Many users see better performance when setting openjpa.ConnectionRetainMode to always. But they might not be aware of the consequences - the EntityManager must be closed in order to release the connection.
In the case of application managed entity managers, the application should always close the EntityManager when it's done. But since this may or may not be obvious, it's a good idea to log an info message.
In the case where the application cannot directly close the EntityManager (e.g. a Container Managed EntityManager), we should log a warning to let users know that each EntityManager may hold on to a connection for a long time.
Unfortunately we can only detect whether the EMF is container managed, not the EM - but some warning is better than none.