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From "Gary Tully (JIRA)" <>
Subject [jira] Commented: (AMQ-2567) Zero Prefetch not working
Date Thu, 28 Jan 2010 10:51:40 GMT


Gary Tully commented on AMQ-2567:

done for 5.3.1-SNAPSHOT

> Zero Prefetch not working
> -------------------------
>                 Key: AMQ-2567
>                 URL:
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.3.0
>         Environment: Unix/Windows, Java 1.6
>            Reporter: Rudolf Janz
>            Assignee: Gary Tully
>             Fix For: 5.3.1, 5.4.0
>         Attachments:,,
> I have problems using the zero prefetch. The consumer starts prefetching messages after
some receives. 
> Our use case is, that we have a large computation which is split into smaller sub jobs.
These jobs are sent via ActiveMQ to some processing nodes on different machines. The duration
of jobs differs very much (10s to some minutes). The jobs are sent by decreasing estimated
computation time. If one of the consumers which receives a large job prefetches some other
jobs, these will be processed later. In the meantime the remaining consumers are idle, and
the total computation time is much longer than necessary.
> I have modified the existing ZeroPrefetchConsumerTest to test for the problem (I have
removed the other test methods). 
> Two consumers (C1  and C2) are instantiated. These messages are sent:
> 1,2,3,4,5,6,7,8,9
> C1 reads 4 times, receives 1,2,3,4 -> this is correct
> now C2 reads, it receives 8 not 5, which is the next message in the queue. The reason
is, that C1 prefetched 5, 6, 7, that should not have happened.(sometimes C1 only prefetches
> The problem can be seen in the JMX Console as well, after a while, the first consumer
has more than one dispatched message and the queue has an InflightCount of 3, although there
are only two consumers!
> The last version that we used was 4.1.1, that worked.

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