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Re: 关于回滚未提交的事务的疑问?
最初由 fragrant 发布
[B]oracle的ppt中有这样一句:
State of the data before COMMIT or ROLLBACK statements are issued:
其中之一就是ata manipulation operations primarily affect the database buffer也就是在事务未提交之前,数据改变仅仅是在buffer里.
那么为什么在数据库恢复重启的时候,需要回滚未提交的事务呢?
我刚学,很多问题想不明白,望各位点拨! [/B]
1) commit: guarantee data has been written
into redo log ( not datafile)
2) dirty buffer written to datafile must happen
after it goes to redo log, and it could happen
after or before commit.
3) rollback segment is for before-image of
a block, for rollback or consistent data image
of other statement |
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