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https://issues.apache.org/jira/browse/AMQ-5249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14267560#comment-14267560
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Gary Tully commented on AMQ-5249:
---------------------------------

@Alex - there was a change of behaviour in 5.10 - to treat duplicates from the 
store a as problem - in the past, they were ignored by the cursor but could get 
redispatched on a restart or if the audit was exhausted, they would be 
redispatched as duplicates. in 5.10, if the page in logic from the store gets a 
duplicate if does the DLQ thing. So in some ways the difference between 5.9 and 
5.10 is expected.
What is unknown is what exact scenario causes the behaviour you see.
The trigger for the duplicates I tracked in the past was queue memory limit 
being reached with concurrent producers to the same destination, some of which 
were transactional. The interleaving could leave the cursor and store out of 
sync, such that when the cursor needed to page in from the store, it would use 
the wrong start point.
Your trigger seems to be related to the network bridge, which would introduce a 
non transacted client ack consumer and non transacted producer. Maybe you can 
simulate that at load without the bridge.
We need to determine the sequence of events that lead to the duplicate from the 
store to understand if it is legitimate or not and if not, to ensure we don't 
fill the DLQ in this case.

> "cursor got duplicate" error after upgrade
> ------------------------------------------
>
>                 Key: AMQ-5249
>                 URL: https://issues.apache.org/jira/browse/AMQ-5249
>             Project: ActiveMQ
>          Issue Type: Bug
>    Affects Versions: 5.9.1, 5.10.0
>            Reporter: Rural Hunter
>
> I was using 5.9.0 and meet one problem so I tried to upgrade activemq. I 
> tried both 5.9.1 and 5.10.0 and encouterred a same problem. I saw messages 
> filled DLQ very quickly. I checked the clients both producer and consumer but 
> there was no error. I checked activemq log and found the log is full of these 
> warnings:
> 2014-06-27 23:22:09,337 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.cyyun.webmon.spider.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:211.com-52399-1400732399425-1:1:235992:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> 2014-06-27 23:22:09,337 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.xxxx.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:nbzjjf22805-34129-1403880308671-1:1:28:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> 2014-06-27 23:22:09,338 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.xxxxx.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:jxncxnj2-48598-1403856107346-1:1:6007:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> 2014-06-27 23:22:09,338 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.xxxx.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:jxnc17-60227-1400730816361-1:1:149072:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> 2014-06-27 23:22:09,339 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.xxxx.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:cyyun-46954-1403800808565-1:1:9765:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> 2014-06-27 23:22:09,339 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.xxxx.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:ubuntu-55495-1403497638437-1:1:53086:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> 2014-06-27 23:22:09,340 | WARN  | 
> org.apache.activemq.broker.region.cursors.QueueStorePrefetch@19117501:com.xxxx.update,batchResetNeeded=false,storeHasMessages=true,size=211,cacheEnabled=true,maxBatchSize:200,hasSpace:true
>  - cursor got duplicate: ID:cyyun-39030-1403880008363-1:1:70:1:1, 4 | 
> org.apache.activemq.broker.region.cursors.AbstractStoreCursor | ActiveMQ 
> Broker[localhost] Scheduler
> The problem mostly happens right after activemq starts and sometimes happened 
> after activemq worked normally for a while.
> For now I have to roll back to 5.9.0 and the problem doesn't occure.



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