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
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。