I'm getting the following error:

2010-07-14 11:04:45,939 ERROR pool-2-thread-2 ORA-00060: deadlock detected while waiting for resource

2010-07-14 11:04:45,939 WARN pool-2-thread-2 SQL Error: 60, SQLState: 61000
2010-07-14 11:04:45,939 ERROR pool-2-thread-2 ORA-00060: deadlock detected while waiting for resource

2010-07-14 11:04:45,940 ERROR pool-2-thread-2 Could not synchronize database state with session
org.hibernate.exception.LockAcquisitionException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:112)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:275)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:263)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:184)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventL
istener.java:321)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1206)
at org.hibernate.impl.SessionImpl.forceFlush(SessionImpl.java:1227)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:1
88)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListene
r.java:144)
at org.hibernate.ejb.event.EJB3MergeEventListener.saveWithGeneratedId(EJB3MergeEventListener.java
:62)
at org.hibernate.event.def.DefaultMergeEventListener.mergeTransientEntity(DefaultMergeEventListen
er.java:313)
at org.hibernate.event.def.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.
java:282)
at org.hibernate.event.def.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.j
ava:396)
at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:234)
at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:84)
at org.hibernate.impl.SessionImpl.fireMerge(SessionImpl.java:859)
at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:843)
at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:847)
at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:682)

I have a parent entity with a one-to-many relationship with a child entity. I'm trying to use the delete_orphan option too.
When running multi-threaded, each thread getting a new EntityManager from the EntityManagerFactory, I get the above error.
Inside a transaction, My code
- queries the parent object and then calls the remove for that object
- Creates a new parent object and adds children
- commits the transaction.
Its works fine single-threaded but I don't understand why it should be different multi-threaded because the parents are all unique.

Any help greatly appreciated.

Gary