the dispatched message
> # as a result {{destination.removeAsyncMessage()}} is called
> # if the original add has not yet executed then it will be cancelled leading to the message never being persisted!  (occurs at KahaDBStore:401)
> # the Queue.send method uses the result future to make sure the persist happens in the store, but it ignores cancellation, so this can lead execution control to return to the sender when no persistence has occurred without an error.
> I have not been able to reproduce this in a small activemq-only test.  But I can reproduce it in my environment.  
> *Proposed Solutions*
> I'm really unsure of the solution here.  Should {{KahaDBStore.removeAsyncMessage}} (line 393) check the context and only cancel tasks if it is not in a transaction context?  But what would that mean in the log?  Would there be a removeMessage prior to the addMessage?
> *Workaround*
> * turn off caching for the destination (see [dest policies|http://activemq.apache.org/per-destination-policies.html]).  this will cause messages to be added synchronously so they will not be subject to the async cancellation

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