一道题目不明白，请赐教!

恋家的老鼠

Which two operations require undo data?(Choose two)
A) commiting a transaction
B) rolling back a transaction
C) recovering from failed transactions
D) recording a transaction to redo log files
E) rolling forward during instance recovery

我觉得除了A、D明显不对以外剩下3答案都是对的，答案是BC。请教一下E为什么不对？

feiaix

没记错的话,roll forward用的是online log.而不是undo.

luffy.deng

rolling forward during instance recovery 用的是redo

nudtdk

原帖由 luffy.deng 于 2008-11-2 22:53 发表
rolling forward during instance recovery 用的是redo

正解

china_yebin

B和C
因为undo含有事务的数据，rollback的时候用到，事务恢复也会用到。

[ 本帖最后由 china_yebin 于 2008-11-7 15:52 编辑 ]

dzskyhgy

c和e

noamd_moon

如题所问， roll forward 需要的是redolog files ,放上一段 searchoracle.com 上关于roll forward 及roll back的对比描述，作者是: Kenny Smith


Roll forward refers to the process Oracle goes through to apply changes contained in the redo log files (both online and archive). The database clock (as measured by the system change number) is moved forward within the blocks of the datafile that are changed within the redo log vectors. Roll forward occurs during database, tablespace or datafile recovery and during crash recovery.

Rollback is the process of undoing uncommitted database transactions. The blocks copied to the rollback segments during transactions as a copy of the block for other transaction to read. When the instance aborts, the undo information in the redo log files must be applied to the database during the roll forward process of recovery. Therefore, during recovery, the database must roll forward and roll back.

雪凤凰

ora-600说过：
实例恢复的过程就是
前滚（redo）
打开
回滚（undo）