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From "Gary Tully (JIRA)" <j...@apache.org>
Subject [jira] Created: (AMQ-2198) Allow suppression of duplicate queue subscriptions in a cyclic network topology
Date Tue, 07 Apr 2009 19:33:34 GMT
Allow suppression of duplicate queue subscriptions in a cyclic network topology
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                 Key: AMQ-2198
                 URL: https://issues.apache.org/activemq/browse/AMQ-2198
             Project: ActiveMQ
          Issue Type: Improvement
          Components: Broker
    Affects Versions: 5.2.0
            Reporter: Gary Tully
            Assignee: Gary Tully
             Fix For: 5.3.0


in a cyclic network of brokers (where each broker knows about each other) it is possible to
have a cyclic graph and multiple routes across the network. this occurs because some brokers
pick up the second order advisories that arise from a broker responding to an advisory from
another broker. The result is that a consumer on one broker can manifest itself as multiple
consumers on brokers across the network. Network priority gives precedence to the shortest
route when it is configured. This enhancement would ensure that there is only one route for
a given destination and makes the network more deterministic and a little simpler. With small
numbers of brokers in the network, this is often what you want.

When topics are involved, the duplication leads to duplicate messages so duplicates for topics
are suppressed by default on trunk and will be in 5.3. For queues, as the message goes to
just one consumer, there is no duplicate issue, just some indeterminism in how a message is
routed through the network. This indeterminism is a means of fault tolerance and can be a
good thing so this feature is enabled via configuration for queues.

see some more background on the topic case @ https://issues.apache.org/activemq/browse/AMQ-2030

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