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<h1>Last Resource Commit optimization</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 database using Last Resource Commit this scenario is 100% safe, otherwise not.</p></td></tr></table>

<p>In theory, only databases supporting XA and providing a <code>javax.sql.XADataSource</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 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 datasource emulating XA with Last Resource Commit participating in a transaction. If it happens that you're trying to use a second emulating datasource 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>PoolingDataSource</code> using the <a href="http://btm.codehaus.org/api/1.2/bitronix/tm/resource/jdbc/lrc/LrcXADataSource.html">bitronix.tm.resource.jdbc.lrc.LrcXADataSource</a> as the <code>XADataSource</code> implementation.</p>

<p>Here's an example of code configuring a HSQLDB 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>
PoolingDataSource myDataSource = new PoolingDataSource();
myDataSource.setClassName("bitronix.tm.resource.jdbc.lrc.LrcXADataSource");
myDataSource.setUniqueName("hsqldb");
myDataSource.setMaxPoolSize(5);
myDataSource.setAllowLocalTransactions(true);
myDataSource.getDriverProperties().setProperty("driverClassName", "org.hsqldb.jdbcDriver");
myDataSource.getDriverProperties().setProperty("url", "jdbc:hsqldb:/the/db/path");
myDataSource.getDriverProperties().setProperty("user", "sa");
myDataSource.getDriverProperties().setProperty("password", "theSaPassword");
</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.jdbc.lrc.LrcXADataSource
resource.ds.uniqueName=hsqldb
resource.ds.maxPoolSize=5
resource.ds.allowLocalTransactions=true
resource.ds.driverProperties.driverClassName=org.hsqldb.jdbcDriver
resource.ds.driverProperties.url=jdbc:hsqldb:/the/db/path
resource.ds.driverProperties.user=sa
resource.ds.driverProperties.password=theSaPassword
</pre></td></tr></table>

<table class="wysiwyg-macro" data-macro-name="warning" data-macro-parameters="title=Mandatory pool settings" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e3dhcm5pbmc6dGl0bGU9TWFuZGF0b3J5IHBvb2wgc2V0dGluZ3N9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="RICH_TEXT"><tr><td class="wysiwyg-macro-body">
<p>The LRC implementation relies on the <code>useTmJoin</code> and <code>deferConnectionRelease</code> pool properties which must always be <strong>true</strong> (the default value).<br />
Do not change these properties as this could force the transaction manager to reject the resource or worse, cause inconsistencies during commit phase.</p></td></tr></table>
<p><img class="confluence-embedded-image confluence-external-resource" src="http://www.bitronix.be/images/shim.gif" data-image-src="http://www.bitronix.be/images/shim.gif"></p>