Serializable transactions see only those changes that were
committed at the time the transaction began, plus those changes
made by the transaction itself through INSERT, UPDATE, and
DELETE statements. Serializable transactions do not experience
nonrepeatable reads or phantoms.

Oracle隔离级别 : 串行化
1. 串行化隔离的事务只能看到事务开始时提交的数据 , 除了事务内部DML语句更改的数据
2. 串行化隔离的事务不会出现不可重复读取或幻象读取的现象