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From "Yuriy Sidelnikov (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (AMQ-4107) Message order can be broken for Topic under a high load when topicPrefetch=1 and comsumer is slow
Date Mon, 15 Oct 2012 08:14:02 GMT

     [ https://issues.apache.org/jira/browse/AMQ-4107?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Yuriy Sidelnikov updated AMQ-4107:
----------------------------------

    Description: 
For <amq:policyEntry topic=">" producerFlowControl="true" memoryLimit="30mb" topicPrefetch="1"
blockedProducerWarningInterval="30">

Short excerpt from TopicSubscription class:
public void add(MessageReference node) throws Exception {

…..
              if ({color:red}!isFull(){color} && matched.isEmpty()  && !isSlave())
{
            // if maximumPendingMessages is set we will only discard messages which
            // have not been dispatched (i.e. we allow the prefetch buffer to be filled)
            dispatch(node);                   <- Second message will go this way and might
be dispatched sooner than first one.
            setSlowConsumer(false);
        } else {
…….
if (matched.tryAddMessageLast(node, 10)) {    <- first message will be put in the VMCursor
queue and might be dispatched later 
                            break;
                        }
.....
 dispatchMatched();   <- First message won't be dispatched immediately because !isFull()
is still false
}
Possible scenario as I can see it from logs:
1. First message has arrived and !isFull() is false because consumer didn't take some previous
message yet.
2. First message will be processed by tryAddMessageLast in VMPendingMessageCursor class and
will be dispatched very lately because !isFull() is still false.
3. Meanwhile consumer reads some previous message and !isFull() will return true.    
4. Second message will be dispatched immediately and might be first to be delivered. 
5. Then first message is dispatched.
6. Message order is broken.


  was:
For <amq:policyEntry topic=">" producerFlowControl="true" memoryLimit="30mb" topicPrefetch="1"
blockedProducerWarningInterval="30">

Short excerpt from TopicSubscription class:
public void add(MessageReference node) throws Exception {

…..
              if (!isFull() && matched.isEmpty()  && !isSlave()) {
            // if maximumPendingMessages is set we will only discard messages which
            // have not been dispatched (i.e. we allow the prefetch buffer to be filled)
            dispatch(node);                   <- Second message will go this way and might
be dispatched sooner than first one.
            setSlowConsumer(false);
        } else {
…….
if (matched.tryAddMessageLast(node, 10)) {    <- first message will be put in the VMCursor
queue and might be dispatched later 
                            break;
                        }
.....
 dispatchMatched();   <- First message won't be dispatched immediately because !isFull()
is still false
}
Possible scenario as I can see it from logs:
1. First message has arrived and !isFull() is false because consumer didn't take some previous
message yet.
2. First message will be processed by tryAddMessageLast in VMPendingMessageCursor class and
will be dispatched very lately because !isFull() is still false.
3. Meanwhile consumer reads some previous message and !isFull() will return true.    
4. Second message will be dispatched immediately and might be first to be delivered. 
5. Then first message is dispatched.
6. Message order is broken.


    
> Message order can be broken for Topic under a high load when topicPrefetch=1 and comsumer
is slow
> -------------------------------------------------------------------------------------------------
>
>                 Key: AMQ-4107
>                 URL: https://issues.apache.org/jira/browse/AMQ-4107
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Transport
>    Affects Versions: 5.6.0
>            Reporter: Yuriy Sidelnikov
>
> For <amq:policyEntry topic=">" producerFlowControl="true" memoryLimit="30mb" topicPrefetch="1"
blockedProducerWarningInterval="30">
> Short excerpt from TopicSubscription class:
> public void add(MessageReference node) throws Exception {
> …..
>               if ({color:red}!isFull(){color} && matched.isEmpty()  &&
!isSlave()) {
>             // if maximumPendingMessages is set we will only discard messages which
>             // have not been dispatched (i.e. we allow the prefetch buffer to be filled)
>             dispatch(node);                   <- Second message will go this way and
might be dispatched sooner than first one.
>             setSlowConsumer(false);
>         } else {
> …….
> if (matched.tryAddMessageLast(node, 10)) {    <- first message will be put in the
VMCursor queue and might be dispatched later 
>                             break;
>                         }
> .....
>  dispatchMatched();   <- First message won't be dispatched immediately because !isFull()
is still false
> }
> Possible scenario as I can see it from logs:
> 1. First message has arrived and !isFull() is false because consumer didn't take some
previous message yet.
> 2. First message will be processed by tryAddMessageLast in VMPendingMessageCursor class
and will be dispatched very lately because !isFull() is still false.
> 3. Meanwhile consumer reads some previous message and !isFull() will return true.   

> 4. Second message will be dispatched immediately and might be first to be delivered.

> 5. Then first message is dispatched.
> 6. Message order is broken.

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