（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.

答案：（B）

解析：

A（X）. 设置undo保留期与备份没有任何关系

C（X）. 被提交的事务的undo数据，是有可能被覆盖的（这取决于数据文件是否是自动增长，及是否设置了保留期保证）

D（X）. 不存在

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Oracle 11G OCP 1Z0-052 29