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最新推荐文章于 2025-12-15 21:10:21 发布

转载最新推荐文章于 2025-12-15 21:10:21 发布 · 70 阅读

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原文链接：http://www.cnblogs.com/Babylon/p/8623953.html

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#数据库

本文探讨了Oracle数据库中如何处理异常终止的用户会话，特别是在事务中途终止的情况下。Oracle使用撤销数据进行事务回滚，确保数据库一致性。此外，文章还深入介绍了撤销记录的作用，包括事务回滚、数据库恢复、提供读一致性以及使用Oracle闪回特性进行逻辑错误恢复。

One of the user sessions was terminated abnormally in the middle of a transaction.

What does Oracle database do to recover it?

A. uses undo data for roll forward

B. uses Flashback Log for recovery

C. uses online redo logs to roll back

D. uses undo data to roll back the transaction

E. uses Recovery Manager (RMAN) to roll back

F. uses the System Monitor (SMON) background process to perform instance recovery

Answer: D

What Is Undo?

Oracle Database creates and manages information that is used to roll back, or undo, changes to the database. Such information consists of records of the actions of transactions, primarily before they are committed. These records are collectively referred to as undo.

Undo records are used to:

Roll back transactions when a ROLLBACK statement is issued
Recover the database
Provide read consistency
Analyze data as of an earlier point in time by using Oracle Flashback Query
Recover from logical corruptions using Oracle Flashback features

When a ROLLBACK statement is issued, undo records are used to undo changes that were made to the database by the uncommitted transaction. During database recovery, undo records are used to undo any uncommitted changes applied from the redo log to the data files. Undo records provide read consistency by maintaining the before image of the data for users who are accessing the data at the same time that another user is changing it.

转载于:https://www.cnblogs.com/Babylon/p/8623953.html