248.You want the ability to recovery any time within the last seven days and therefore you configured the
recovery window retention policy using the command:
RMAN> CONFIGURE RETENTION POLICY TO RECOVFRY WINDOW OF 7 DAYS;
After configuring the recovery window, you performed the database backup as follows:
A. Backup RB1 at log sequence number 12871 on 5th Jan
B. Backup RB2 at log sequence number 15622 on 12th Jan
C. Backup RB3 at log sequence 16721 on 15th Jan
D. On 20th Jan when the log sequence number was 18112 you realize that there Is a need to a point in time at the beginning of the recovery window. You have all an hived redo log files to date.
Answer: D
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmconfb.htm#BRADV89437
这道题的答案没理解到什么，不过知道CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 7 DAYS;是什么意思就可以了。
Configuring a Recovery Window-Based Retention Policy
The RECOVERY WINDOW parameter of the CONFIGURE command
specifies the number of days between the current time and the earliest point of recoverability. RMAN does not consider any full or level
0 incremental backup as obsolete if it falls within the recovery window. Additionally, RMAN retains all archived logs and level 1 incremental backups that are needed to recover to a random point within the window.
Run the CONFIGURE RETENTION POLICY command at the RMAN prompt. This example ensures that you can recover the database to any point within the last week:
RMAN does not automatically delete backups rendered obsolete by the recovery window. Instead, RMAN shows them as OBSOLETE in the REPORT OBSOLETE output and in the OBSOLETE column of V$BACKUP_FILES.
RMAN deletes obsolete files if you run the DELETE OBSOLETE command.