31. Which statement is true about the UNDO_RETENTION parameter when retention guarantee is not
enabled?
A.It is the time period after which the undo data becomes obsolete.
B.It is the time period after which the committed undo data would be transferred to a temporary
tablespace.
C.It is the minimum time period up to which the committed undo data would be retained if free undo space
is available.
D.It is the time period after which the undo data is transferred to the Flash Recovery Area to provide read
consistency.
Answer: C
答案解析：
此题考意，当 retention guarantee 没有设置时，UNDO_RETENTION 的情况。
当 retention guarantee 没有设置时，即undo数据 不强制保留UNDO_RETENTION 所设置的时间内，如果是undo表空间是自动增长，即在足够的空闲空间下，则可能会保留到UNDO_RETENTION 所设置的时间。如果undo表空间是固定的，则UNDO_RETENTION 可能会被忽略，undo数据可能被覆盖。
C答案：如果有足够的空闲undo表空间，则undo数据会保留，保留的时间为UNDO_RETENTION所设置的时间。是正确的。