Description: When shutting down servers, sessions are not updated. If the primary and secondary servers of a session are shut down with no session updates, the session will be lost. Turning on PersistSessionsOnShutdown will save any active sessions to the database specified in {@link ClusterMBean#getDataSourceForSessionPersistence()} when a server is shutdown. The sessions will not be written at any other time. (For example, they are not saved via this mechanism if there is a server crash.) This attribute is applicable both to session persistence on server shutdown or session persistence across a WAN. Rolling upgrade can potential have a bad interaction with traditional in-memory session replication. As managed servers are shutdown and upgraded, in-memory servlet sessions will be lost if both primary and secondary are rebooted before a new request arrives for the session.