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From "Andrew Lusk (JIRA)" <j...@apache.org>
Subject [jira] Commented: (AMQ-855) Add support for prefetchSize = 0
Date Tue, 08 Aug 2006 22:14:23 GMT
    [ https://issues.apache.org/activemq/browse/AMQ-855?page=comments#action_36713 ] 
            
Andrew Lusk commented on AMQ-855:
---------------------------------

Hiram, I don't really understand your comments here.  There is a huge need for this.  A push
model just isn't appropriate for queues.  Now, you could in theory hack together a "pull"
model by setting prefetch size = 0, so that basically each ack is a request for the next message.
 This method is slower, but it does scale out as you add more consumers.  This is a big problem
for our internal customers.

Systems like this need to be designed under the assumption that clients will not behave themselves.
 They will deadlock themselves, slow down arbitrarily, boxes will go up and down, etc.  These
things happen all the time in real life and shouldn't have adverse effects on other, well-behaved
consumers.


> Add support for prefetchSize = 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, 4.0.1, 4.0.2
>         Environment: any
>            Reporter: Vadim Pesochinskiy
>            Priority: Critical
>             Fix For: 4.2
>
>
> 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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