When to configure an XA datasource?

If you ever came across this warning message from JBoss, you might wonder what's wrong:

WARN [TxConnectionManager] Prepare called on a local tx. Use of local transactions on a jta transaction with more than one branch may result in inconsistent data in some cases of failure.

It's relevant to JBoss Transaction Management Service for multiple datasources. That is, you have multiple datasources configured and your transactions span multiple data sources. In this case, you need to configure them as XA datasources so that JBoss would not complain.

This is often the case when using Oracle, as you can have multiple users/schema in one database. My test showed this is when XA datasources should be configured.

For instance, we can have two users "BILLING" and "LOG" in one Oracle database. We need to configure two datasources for each of them. If transactions span across these two users, we need to configure xa-datasources:

<xa-datasource>
		<jndi-name>BILLINGDS_XA</jndi-name>
		<track-connection-by-tx>true</track-connection-by-tx>
		<isSameRM-override-value>false</isSameRM-override-value>
		<managedconnectionfactory-class>org.jboss.resource.adapter.jdbc.xa.oracle.XAOracle ManagedConnectionFactory</managedconnectionfactory-class>
		<transaction-isolation></transaction-isolation>
		<xa-datasource-class>oracle.jdbc.xa.client.OracleXADataSource</xa-datasource-class>
		<xa-datasource-property name="URL">jdbc:oracle:thin:@dbserverIP:1521:SID</xa-datasource-property>
		<xa-datasource-property name="User">BILLING</xa-datasource-property>
		<xa-datasource-property name="Password">passwordOfBILLING</xa-datasource-property>
		<min-pool-size>5</min-pool-size>
	  <max-pool-size>10</max-pool-size>
		<exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.Oracle ExceptionSorter</exception-sorter-class-name>
		
	  <mbean code="org.jboss.resource.adapter.jdbc.xa.oracle.Or acleXAExceptionFormatter" name="jboss.jca:service=OracleXAExceptionFormatter">
	    <depends optional-attribute-name="TransactionManagerService">jboss:service=TransactionManager</depends>
  	</mbean>
  </xa-datasource>

<xa-datasource>
		<jndi-name>LOGDS_XA</jndi-name>
		<track-connection-by-tx>true</track-connection-by-tx>
		<isSameRM-override-value>false</isSameRM-override-value>
		<managedconnectionfactory-class>org.jboss.resource.adapter.jdbc.xa.oracle.XAOracle ManagedConnectionFactory</managedconnectionfactory-class>
		<transaction-isolation></transaction-isolation>
		<xa-datasource-class>oracle.jdbc.xa.client.OracleXADataSource</xa-datasource-class>
		<xa-datasource-property name="URL">jdbc:oracle:thin:@dbserverIP:1521:SID</xa-datasource-property>
		<xa-datasource-property name="User">LOG</xa-datasource-property>
		<xa-datasource-property name="Password">passwdOfLOG</xa-datasource-property>
		<min-pool-size>5</min-pool-size>
	  <max-pool-size>10</max-pool-size>
		<exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.Oracle ExceptionSorter</exception-sorter-class-name>
		
	  <mbean code="org.jboss.resource.adapter.jdbc.xa.oracle.Or acleXAExceptionFormatter" name="jboss.jca:service=OracleXAExceptionFormatter">
	    <depends optional-attribute-name="TransactionManagerService">jboss:service=TransactionManager</depends>
  	</mbean>
  </xa-datasource>

Another point is that javax.transaction.UserTransactiion is the JTA api for explicit management of transaction boundaries. This api cannot work properly without JBoss transaction management service turned on. That is, it only works with local-tx-datasource and xa-datasource configurations, not no-tx-datasource. Since it's part of the container's (JBoss for example) Transaction Management Service.