java什么是JPA悲观显式@Lock用例（而仅仅@Transactional不是选项）？

Question

我对JPA和DB锁（乐观型和悲观型）和事务、它们的工作原理和保证有一定的了解

A TransactionRequiredException is thrown if there is no active transaction when lock is called because explicit locking requires an active transaction.

所以我的问题是：当事务（JPA案例中的@Transactional）不够用，需要显式使用@Lock（LockModeType.epositic_*）时，用例是什么

我对精确的悲观锁感兴趣，并期望有如下用例：

Alice and Bob simultaneously edit page on wikipedia, Alice start to edit a page and locked it..........................and transaction is redundant/not enough/low performance in this case ............................

我不期望：

1. Use @Lock when you need just a lock

2. Use optimistic lock its better

3. Locking is used to prevent dirty reads (reading data that hasn't been committed) and non-repeatable reads (reading data that gets deleted by another transaction before the one reading is finished).