I'd also like to add that I probably would suggest that long-running transactions probably be batched operations using small transaction-based chunks rather than a single massive transaction. This allows database resources to not be locked indefinitely and scales well in high concurrency situations. Not only that, but it keeps the audit work units flushed with each transaction commit too.

final List<List<Entity>> partitionedList = ListUtils.partition( massiveList, 50 ); // split a list of 1000 entities into small chunks of 50.
for ( List<Entity> subList : partitionedList ) {
  entityManager.getTransaction().begin();
  for ( Entity entity : subList ) {
    entityManager.persist( entity );
  }
  entityManager.getTransaction().commit();
}