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https://issues.apache.org/jira/browse/AMQ-6667?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15994642#comment-15994642
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Gary Tully commented on AMQ-6667:
---------------------------------

increasing the audit capacity; policyEntry maxProducersToAudit=200 ensures the 
cursor audit tracks up to 200 producers and traps the duplicate from the store. 
In addition, disabling concurrentStoreAndDispatch avoids the issue.

The root cause is enabling the cursor cache when there are pending sends 
leaving a possible scenario where a sync send is lost behind sufficient async 
sends that fill the cache. Reverting to the store in this case results in 
duplicates.

> Many instances of "duplicate message ... from cursor" redirecting to dlq
> ------------------------------------------------------------------------
>
>                 Key: AMQ-6667
>                 URL: https://issues.apache.org/jira/browse/AMQ-6667
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: KahaDB
>    Affects Versions: 5.14.0
>            Reporter: Gary Tully
>            Assignee: Gary Tully
>             Fix For: 5.15.0
>
>
> In a high throughput scenario on a single destination there can be many 
> warnings of this kind:
> {code}
> [2017-03-21 09:51:37,548] WARN ActiveMQ BrokerService[localhost] Task-5 Queue 
> - queue://TEST, subscriptions=10, memory=102%, size=399, 
> pending=0, duplicate message ActiveMQTextMessage {commandId = 72, 
> responseRequired = true, 
> messageId = ID:Mac.fritz.box-64479-1490086286066-183:1:1:1:68, 
> originalDestination = null, originalTransactionId = null, 
> producerId = ID:Mac.fritz.box-64479-1490086286066-183:1:1:1, destination = 
> queue://TEST, transactionId = null, expiration = 0, 
> timestamp = 1490086297427, arrival = 0, brokerInTime = 1490086297427, 
> brokerOutTime = 1490086297427, correlationId = null, replyTo = null, 
> persistent = true, 
> type = null, priority = 4, groupID = null, groupSequence = 0, 
> targetConsumerId = null, compressed = false, userID = null, 
> content = org.apache.activemq.util.ByteSequence@8672edc, marshalledProperties 
> = null, dataStructure = null, redeliveryCounter = 0, size = 50216, properties 
> = null, 
> readOnlyProperties = false, readOnlyBody = false, droppable = false, 
> jmsXGroupFirstForConsumer = false, text = ...XXXXXXXXXXXX} 
> from cursor, is cursor audit disabled or too constrained? Redirecting to dlq
> {code}
> The broker loads messages twice into the cursor.



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