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From "Ivo Danihelka (JIRA)" <>
Subject [jira] Reopened: (AMQ-855) Add support for prefetchSize = 0
Date Sat, 14 Oct 2006 22:47:17 GMT
     [ ]

Ivo Danihelka reopened AMQ-855:

There remains a bug to be fixed. The method MessageConsumer.receive() does not block at all
when prefetchSize=0 is used.

The current code for ActiveMQMessageConsumer.receive() behaves like ActiveMQMessageConsumer.receiveNoWait().
The receive() could be fixed by using sendPullCommand(0) instead of sendPullCommand(-1). The
sendPullCommand(0) works for me.

Thanks. My usage of activemq includes distributed slow consumers, so I'm very happy to be
able to use zero prefetch.

Out of topic note:
It seems to me that it would be safer to use AtomicBoolean for field PrefetchSubscription.dispatching.

> Add support for prefetchSize = 0
> --------------------------------
>                 Key: AMQ-855
>                 URL:
>             Project: ActiveMQ
>          Issue Type: New Feature
>          Components: Broker
>    Affects Versions: 4.0.2, 4.0.1, 4.0
>         Environment: any
>            Reporter: Vadim Pesochinskiy
>         Assigned To: Hiram Chirino
>            Priority: Critical
>             Fix For: 4.1
>         Attachments:, ActiveMQMessageConsumer.patch,
> This feature would enable to support following test case:
> 2 servers are processing 3 submitted jobs with following processing times 10 min, 1 min,
1 min. This sequence should finish in 10 minutes as one service will pick up the 10 minutes
job, meanwhile the other one should manage the two 1 minute jobs. Since I cannot set prefetchSize=0,
one of the 1 minute jobs is sitting in prefetch buffer and the jobs are processed in 11 minutes
instead of 10.
> This is simplification of the real scenario where I have about 30 consumers submitting
jobs to 20 consumers through AMQ 4.0.1. I have following problems:
> • Messages are sitting in prefetch buffer are not available to processors, which results
in a lot of idle time.
> • Order of processing is random. For some reason Job # 20 is processed after Job # 1500.
Since senders are synchronously blocked this can result in time-outs.
> • Some requests are real-time, i.e. there is a user waiting, so the system cannot wait,
so AMQ-850 does not fix this issue.

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