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Your database is running under automatic undo management and the UNDO_RETENTION parameter is set to 900 sec. You executed the following command to enable retention guarantee： SQL> ALTER TABLESPACE undotbs1 RETENTION GUARANTEE； What effect would this statement have on the database？（）
A:The extents in undo tablespace retain data until the next full database backup.
B:The extents containing committed data in the undo tablespace are never overwritten.
C:The extents which no longer contain uncommitted data in the undo tablespace are not overwritten for at least15 minutes.
D:The extents containing committed data in the undo tablespace are not overwritten until the instance is shut down.

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出自：Oracle认证

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