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<h1>Last Resource Commit optimization for JMS</h1>

<table class="wysiwyg-macro" data-macro-name="note" data-macro-parameters="title=Be Careful" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e25vdGU6dGl0bGU9QmUgQ2FyZWZ1bH0&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="RICH_TEXT"><tr><td class="wysiwyg-macro-body"><p>There is one caveat with Last Resource Commit. There is a small chance that a transaction ends up with inconsistent results across participating resources if BTM crashes while a transaction is in-flight. The chance is small but it exists so be careful when using that feature. This is in <em>no way</em> a limitation of BTM but of the concept itself.</p>

<p>Please note that if you only intend to run transactions against a single JMS server using Last Resource Commit this scenario is 100% safe, otherwise not.</p></td></tr></table>

<p>In theory, only JMS servers supporting XA and providing a <code>javax.jms.XAConnectionFactory</code> implementation can be used with transaction managers. In practice, there is a way around this limitation.</p>

<p>The Last Resource Commit optimization (sometimes referred to as Last Resource Gambit or Last Agent optimization) allows a single non-XA resource (JMS server or database) to participate in a XA transaction by cleverly ordering the resources.</p>

<table class="wysiwyg-macro" data-macro-name="info" data-macro-parameters="title=Maximum one non-XA resource" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2luZm86dGl0bGU9TWF4aW11bSBvbmUgbm9uLVhBIHJlc291cmNlfQ&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="RICH_TEXT"><tr><td class="wysiwyg-macro-body"><p>There can be at most one resource emulating XA with Last Resource Commit participating in a transaction. If it happens that you're trying to use a second emulating resource while one has already been used, BTM will throw an exception. Again, this is not a limitation of BTM but of the concept itself.</p></td></tr></table>

<p>To enable it, you just have to create a <code>PoolingConnectionFactory</code> using the <a href="http://btm.codehaus.org/api/2.0.1/bitronix/tm/resource/jms/lrc/LrcXAConnectionFactory.html">bitronix.tm.resource.jms.lrc.LrcXAConnectionFactory</a> as the <code>XAConnectionFactory</code> implementation.</p>

<p>Here's an example of code configuring a ActiveMQ datasource:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
PoolingConnectionFactory myConnectionFactory = new PoolingConnectionFactory();
myConnectionFactory.setClassName("bitronix.tm.resource.jms.lrc.LrcXAConnectionFactory");
myConnectionFactory.setUniqueName("amq-lrc");
myConnectionFactory.setMaxPoolSize(5);
myConnectionFactory.getDriverProperties().setProperty("connectionFactoryClassName", "org.apache.activemq.ActiveMQConnectionFactory");
myConnectionFactory.getDriverProperties().setProperty("properties.brokerUrl", "tcp://localhost:61616");
</pre></td></tr></table>

<p>and the same example viewed as a Resource Loader configuration</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
resource.ds.className=bitronix.tm.resource.jms.lrc.LrcXAConnectionFactory
resource.ds.uniqueName=amq-lrc
resource.ds.maxPoolSize=5
resource.ds.driverProperties.connectionFactoryClassName=org.apache.activemq.ActiveMQConnectionFactory
resource.ds.driverProperties.properties.brokerUrl=tcp://localhost:61616
</pre></td></tr></table>