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Date: Sat, 14 Oct 2006 15:47:17 -0700 (PDT)
From: "Ivo Danihelka (JIRA)" <jira@apache.org>
To: activemq-dev@geronimo.apache.org
Subject: [jira] Reopened: (AMQ-855) Add support for prefetchSize = 0
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     [ https://issues.apache.org/activemq/browse/AMQ-855?page=3Dall ]

Ivo Danihelka reopened AMQ-855:
-------------------------------

            =20
There remains a bug to be fixed. The method MessageConsumer.receive() does =
not block at all when prefetchSize=3D0 is used.

The current code for ActiveMQMessageConsumer.receive() behaves like ActiveM=
QMessageConsumer.receiveNoWait(). The receive() could be fixed by using sen=
dPullCommand(0) instead of sendPullCommand(-1). The sendPullCommand(0) work=
s for me.

Thanks. My usage of activemq includes distributed slow consumers, so I'm ve=
ry 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 Prefet=
chSubscription.dispatching.

> Add support for prefetchSize =3D 0
> --------------------------------
>
>                 Key: AMQ-855
>                 URL: https://issues.apache.org/activemq/browse/AMQ-855
>             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.java.patch3, ActiveMQMessage=
Consumer.patch, ActiveMQMessageConsumer.patch2, PrefetchSubscription.java.p=
atch2, PrefetchSubscription.java.patch3, PrefetchSubscription.patch, region=
.QueueSubscription.java.patch, ZeroPrefetchConsumerTest.java.patch, ZeroPre=
fetchConsumerTest.java.patch3
>
>
> 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 ser=
vice will pick up the 10 minutes job, meanwhile the other one should manage=
 the two 1 minute jobs. Since I cannot set prefetchSize=3D0, one of the 1 m=
inute jobs is sitting in prefetch buffer and the jobs are processed in 11 m=
inutes instead of 10.
> This is simplification of the real scenario where I have about 30 consume=
rs submitting jobs to 20 consumers through AMQ 4.0.1. I have following prob=
lems:
> =95 Messages are sitting in prefetch buffer are not available to processo=
rs, which results in a lot of idle time.
> =95 Order of processing is random. For some reason Job # 20 is processed =
after Job # 1500. Since senders are synchronously blocked this can result i=
n time-outs.
> =95 Some requests are real-time, i.e. there is a user waiting, so the sys=
tem cannot wait, so AMQ-850 does not fix this issue.

--=20
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