Thanks for help. If one peristence unit is mapped to many data sources(with same tables), is there any problems with Hibernate caching? We tried the following in a stateless session bean: Map configOverrides = new HashMap(); EntityManagerFacotry emf = Persistence.createEntityManagerFactory("unit1", configOverrides); But got exception: javax.persistence.PersistenceException: [PersistenceUnit: unit1] Unable to build EntityManagerFactory <persistence-unit name="unit1"> | <jta-data-source>java:/dataSource1</jta-data-source> | | <properties> | <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/> | <property name="hibernate.hbm2ddl.auto" value="update"/> | <property name="hibernate.show_sql" value="false"/> | </properties> | </persistence-unit> But the following works. @PersistenceContext (unitName="unit1") | protected EntityManager em; What is the right way to create entityManagerFactory? Thanks! Dave View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4266927#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...