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From "Dejan Bosanac (Confluence)" <conflue...@apache.org>
Subject [CONF] Apache ActiveMQ > MQTT
Date Thu, 25 Sep 2014 13:51:00 GMT
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                                                            <a href="    https://cwiki.apache.org/confluence/display/~dejanb
" style="color:#326ca6;text-decoration:none;; color: #326ca6; text-decoration: none">Dejan
Bosanac</a> edited the page:
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                                                    <td valign="top" style="font-size:
13px"> <h2 id="email-title-heading" style="font-size: 16px; line-height: 20px; min-height:
20px; margin: 0; padding: 0"> <a href="https://cwiki.apache.org/confluence/display/ACTIVEMQ/MQTT"
style="color: #326ca6; text-decoration: none"> <img class="icon" src="cid:page-icon"
alt="" style="border: 0; padding: 0 5px 0 0; text-align: left; vertical-align: middle" />
<strong style="font-size:16px;line-height:20px;vertical-align:top;">MQTT</strong>
</a> </h2> </td>
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                                                                                <td style="background-color:
#fafafa; padding: 0 0 0 5px; font-size: 12px; text-align: left;; font-size: 13px">xml</td>
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<pre style="font-size: 13px">&lt;transportConnector name=&quot;mqtt&quot;
uri=&quot;mqtt://localhost:1883?transport.defaultKeepAlive=60000&quot;/&gt;</pre>
</td>
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                                                    <h3 id="MQTT-MessagePrefetch" class="diff-block-target
diff-block-context"> <span class="diff-html-added" style="font-size: 100%; background-color:
#ddfade;">Message Prefetch</span> </h3>
                                                    <p class="diff-block-target diff-block-context"
style="font-size: 13px"> <span class="diff-html-added" style="font-size: 100%; background-color:
#ddfade;">When MQTT client connects, it locally create JMS-like consumer to the broker.
By default this consumer is created with prefetch size of 1 (message prefetching is explained
</span><a class="confluence-link unresolved" href="#" style="color: #326ca6; text-decoration:
none"><span class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">here</span></a><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;"> in more details).
Usually, increasing message prefetch size can boost the performance as messages are dispatched
to consumers in batches instead of waiting for the individual acknowledges. To increase prefetch
size, you can use&nbsp;</span><em><span class="diff-html-added" style="font-size:
100%; background-color: #ddfade;">activeMQSubscriptionPrefetch</span></em><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;"> transport
option, like</span> </p>
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#ddfade;"><span class="icon macro-placeholder-icon" style="background-color: ;line-height:
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<pre style="font-size: 13px">
<span class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">&lt;transportConnector</span>
<span class="diff-html-added" id="added-diff-1" style="font-size: 100%; background-color:
#ddfade;">name=&quot;mqtt&quot; uri=&quot;mqtt://localhost:1883?transport.activeMQSubscriptionPrefetch=32766&quot;/&gt;</span>
</pre> </td>
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                                                    <h3 id="MQTT-SubscriptionStrategy"
class="diff-block-target diff-block-context"> <span class="diff-html-added" id="added-diff-2"
style="font-size: 100%; background-color: #ddfade;">Subscription Strategy</span>
</h3>
                                                    <p class="diff-block-target diff-block-context"
style="font-size: 13px"> <span class="diff-html-added" style="font-size: 100%; background-color:
#ddfade;">ActiveMQ is a JMS broker in its core, so there needs to be some mapping between
MQTT subscriptions and JMS semantics. Subscriptions with QoS=0 (At Most Once) are directly
mapped to plain JMS non-persistent topics. For reliable messaging, QoS=1 and QoS=2, by default
subscriptions are transformed to JMS durable topic subscribers. This behaviour is desired
in most scenarios. For some use cases, it is useful to map these subscriptions to </span><a
class="confluence-link unresolved" href="#" style="color: #326ca6; text-decoration: none"><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">virtual topics</span></a><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">. Virtual topics
provide a better scalability and are generally better solution if you want to use you MQTT
subscribers over network of brokers. To change subscription strategy to use virtual topic,
use the following settings:</span> </p>
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diff-block-target diff-block-context" style="background-color: #f0f0f0;border: 1px solid #dddddd;margin:
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<pre style="font-size: 13px">
<span class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">&lt;transportConnector
name=&quot;mqtt&quot; uri=&quot;mqtt://localhost:1883?transport.subscriptionStrategy=mqtt-virtual-topic-subscriptions&quot;/&gt;</span>
</pre> </td>
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                                                    <h3 id="MQTT-RetainedMessages" class="diff-block-target
diff-block-context"> <span class="diff-html-added" style="font-size: 100%; background-color:
#ddfade;">Retained Messages</span> </h3>
                                                    <p class="diff-block-target diff-block-context"
style="font-size: 13px"> <span class="diff-html-added" style="font-size: 100%; background-color:
#ddfade;">If a message has been published with the </span><em><span class="diff-html-added"
style="font-size: 100%; background-color: #ddfade;">retain</span></em><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;"> flag set,
then the message will be 'remembered' by the topic so that if a new subscription arrives,
the last retained message is sent to the subscription. Underneath, the broker uses </span><a
class="confluence-link unresolved" href="#" style="color: #326ca6; text-decoration: none"><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">retained message
subscription recovery policy</span></a><span class="diff-html-added" style="font-size:
100%; background-color: #ddfade;"> to retain messages with&nbsp;</span><em><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;">ActiveMQ.Retain</span></em><span
class="diff-html-added" style="font-size: 100%; background-color: #ddfade;"> property set.
During the message conversion, MQTT messages with retain flag become JMS message with the
</span><em><span class="diff-html-added" style="font-size: 100%; background-color:
#ddfade;">ActiveMQ.Retain&nbsp;</span></em><span class="diff-html-added"
style="font-size: 100%; background-color: #ddfade;">property set and retained by the broker.</span>
</p>
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