Multiple consumers attached to a JMS queue automatically obey competing consumer semantics. That is, each message transmitted by the queue is consumed by one consumer only. Hence, if you want to scale up load balancing on the consumer side, all that you need to do is attach extra consumers to the queue. The competing consumer semantics of the JMS queue then automatically ensures that the queue's messages are evenly distributed amongst the attached consumers.
The default behavior of Fuse Message Broker's conduit subscriptions, however, can sometimes be detrimental to load balancing on the consumer side. As described in Conduit subscriptions, conduit subscriptions concentrate all of the subscriptions from a networked broker into a single subscription. For topics this behavior optimizes traffic and has no effect on consumer load. For queues, however, it results in uneven message distribution which can impede consumer load balancing.
Figure 9.1 illustrates how conduit subscriptions can result in uneven message distribution to the consumers of a queue.
Assume that the consumers, C1, C2, and C3, all subscribe to the TEST.FOO
queue. Producer, P, connects to Broker A and sends 12 messages to the TEST.FOO
queue. By default conduit subscriptions are enabled and Broker A sees only a single
subscription from Broker B and a single subscription from consumer C1. So, Broker A sends
messages alternately to C1 and B. Assuming that C1 and B process messages at the same speed,
A sends a total of 6 messages to C1 and 6 messages to B.
Broker B sees two subscriptions, from C2 and C3 respectively. So, Broker B will send messages alternately to C2 and C3. Assuming that both consumers process messages at equal speed, each consumer receives a total of 3 messages.
In the end, the distribution of messages amongst the consumers is 6, 3, 3, which is not optimally load balanced. C1 processes twice as many messages as either C2 or C3.
If you want to improve the load balancing behavior for queues, you can disable conduit
subscriptions by setting the networkConnector element's
conduitSubscriptions to false.
Example 9.1 shows configuration for a network connector
with conduit subscriptions disabled.
Example 9.1. Disabling Conduit Subscriptions
<networkConnectors>
<networkConnector name="linkToBrokerB"
uri="static:(tcp://localhost:61002)"
networkTTL="3"
conduitSubscriptions="false" />
</networkConnectors>![[Warning]](imagesdb/warning.gif) | Warning |
|---|---|
As described in Conduit subscriptions, conduit subscriptions protect against duplicate topic messages. If you are using both queues and topics consider using separate network connectors for queues and topics. See Separate connectors for topics and queues. |
Figure 9.2 illustrates the message flow through a queue with distributed consumers when conduit subscriptions are disabled.
Assume that the consumers, C1, C2, and C3, all subscribe to the TEST.FOO
queue. Producer, P, connects to Broker A and sends 12 messages to the TEST.FOO
queue. With conduit subscriptions disabled, Broker A sees both of the subscriptions on
Broker B and a single subscription from consumer C1. Broker A sends messages alternately
to each of the subscriptions. Assuming that all of the consumers process messages at equal
speeds, C1 receives 4 messages and Broker B receives 8 messages.
Broker B sees two subscriptions, from C2 and C3 respectively. So, Broker B will send messages alternately to C2 and C3. Assuming that both consumers process messages at equal speed, each consumer receives a total of 4 messages.
In the end, the distribution of messages amongst the consumers is 4, 4, 4, which is optimally balanced.
If your brokers need to handle both queues and topics, you might need to disable conduit subscriptions for queues to optimize load balancing, but also enable conduit subscriptions for topics to avoid duplicate topic messages.
Because the conduitSubscriptions attribute
applies simultaneously to queues and topics, you cannot configure this using a single
network connector. It is possible to configure topics and queues differently by using
multiple network connectors: one for queues and another for topics.
Example 9.2 shows how to configure separate
network connectors for topics and queues. The queuesOnly network connector,
which has conduit subscriptions disabled, is equipped with a filter that transmits only
queue messages. The topicsOnly network connector, which has conduit
subscriptions enabled, is equipped with a filter that transmits only topic messages.
Example 9.2. Separate Configuration of Topics and Queues
<networkConnectors> <networkConnector name="queuesOnly" uri="static:(tcp://localhost:61002)" networkTTL="3" conduitSubscriptions="false"> <dynamicallyIncludedDestinations> <queue physicalName=">"/> </dynamicallyIncludedDestinations> </networkConnector> <networkConnector name="topicsOnly" uri="static:(tcp://localhost:61002)" networkTTL="3"> <dynamicallyIncludedDestinations> <topic physicalName=">"/> </dynamicallyIncludedDestinations> </networkConnector> </networkConnectors>
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