AUM (Automatic UNDO Management) 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.
C is correct:
https://docs.oracle.com/cd/B19306_01/server.102/b14231/undo.htm
The following points explain the exact impact of the UNDO_RETENTION parameter on undo retention:
The UNDO_RETENTION parameter is ignored for a fixed size undo tablespace. The database may overwrite unexpired undo information when tablespace space becomes low.
For an undo tablespace with the AUTOEXTEND option enabled, the database attempts to honor the minimum retention period specified by UNDO_RETENTION. When space is low, instead of overwriting unexpired undo information, the tablespace auto-extends. If the MAXSIZE clause is specified for an auto-extending undo tablespace, when the maximum size is reached, the database may begin to overwrite unexpired undo information.