[jira] [Commented] (AMQ-2711) conduitSubscriptions flag on networkConnector element should only affect queues, not topics

["Tim Bain (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AMQ-2711?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14233163#comment-14233163 ] 

Tim Bain commented on AMQ-2711:
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If you force `conduitSubscriptions=true` for topics, you lose the ability to ensure that only messages that actually have a consumer on broker A will be forwarded from broker B, which could be important if there's a bandwidth-limited link between the two.

With `conduitSubscriptions=true`, selectors are ignored and *all* messages are passed from B to A, even if all consumers on A have selectors that will exclude the message.  In certain scenarios the duplicate messages that could result from setting `conduitSubscriptions=false` would be better than the use of limited bandwidth to pass messages that will be immediately discarded on broker A.  And it's not "almost inevitable" that `conduitSubscriptions=false` will case problems; you won't get duplicate messages if all consumers have unique selectors such that a message is only ever delivered to a singe consumer.

Allowing both values of `conduitSubscriptions` for both destination types doesn't hurt anything and it gives configuration options that are useful in certain situations, so let's close this as Won't Fix.

> conduitSubscriptions flag on networkConnector element should only affect queues, not topics
> -------------------------------------------------------------------------------------------
>
>                 Key: AMQ-2711
>                 URL: https://issues.apache.org/jira/browse/AMQ-2711
>             Project: ActiveMQ
>          Issue Type: Improvement
>          Components: Connector
>    Affects Versions: 5.3.1
>            Reporter: Fintan Bolton
>             Fix For: 5.x
>
>
> In the doc for 'Networks of Brokers', http://activemq.apache.org/networks-of-brokers.html, it says that it is sometimes useful to disable {{conduitSubscriptions}} for queues, because this gives you a better load balancing effect when consumers are attached to various points in the broker network. The only trouble is, currently it does not seem practical to disable {{conduitSubscriptions}}, because this almost inevitably causes trouble with topics. That is, it can easily happen that topic messages are duplicated, if {{conduitSubscriptions}} is set to {{false}}.
> It seems like it would be better if topic subscriptions where *always* treated as conduits and the {{conduitSubscriptions}} attribute only affected queue subscriptions. That way, you could happily disable conduits for queues while leaving it enabled for topics.
> A bit of investigation is probably needed, however, to make sure that there aren't any edge cases where you might actually want to disable conduit subscriptions for topics.



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