377.AUM has been retaining about 15 minutes worth of undo. You want to double the retention period, but
not at the expense of new transactions failing. You decide to alter the system to set the parameter
UNDO_RETENTION=18000. However, AUM still retains only about 15 minutes worth of undo. What is the
problem? (Choose the best answer.)
A. You need to alter the undo tablespace to add the RETENTION GUARANTEE setting.
B. You need to increase the size of the undo tablespace.
C. The undo tablespace is not set to auto-extend.
D. You need to alter the Recycle Bin to add the RETENTION GUARANTEE setting.
Answer: C
答案解析：
题中说希望把保留时间变为30分钟，但是不能让新的事务失败为代价。
如果想把时间变为30分钟，有两个方法，一个是设置RETENTION GUARANTEE，确保保留时间为30分钟。
一个是让undo表空间自动增长。
而设置RETENTION GUARANTEE，但undo表空间是固定尺寸的情况下，会让新的事务失败。
故最好的办法就是让undo表空间自动增长。