EJB 3.0 and JTA (Distributed transactions)

Question

hi, first of all sorry for my english.
then :)
i'm working with JBoss Aplication Server an Oracle DataBase using EJB 3.0
i have no problem before ... but now i want work with multiple database and i wand to manage transactions ... how i understand JTA (Java Transaction Api) is a technology for it.
i think that i need two datasource file for example oracle-xa-ds.xml and postgres-ds.xml
<datasources>
  <xa-datasource>
    <jndi-name>XAOracleDS</jndi-name>
    <track-connection-by-tx/>
    <isSameRM-override-value>false</isSameRM-override-value>    <xa-datasource-class>oracle.jdbc.xa.client.OracleXADataSource</xa-datasource-class>
    <xa-datasource-property name="URL">jdbc:oracle:thin:@192.9.200.177:1521:devnbtwo</xa-datasource-property>
    <xa-datasource-property name="User">paata</xa-datasource-property>
    <xa-datasource-property name="Password">1982226</xa-datasource-property>   <exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.OracleExceptionSorter</exception-sorter-class-name>
    <no-tx-separate-pools/>
      <metadata>
         <type-mapping>Oracle9i</type-mapping>
      </metadata>
  </xa-datasource>
  <mbean code="org.jboss.resource.adapter.jdbc.vendor.OracleXAExceptionFormatter"
         name="jboss.jca:service=OracleXAExceptionFormatter">
    <depends optional-attribute-name="TransactionManagerService">jboss:service=TransactionManager</depends>
  </mbean>
</datasources>
<datasources>
  <local-tx-datasource>
    <jndi-name>PostgresDS</jndi-name>
   <connection-url>jdbc:postgresql://localhost:5432/Test</connection-url>
    <driver-class>org.postgresql.Driver</driver-class>
    <user-name>postgres</user-name>
    <password>1982226</password>
        <new-connection-sql>select 1</new-connection-sql>
      <metadata>
         <type-mapping>PostgreSQL 7.2</type-mapping>
      </metadata>
  </local-tx-datasource>
</datasources>and i dont know what should i do in my persistance.xml file ..... when i was working with single database my persistance.xml file was working
<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
     version="1.0">     
     <persistence-unit name="Oracle" transaction-type="JTA">
          <jta-data-source>java:/XAOracleDS</jta-data-source>
          <class>com.magti.businesslayer.ejb3entity.Group</class>
          <class>com.magti.businesslayer.ejb3entity.Student</class>
          <properties>
               <property name="hibernate.dialect" value="org.hibernate.dialect.OracleDialect"/>
               <property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver"/>
               <property name="hibernate.connection.url" value="jdbc:oracle:thin:@192.9.200.177:1521:devnbtwo"/>
               <property name="hibernate.connection.username" value="paata"/>
               <property name="hibernate.connection.password" value="1982226"/>
               <property name="hibernate.default_schema" value="PAATA"/>
          </properties>
     </persistence-unit>     
</persistence>but then i added anothe unit for second database and i get error
     <persistence-unit name="PostgreSql" transaction-type="JTA">
          <jta-data-source>java:/PostgresDS</jta-data-source>
          <class>com.magti.businesslayer.ejb3entity.Group</class>
          <class>com.magti.businesslayer.ejb3entity.Student</class>
          <properties>
               <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
               <property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
               <property name="hibernate.connection.url" value="jdbc:postgresql://localhost:5432/Test"/>
               <property name="hibernate.connection.username" value="postgres"/>
               <property name="hibernate.connection.password" value="1982226"/>
               <property name="hibernate.default_schema" value="postgres"/>
          </properties>
     </persistence-unit>     i don't know how i resolve it .
i can't find any simple exaplme about distributed transactions on net ...
can anybody help me ....
thanks.

Answer 1

Check this one:
http://www.webagesolutions.com/knowledgebase/javakb/jkb005/index.html