Working with stateless session in hibernate and jpa

When doing heavy read-only operations in with the database it can be a good idea to take advantage of using Hibernate's Stateless Session

As it name indicates this session does not keep state of the entities that it retrieves from the database and so it bypasses the L1 and L2 cache

This can have significant performance impact on heavy DBA read operations (since the state of the entities is not bet tracked)

@Component
@Scope("prototype")
public class SomeJpaService {

public static final int SCROLL_STEP = 1000;

     @PersistenceContext
     private EntityManager entityManager;


    
     public void doInStatelessSession(){

       LOGGER.info("ABOUT to perform Heavy read operation on DB");

       StatelessSession statelessSession = entityManager.unwrap(Session.class).getSessionFactory().openStatelessSession();

        try (ScrollableResults r = statelessSession
                .createQuery("SELECT c FROM Order c")
                .setReadOnly(true)
                .setCacheable(false)
                .scroll()) {// create the scrollable results with a try/close resources block

            while (r.scroll(SCROLL_STEP)) {
                 Order o = (Order) r.get(0);
                //perform some operation on object
              
            }
        }      



        LOGGER.info("FINISHED heavy read operation");

        statelessSession.close();
   }


}

There's however a few caveats with this approach :

• Collections cannot be fetched on stateless sessions
• Because of the stateless nature of the session this can only be used on read-only operations

EclipseLink (JPA) Spring - No persistence exception translators exception

I recently stumbled upon a Spring Exception while working with Spring Data JPA and attempting to deploy a WAR file on glassfish. I have a JTA datasource defined in my glassfish which is used by Spring (through JNDI) to instantiate my entity manager. The JPA configuration was pretty straight forward but every time I tried to deploy the app on Glassfish I stumbled upon the error :

org.springframework.beans.factory.BeanCreationException: 
Error creating bean with name 
'org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor#0': 
Initialization of bean failed; 
nested exception is java.lang.IllegalStateException: 
No persistence exception translators found in bean factory.
Cannot perform exception translation.

Apparently when using Hibernate there is an easy fix for this : Declaring a Hibernate Exception Translator in the spring beans config file :

When using EclipseLink though this doesn't work... So I looked for implementations of the spring interface :

org.springframework.dao.support.PersistenceExceptionTranslator 

And found out that there is not an EclipseLinkExceptionTranslator (as for Hibernate) but there is a EclipseLinkJpaDialect

   org.springframework.orm.jpa.vendor.EclipseLinkJpaDialect

That implements the interface so I created a bean in the spring configuration file and I was able to deploy the app on the glassfish.