Feedback is welcome on a proposed change for HHH-7018 https://github.com/scottmarlow/hibernate-orm/commit/007e7f17eed10c6c1db55... When we serialize the EntityManagerFactory in 4.0.0, there can be nonserializeable objects in the EMF configuration properties (e.g. JTA_PLATFORM, datasource, other stuff). In most cases, we will have a session factory name (preferred) or persistence unit name to uniquely identify the EntityManagerFactory. In 4.0.1, during serialization, we only serialize the (hopefully) unique name. If a duplicate EntityManagerFactory is created (by name), no immediate error is given, instead we only give an error later when deserializing the EMF. The HibernateException thrown during deserialization will look like: "registry contains more than one (" + entityManagerFactorySet.size()+ ") entity manager factories: " + name If that causes issues for any application, the SESSION_FACTORY_NAME can be passed in from the troubled application (possibly with SESSION_FACTORY_NAME_IS_JNDI set to false but true is also fine). For the 4.1 release, I would like to take this one step further. The above changes, only were made for EntityManager serialization of the EM to EMF reference. The next step is to apply the same change to the EMF readObject/writeObject, such that we also allow the EMF to be serialized when it contains nonserializable objects. This also simplifies the EM serialization, as it can just use default serialization for the EMF. The proposed commit (to be fixed in 4.1) is at https://github.com/scottmarlow/hibernate-orm/commit/007e7f17eed10c6c1db55.... Feedback on the change is welcome (we are building 4.1 final middle of this week). Scott