Oracle入门教程：Redo 和Undo的区别和联系 详细解释
Oracle入门教程：Redo 和Undo的区别和联系 详细解释
管理目标是避免出现两种错误：
vORA-01650: unable to extend rollback segment
vORA-01555: snapshot too old
管理方式落实为正确配置三个参数和一个还原表空间属性：
UNDO_MANAGEMENT
UNDO_TABLESPACE
UNDO_RETENTION
RETENTION GUARANTEE
9.5 提交和回滚处理
commit操作需要的时间很“平”，与事务的大小没有直接关系。
rollback操作所需的时间与事务所修改的数据量直接相关。
因此在设计事务时，不要考虑事务的大小和多少，而应以所执行的操作是否构成一个逻辑工作单元作依据。
提交前后完成的操作
，
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