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From "Tkar Akai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMQ-3004) Build-up of unwanted messages
Date Fri, 16 Sep 2011 23:54:16 GMT

    [ https://issues.apache.org/jira/browse/AMQ-3004?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13106922#comment-13106922
] 

Tkar Akai commented on AMQ-3004:
--------------------------------

We would very much like to get this patch into the trunk!

Virtual Topics are a perfect match for our use case, we have a single selector per queue (multiple
consumers but each using the same selector on a given queue), and need to guarantee that the
(filtered) messages are delivered to each queue even when all the consumers disconnect (in
our case not intentionally, just dues to some failure or networking issue) and it's not acceptable
to miss messages that were published during a disconnect.

Any chance that this solution or a comparable one will make it to an an official release?


> Build-up of unwanted messages
> -----------------------------
>
>                 Key: AMQ-3004
>                 URL: https://issues.apache.org/jira/browse/AMQ-3004
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.4.1
>            Reporter: Roelof Naude
>         Attachments: AMQ-3004.patch
>
>
> One of our installations have several consumers. These consumers subscribe for messages
from a queue linked to a virtual topic. All consumers supply a selector. Some consumers connect,
process any persisted messages, then disconnect. These connect/disconnect cycles are repeated
a few times a day.
> What we've seen is that messages build-up for consumers. These messages does not match
the supplied selector. The side effect of this was that we ran into a situation whereby message
"got stuck". Increasing the _maxPageSize_ property helped. This is unfortunately a short term
solution.
> A simple test was constructed whereby *selectorAware* was set to *true*:
> {code:xml}
> <virtualDestinations>
>   <virtualTopic name="VirtualTopic.>" prefix="Consumer.*." selectorAware="true"/>
> </virtualDestinations>
> {code}
> What we noticed is that:
> # Messages are correctly received by a connected consumer
> # A consumer that connects, disconnects and re-connects later will loose any messages
that were send in the time period it was disconnected.
> This behaviour was unexpected. From the AMQ documention (http://activemq.apache.org/virtual-destinations.html):
> {quote}
> From version 5.4, dispatch from virtual topics to subscription queues can be selectorAware
such that only messages that match one of the existing subscribers are actually dispatched.
Using this option prevents the build up of unmatched messages when selectors are used by exclusive
consumers
> {quote}
> Note: it does not state that the consumer needs to be connected for this feature to work.
> Given the test it looks like subscriptions itself are not persisted, thus the AMQ broker
has no idea that it should enqueue a message for a particular subscription queue.
> Would it be possible to add either of:
> # Persist subscription detail, specifically for the case where the subscription's selector
should be applied to the subscription queue
> # Propagate selectors and the attached  subscription queue to the top-level virtual topic
so that only interested messages can be delivered to the intended recipient?
> Anything else we can try, supply or help with?

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