OCP考试052考题：1Z0-V8.02-第29题
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29. Your database instance is configured with automatic undo management and the UNDO_RETENTION
parameter is set to 900 seconds. You executed the following command to enable retention guarantee:
SQL> ALTER TABLESPACE undotbs1 RETENTION GUARANTEE;
What effect would this command have on the database?
A.The extents in the undo tablespace retain data until the next full database backup.
B.The extents containing committed undo in the undo tablespace are not overwritten for at least 15
minutes.
C.The extents containing committed data in the undo tablespace are not overwritten until the instance is
shut down.
D.The extents containing committed undo in the undo tablespace are transferred to Flash Recovery Area
before being overwritten.
Answer: B
答案解析：
默认还原行为是覆盖已提交、但尚未过期的事务处理的还原信息，而不是让活动事务处理因缺少还原空间而失败。
保证保留时间会改变此行为。有了保留时间保证，即使会导致事务处理失败，仍然会强制执行还原保留时间设置。
