oracle(十二)redo 与 undo
2013-09-24 15:42
387 查看
1.undo:回滚未提交的事务。未提交前,内存不够用时,DBWR将脏数据写入数据文件中,以腾出内存空间。 这就是undo存在的原因。
redo:恢复所有已提交的事务
2.实例失败(如主机掉电)可能出现的情况:
(1)已提交的事务只写到了online redo log,但没有写到数据文件中。(commit时,oracle先调用LGWR,再调用DBWR)
(2)没提交的数据写到了数据文件中。(内存不够用)
3.实例恢复的两个阶段
(1)rolling forward (Cache Recovery) :after rolling forward,the data files contain all committed changes recorded in the online redo log file.
These files could also contain uncommitted changes that were either saved to the data files before the failure.
(2)rolling back ( Transaction Recovery):any changes that were not committed must be undone.
4.redo 会把undo tabaleSpace或undo segment中的数据当成表数据一样,对undo数据的修改也会生成一些redo。
在进行实例恢复时,redo操作也会生成undo数据。
redo:恢复所有已提交的事务
2.实例失败(如主机掉电)可能出现的情况:
(1)已提交的事务只写到了online redo log,但没有写到数据文件中。(commit时,oracle先调用LGWR,再调用DBWR)
(2)没提交的数据写到了数据文件中。(内存不够用)
3.实例恢复的两个阶段
(1)rolling forward (Cache Recovery) :after rolling forward,the data files contain all committed changes recorded in the online redo log file.
These files could also contain uncommitted changes that were either saved to the data files before the failure.
(2)rolling back ( Transaction Recovery):any changes that were not committed must be undone.
4.redo 会把undo tabaleSpace或undo segment中的数据当成表数据一样,对undo数据的修改也会生成一些redo。
在进行实例恢复时,redo操作也会生成undo数据。
相关文章推荐
- 学习《Oracle 9i10g编程艺术》的笔记 (十二) redo 和undo 如何协作
- oracle REDO UNDO的区别
- Oracle基本数据改变原理浅析(redo与undo)--oracle核心技术读书笔记一
- ORACLE 临时表的REDO UNDO
- Oracle的redo 和undo的区别
- 【ORACLE】redo和undo_改变向量
- Oracle Undo & Redo
- Oracle中的Redo和Undo简单介绍
- 20151110 oracle事务 redo undo
- [Oracle] Redo&Undo梳理
- oracle redo and undo log
- ORACLE UNDO REDO查看
- Oracle redo undo commit rollback剖析
- Oracle的redo和undo的区别
- oracle redo undo
- 【转】ORACLE的REDO与UNDO
- Oracle Core 学习笔记一 -- Redo 和 Undo 机制详解
- Oracle的redo 和undo的区别
- Oracle的REDO和UNDO
- Oracle 9i & 10g编程艺术-深入数据库体系结构——第9章:redo与undo