2014-10-31 06:20:28 -04:00
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2014-11-19 03:44:57 -05:00
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<title>ActiveMQ No Consumer Buffering Example</title>
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2014-10-31 06:20:28 -04:00
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<h1>No Consumer Buffering Example</h1>
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2014-11-19 03:44:57 -05:00
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<p>By default, ActiveMQ consumers buffer messages from the server in a client side buffer
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before actual delivery actually occurs.</p>
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<p>This improves performance since otherwise every time you called receive() or had processed the last
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message in a MessageListener onMessage() method, the ActiveMQ client would have to go the
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server to request the next message involving a network round trip for every message reducing performance.</p>
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<p>Therefore, by default, ActiveMQ pre-fetches messages into a buffer on each consumer. The total maximum size of
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messages in bytes that will be buffered on each consumer is determined by the <code>consumer-window-size</code>
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parameter on the connection factory.</p>
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<p>In some cases it is not desirable to buffer any messages on the client side consumer.</p>
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<p>An example would be an order queue which had multiple consumers that processed orders from the queue.
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Each order takes a significant time to process, but each one should be processed in a timely fashion.</p>
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<p>If orders were buffered in each consumer, and a new consumer was added that consumer would not be able
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to process orders which were already in the client side buffer of another consumer.</p>
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<p>To turn off client side buffering of messages, set <code>consumer-window-size</code> to zero.</p>
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2014-11-19 03:44:57 -05:00
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<p>With ActiveMQ you can specify a maximum consume rate at which a JMS MessageConsumer will consume messages.
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This can be specified when creating or deploying the connection factory. See <code>hornetq-jms.xml</code></p>
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<h2>Example step-by-step</h2>
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<p>In this example we specify a <code>consumer-window-size</code> of <code>0</code> bytes in the <code>hornetq-jms.xml</code>
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file when deploying the connection factory:</p>
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<pre class="prettyprint">
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<code>
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<connection-factory name="ConnectionFactory">
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<connector-ref connector-name="netty-connector"/>
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<entries>
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<entry name="ConnectionFactory"/>
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</entries>
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<!-- We set the consumer window size to 0, which means messages are not buffered at all
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on the client side -->
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<consumer-window-size>0</consumer-window-size>
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</connection-factory>
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</code>
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</pre>
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<p>We create a consumer on a queue and send 10 messages to it. We then create another consumer on
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the same queue.</p>
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<p>We then consume messages from each consumer in a semi-random order. We note that the messages
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are consumed in the order they were sent.</p>
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<p>If the messages had been buffered in each consumer they would not be available to be consumed
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in an order determined afer delivery.</p>
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<p><i>To run the example, simply type <code>mvn verify</code> from this directory</i></p>
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<ol>
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<li>Create an initial context to perform the JNDI lookup.</li>
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<pre class="prettyprint">
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<code>initialContext = getContext(0);</code>
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</pre>
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<li>Perfom a lookup on the queue</li>
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<pre class="prettyprint">
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<code>Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");</code>
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</pre>
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<li>Perform a lookup on the Connection Factory</li>
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<pre class="prettyprint">
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<code>ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");</code>
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</pre>
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<li>Create a JMS Connection</li>
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<pre class="prettyprint">
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<code>connection = cf.createConnection();</code>
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</pre>
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<li>Create a JMS Session</li>
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<pre class="prettyprint">
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<code>Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
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</pre>
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<li>Create a JMS MessageProducer</li>
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<pre class="prettyprint">
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<code>MessageProducer producer = session.createProducer(queue);</code>
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</pre>
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<li>Create a JMS MessageConsumer</li>
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<pre class="prettyprint">
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<code>MessageConsumer consumer1 = session.createConsumer(queue);</code>
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</pre>
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<li>Start the connection</li>
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<pre class="prettyprint">
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<code>
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connection.start();
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</code>
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</pre>
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<li>Send 10 messages to the queue</li>
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<pre class="prettyprint">
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<code>
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final int numMessages = 10;
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for (int i = 0; i < numMessages; i++)
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{
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TextMessage message = session.createTextMessage("This is text message: " + i);
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producer.send(message);
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}
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</code>
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</pre>
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<li>Create another JMS MessageConsumer on the same queue.</li>
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<pre class="prettyprint">
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<code>MessageConsumer consumer2 = session.createConsumer(queue);</code>
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</pre>
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<li>Consume three messages from consumer2</li>
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<pre class="prettyprint">
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<code>
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for (int i = 0; i < 3; i++)
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{
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TextMessage message = (TextMessage)consumer2.receive(2000);
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System.out.println("Consumed message from consumer2: " + message.getText());
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}
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</code>
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</pre>
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<li>Consume five messages from consumer1</li>
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<pre class="prettyprint">
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<code>
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for (int i = 0; i < 5; i++)
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{
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TextMessage message = (TextMessage)consumer1.receive(2000);
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System.out.println("Consumed message from consumer1: " + message.getText());
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}
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</code>
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</pre>
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<li>Consume two more messages from consumer2</li>
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<pre class="prettyprint">
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<code>
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for (int i = 0; i < 2; i++)
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{
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TextMessage message = (TextMessage)consumer1.receive(2000);
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System.out.println("Consumed message from consumer2: " + message.getText());
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}
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</code>
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</pre>
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<li>Be sure to close our resources!</li>
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<pre class="prettyprint">
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<code>
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finally
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{
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if (initialContext != null)
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{
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initialContext.close();
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}
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if (connection != null)
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{
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connection.close();
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}
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}</code>
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</pre>
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</ol>
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<h2>More information</h2>
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<ul>
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<li>User Manual's <a href="../../../docs/user-manual/en/html_single/index.html#flow-control.consumer.window">Consumer Window-Based Flow Control chapter</a></li>
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</ul>
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</body>
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</html>
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