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https://issues.apache.org/jira/browse/AMQ-3313?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Timothy Bish closed AMQ-3313.
-----------------------------

    Resolution: Not A Problem

This is working as designed, if you want to prevent the broker from eagerly 
dispatching the messages then you need to disable prefetchExtension on the 
destination policy.

usePrefetchExtension="false"

> When prefetch size=1 and ack-mode=CLIENT_ACKNOWLEDGE, 2 messages are 
> dispatched to client actually.
> ---------------------------------------------------------------------------------------------------
>
>                 Key: AMQ-3313
>                 URL: https://issues.apache.org/jira/browse/AMQ-3313
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.4.2
>         Environment: RHEL5/ MAC OS X 10.6.7
>            Reporter: Fengming Lou
>            Priority: Minor
>
> Setups:
> 1. use producer/consumer code come with the packaged examples.
> 2. Send 10 messages to test queue
> 3. Start up consumer. The consumer is modified to consume 1 messages every 30 
> seconds.
> 4. The ackMode is set to CLIENT_ACKNOWLEDGE
> 5. prefetch size=1 and 4 are tested
> 6. Monitor and reset queue data through jconsole
> Conclusion:
> 1. For prefetch size=1, broker actually dispatches 2 (1 more than prefetch).
> 2. For prefetch size=4, broker dispatch exactly 4 messages.
> Deatails:
> Test prefetch=1
> 1. Reset queue statistics, my.test (through jconsole)
> 2. Sent 10 messages to my.test(through jconsole)
> 3. Start up consumer:
> ant consumer -Durl=tcp://localhost:61616?jms.prefetchPolicy.queuePrefetch=1 
> -Dmax=10 -Ddurable=false -DtimeToLive=600000 -Dack-mode=CLIENT_ACKNOWLEDGE 
> -Dsubject=my.test
> 4. monitor consumer logs and jconsole stats.
>   The InFlight number was always equal to 2 before 9 messages were consumed.
> consumer:
>      [echo] Running consumer against server at $url = 
> tcp://localhost:61616?jms.prefetchPolicy.queuePrefetch=1 for subject $subject 
> = my.test
>      [java] Connecting to URL: 
> tcp://localhost:61616?jms.prefetchPolicy.queuePrefetch=1
>      [java] Consuming queue: my.test
>      [java] Using a non-durable subscription
>      [java] Running 1 parallel threads
>      [java] [Thread-3] We are about to wait until we consume: 10 message(s) 
> then we will shutdown
>      [java] [1302639994466 Thread-3] Received: 'Test 1' (length 6)
>      [java] [1302640024469 Thread-3] Received: 'Test 2' (length 6)
>      [java] [1302640054470 Thread-3] Received: 'Test 3' (length 6)
>      [java] [1302640084470 Thread-3] Received: 'Test 4' (length 6)
>      [java] [1302640114469 Thread-3] Received: 'Test 5' (length 6)
>      [java] [1302640144469 Thread-3] Received: 'Test 6' (length 6)
>      [java] [1302640174469 Thread-3] Received: 'Test 7' (length 6)
>      [java] [1302640204470 Thread-3] Received: 'Test 8' (length 6)
>      [java] [1302640234470 Thread-3] Received: 'Test 9' (length 6)
>      [java] [1302640264470 Thread-3] Received: 'Test 10' (length 7)
> Above test was repeated for prefetch=4. The Inflight indicates exactly 4 
> messages were dispatched.
> consumer:
>      [echo] Running consumer against server at $url = 
> tcp://localhost:61616?jms.prefetchPolicy.queuePrefetch=4 for subject $subject 
> = my.test
>      [java] Connecting to URL: 
> tcp://localhost:61616?jms.prefetchPolicy.queuePrefetch=4
>      [java] Consuming queue: my.test
>      [java] Using a non-durable subscription
>      [java] Running 1 parallel threads
>      [java] [Thread-3] We are about to wait until we consume: 10 message(s) 
> then we will shutdown
>      [java] [1302640654692 Thread-3] Received: 'Test 1' (length 6)
>      [java] [1302640684694 Thread-3] Received: 'Test 2' (length 6)
>   

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