So after moving from 3.3.1.GA to 5.1.0 I now have EntityExistExceptions

Is there any reason between these releases where I'd see this occuring?

FWIW the problem appears to be on the identifier associated with a child object getting associated with the persistence context when it's already been associated with the same identifier for another object.

Is GenerationType.SEQUENCE still based on HILO?

So is the GenerationType.SEQUENCE still a HILO based generator?

I show it to be this SequenceStyleGenerator and it doesn't look like it uses HiLo from a sequence with a non 1 cache size and a 1 increment by.

Ok so my problem was due to the changes to the sequence generators so my earlier gut impression on HILO was in fact correct.

for now I've fixed it by adding the following to persistence.xml

<property name="hibernate.id.new_generator_mappings" value ="false"/>

This keeps using the older generators.