The various HashMap<Class,Callback[]> managed by CallbackRegistryImpl have been identified as having a disproportionate cost to efficiency, compared to other areas.

It would seem worthwhile to explore some options, perhaps:

1. use a different data structure to maintain the mapping
2. store some very hot data within the EntityPersister

And not limited to these ideas.

This in particular shows as very hot in a benchmark performing many updates:

{{Object java.util.HashMap.get(Object) 97 62.6 %}}
{{ void org.hibernate.jpa.event.internal.CallbackRegistryImpl.postUpdate(Object) 24 15.5 %}}