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<h1>JMS Message Consumer Rate Limiting</h1>
<p>With HornetQ you can specify a maximum consume rate at which a JMS MessageConsumer will consume messages.
This can be specified when creating or deploying the connection factory. See <code>hornetq-jms.xml</code></p>
<p>If this value is specified then HornetQ will ensure that messages are never consumed at a rate higher than
the specified rate. This is a form of consumer <i>throttling</i>.</p>
<h2>Example step-by-step</h2>
<p>In this example we specify a <code>consumer-max-rate</code> of <code>10</code> messages per second in the <code>hornetq-jms.xml</code>
file when deploying the connection factory:</p>
<pre class="prettyprint">
<code>
<connection-factory name="ConnectionFactory">
<connector-ref connector-name="netty-connector"/>
<entries>
<entry name="ConnectionFactory"/>
</entries>
<!-- We limit consumers created on this connection factory to consume messages at a maximum rate
of 10 messages per sec -->
<consumer-max-rate>50</producer-max-rate>
</connection-factory>
</code>
</pre>
<p>We then simply consume as many messages as we can in 10 seconds and note how many messages are actually consumed.</p>
<p>We note that the number of messages consumed per second never exceeds the specified value of <code>10</code> messages per second.</p>
<p><i>To run the example, simply type <code>mvn verify</code> from this directory</i></p>
<ol>
<li>Create an initial context to perform the JNDI lookup.</li>
<pre class="prettyprint">
<code>initialContext = getContext(0);</code>
</pre>
<li>Perfom a lookup on the queue</li>
<pre class="prettyprint">
<code>Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");</code>
</pre>
<li>Perform a lookup on the Connection Factory</li>
<pre class="prettyprint">
<code>ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");</code>
</pre>
<li>Create a JMS Connection</li>
<pre class="prettyprint">
<code>connection = cf.createConnection();</code>
</pre>
<li>Create a JMS Session</li>
<pre class="prettyprint">
<code>Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
</pre>
<li>Create a JMS MessageProducer</li>
<pre class="prettyprint">
<code>MessageProducer producer = session.createProducer(queue);</code>
</pre>
<li>Create a JMS MessageConsumer</li>
<pre class="prettyprint">
<code>MessageConsumer consumer = session.createConsumer(queue);</code>
</pre>
<li>Start the connection</li>
<pre class="prettyprint">
<code>
connection.start();
</code>
</pre>
<li>Send a bunch of messages</li>
<pre class="prettyprint">
<code>
final int numMessages = 150;
for (int i = 0; i < numMessages; i++)
{
TextMessage message = session.createTextMessage("This is text message: " + i);
producer.send(message);
}
</code>
</pre>
<li>Consume as many messages as we can in 10 seconds</li>
<pre class="prettyprint">
<code>
final long duration = 10000;
int i = 0;
long start = System.currentTimeMillis();
while (System.currentTimeMillis() - start <= duration)
{
TextMessage message = (TextMessage)consumer.receive(2000);
if (message == null)
{
return false;
}
i++;
}
long end = System.currentTimeMillis();
double rate = 1000 * (double)i / (end - start);
System.out.println("We consumed " + i + " messages in " + (end - start) + " milliseconds");
System.out.println("Actual consume rate was " + rate + " messages per second");
</code>
</pre>
<li>This should produce output something like:</li>
<pre class="prettyprint">
<code>
[java] Sent messages
[java] Will now try and consume as many as we can in 10 seconds ...
[java] We consumed 100 messages in 10001 milliseconds
[java] Actual consume rate was 9.99900009999 messages per second
</code>
</pre>
<li>Be sure to close our resources!</li>
<pre class="prettyprint">
<code>
finally
{
if (initialContext != null)
{
initialContext.close();
}
if (connection != null)
{
connection.close();
}
}</code>
</pre>
</ol>
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