188 lines
7.6 KiB
HTML
188 lines
7.6 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ Artemis Paging Example</title>
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<link rel="stylesheet" type="text/css" href="../../../common/common.css" />
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<link rel="stylesheet" type="text/css" href="../../../common/prettify.css" />
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<script type="text/javascript" src="../../../common/prettify.js"></script>
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</head>
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<body onload="prettyPrint()">
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<h1>Paging Example</h1>
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<pre>To run the example, simply type <b>mvn verify</b> from this directory, <br>or <b>mvn -PnoServer verify</b> if you want to start and create the server manually.</pre>
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<p>This example shows how ActiveMQ Artemis would avoid running out of memory resources by paging messages.</p>
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<p>A maxSize can be specified per Destination via the destinations settings configuration file (broker.xml).</p>
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<p>When messages routed to an address exceed the specified maxSize the server will begin to write messages to the file
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system, this is called paging. This will continue to occur until messages have been delivered to consumers and subsequently
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acknowledged freeing up memory. Messages will then be read from the file system , i.e. depaged, and routed as normal. </p>
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<p>Acknowledgement plays an important factor on paging as messages will stay on the file system until the memory is released
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so it is important to make sure that the client acknowledges its messages.</p>
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<h2>Example step-by-step</h2>
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<ol>
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<li>First we need to get an initial context so we can look-up the JMS connection factory and destination objects from JNDI. This initial context will get it's properties from the <code>client-jndi.properties</code> file in the directory <code>../common/config</code></li>
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<pre class="prettyprint">
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<code>InitialContext initialContext = getContext();</code>
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</pre>
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<li>We look-up the JMS connection factory object from JNDI</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>We look-up the JMS queue object from JNDI. pagingQueue is configured to hold a very limited number of bytes in memory</li>
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<pre class="prettyprint">
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<code>Queue pageQueue = (Queue) initialContext.lookup("/queue/pagingQueue");</code>
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</pre>
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<li>We look-up the JMS queue object from JNDI.</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>We 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>We create a JMS session. The session is created as non transacted. We will use client acknowledgement on this example.</li>
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<pre class="prettyprint">
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<code>Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);</code>
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</pre>
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<li>Create a JMS Message Producer for pageQueueAddress</li>
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<pre class="prettyprint"><code>
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MessageProducer pageMessageProducer = session.createProducer(pageQueue);
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</pre></code>
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<li>We don't need persistent messages in order to use paging. (This step is optional)</li>
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<pre class="prettyprint"><code>
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pageMessageProducer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
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</pre></code>
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<li>Create a Binary Bytes Message with 10K arbitrary bytes</li>
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<pre class="prettyprint"><code>
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BytesMessage message = session.createBytesMessage();
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message.writeBytes(new byte[10 * 1024]);
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</pre></code>
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<li>Send only 20 messages to the Queue. This will be already enough for pagingQueue. Look at ./paging/config/activemq-queues.xml for the config.</li>
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<pre class="prettyprint"><code>
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for (int i = 0; i < 20; i++)
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{
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pageMessageProducer.send(message);
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}
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</pre></code>
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<li>Create a JMS Message Producer</li>
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<pre class="prettyprint"><code>
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MessageProducer messageProducer = session.createProducer(queue);
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</pre></code>
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<li>We don't need persistent messages in order to use paging. (This step is optional)</li>
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<pre class="prettyprint"><code>
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messageProducer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
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</pre></code>
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<li>Send the message for about 30K, which should be over the memory limit imposed by the server</li>
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<pre class="prettyprint"><code>
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for (int i = 0; i < 30000; i++)
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{
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messageProducer.send(message);
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}
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</pre></code>
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<li>if you pause the example here, you will several files under ./build/data/paging</li>
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<pre class="prettyprint"><code>
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// Thread.sleep(30000); // if you want to just our of curiosity, you can sleep here and inspect the created files just for
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</pre></code>
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<li>Create a JMS Message Consumer</li>
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<pre class="prettyprint"><code>
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MessageConsumer messageConsumer = session.createConsumer(queue);
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</pre></code>
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<li>Start the JMS Connection. This step will activate the subscribers to receive messages.</li>
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<pre class="prettyprint"><code>
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connection.start();
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</pre></code>
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<li>Receive the messages. It's important to ACK for messages as ActiveMQ Artemis will not read messages from paging until messages are ACKed</li>
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<pre class="prettyprint"><code>
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for (int i = 0; i < 30000; i++)
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{
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message = (BytesMessage)messageConsumer.receive(1000);
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if (i % 1000 == 0)
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{
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System.out.println("Received " + i + " messages");
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message.acknowledge();
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}
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}
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</pre></code>
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<li>Receive the messages from the Queue names pageQueue. Create the proper consumer for that.</li>
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<pre class="prettyprint"><code>
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messageConsumer.close();
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messageConsumer = session.createConsumer(pageQueue);
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for (int i = 0; i < 20; i++)
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{
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message = (BytesMessage)messageConsumer.receive(1000);
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System.out.println("Received message " + i + " from pageQueue");
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message.acknowledge();
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}
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</pre></code>
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<li>And finally, <b>always</b> remember to close your JMS connections and resources after use, in a <code>finally</code> block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects</li>
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<pre class="prettyprint">
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<code>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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</body>
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</html>
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