With LockModeType.PESSIMISTIC_READ, JPA acquires a shared pessimistic read lock; if the application later updates that entity and the persistence context is flushed, the provider upgrades the lock to an exclusive pessimistic write lock. PESSIMISTIC_READ is not a synonym of READ, concurrent readers are allowed, and a lock failure typically raises PessimisticLockException rather than TransactionRolledbackException.