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

自动撤消管理(AUM(Automatic UNDO Management))已保留约15分钟的撤消值。你想对保留期限加倍，但不能以新事务的失败为代价。您决定改变系统设置参数撤消保留=1800（30分钟）。然而，自动撤消管理仍保留大约只有15分钟的撤消值。问题是什么？

C、撤销表空间没有设置为自动扩展。正确。

AUM will ignore the UNDO_RETENTION parameter if the undo tablespace is not set to autoextend. Option A is incorrect because guaranteeing retention could result in failed transactions, which you are specifically wanting to avoid. Option B is not the best answer because the size of the undo tablespace is not the cause of the issue, but increasing the size of the undo tablespace could increase the amount of undo retained. Option D is wrong because this question is not dealing with the Recycle Bin and because it has no guaranteed retention setting.
自动撤消管理将忽略UNDO_RETENTION参数，如果撤销表空间没有设置为自动扩展。
选项A是不正确的，因为保留保证可能导致失败的交易，而这是你专门想避免的。
选项B不是最好的答案，因为撤销表空间的大小不是问题的原因，但增加撤销表空间的大小可以增加撤消保留量。
选项D是错误的，因为这个问题不处理回收站且因为它没有保证保留设置。