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From "Tim Bain (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (AMQ-2711) conduitSubscriptions flag on networkConnector element should only affect queues, not topics
Date Wed, 03 Dec 2014 16:30:14 GMT

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

Tim Bain edited comment on AMQ-2711 at 12/3/14 4:29 PM:
--------------------------------------------------------

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.


was (Author: tbain98):
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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