Unique-Constraint Exceptions when sending messages from a Message-Driven-Bean(MDB) into the Database

Issue

Consider the following scenario:

• A Message-Driven-Bean (MDB) with 20 parallel instances is reading from a JMS queue
• The payload of the message is mapped to the entity model
  using Apache Deltaspike and JBoss-Hibernate.
• A message can either be new (a) or already exists (b). In case of (a) the new message gets inserted into the Database, else it gets merged.
• The check regarding (a) and (b) is performed on the Dataobject (DAO) on some Custom ID extracted from the message.
• In the Database a Unique-Constraint on the ID has been defined.

Under load the following exception occurred:

org.hibernate.engine.transaction.synchronization.internal.SynchronizationCallbackCoordinatorNonTrackingImpl.beforeCompletion(SynchronizationCallbackCoordinatorNonTrackingImpl.java:109)
Caused by: java.sql.SQLIntegrityConstraintViolationException: ORA-00001: unique constraint (INDEX) violated
  at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:450)
        at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:399)
        at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:1017)
        at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:655)

The issue is that the exception cannot be handled and a retry is not possible.