I am learning JPA and have one question:

In which situations we need more than one EntityManager in our application?

The two situations that I am aware of are as follows:

• When our application is a multi-threaded application and more than one thread needs JPA transaction because EntityManager is not thread-safe and we need one EntityManager per thread.

• When any of the thread needs multiple concurrent transactions, we need more than one EntityManager in that thread because there is one-to-one relationship between EntityManager and EntityTransaction.

Q1. Are there any other situations when we need more than one EntityManager?

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Q2. Upto my understanding, there should be only one EntityManagerFactory per Persitence Unit. Am I correct? If not, then what are those situations when we need multiple EntityManagerFactory per Persistence Unit?