run{CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 8 DAYS;delete noprompt obsolete device type disk;} 执行之后无报错！ 但是未删除任何信息？？？ 是不是21天前的备份信息，根本不在控制文件中？？？ 使用catalog 注册一下备份片信息 catalog start with '/bak'; yes --发现n多备份信息，可以被注册，说明什么，说明21天前的很多备份信息，确实在控制文件中不存在了？？？

控制文件默认保留时间7天，也就是说，当控制文件积累到一定大小的程度时，会自动清理备份记录信息（不会删除备份文件，只是删除控制文件中记录的备份信息） 以及归档信息 SQL> show parameter control_file_record_keep_timeNAME                                 TYPE                   VALUE------------------------------------ ---------------------- ------------------------------control_file_record_keep_time        integer                7

    Relation between RMAN retention period and control_file_record_keep_time (Doc ID 397269.1)

    RMAN backup keeps the backup metadata information in the reusable section of the controlfile. It depends on the parameter CONTROL_FILE_RECORD_KEEP_TIME. CONTROL_FILE_RECORD_KEEP_TIME specifies the minimum number of days before a reusable recordin the control file can be reused. In the event a new record needs to be added to a reusable section and there is not enough space then it will delete the oldest record, which are aged enough. 

    Backup retention policy is the rule to set regarding which backups must be retained (whether on disk or other backup media) to meet the recovery and other requirements.

If the CONTROL_FILE_RECORD_KEEP_TIME is less than the retention policy then it may overwrite reusable records prior to obsoleting them in the RMAN metadata. Therefor it is recommended that the CONTROL_FILE_RECORD_KEEP_TIME should set to a higher value than the retention policy.     Please note the default control_file_record_keep_time is 7 dayNOTE: Best practice is to NOT set control_file_record_keep_time to a value greater than 10. If you need retention greater than this in the controlfile, you should use an RMAN catalog.    Formula     CONTROL_FILE_RECORD_KEEP_TIME = retention period + level 0 backup interval + 1    For e.g.     e.q. level 0 backup once a week with retention policy of a recovery windows of 14 days then in this case the CONTROL_FILE_RECORD_KEEP_TIME should be 14+7+1=22    To be on safer side you can always add + 2 or 3 days to above formula.Ideally its recommended to configure a recovery catalog so that information about the backups are present in recovery catalog even though the controlfile section gets reused based on the control_file_record_keep_time due to space pressure.

SQL> select * from V$CONTROLFILE_RECORD_SECTION; 有人会问？  为什么超出默认的7天？ 但是备份信息还是保留呢？  空间足够没必要覆盖，备份信息过多才会自动清理。 那么如何处理？？？  1.不建议直接跳转加大参数，无法调整清理备份信息在进行调整； SQL> alter system set control_file_record_keep_time=31 sid='*';                  2.备份的定时任务是否有必要进行调整，及时清理多余的备份信息；                  3.可以脚本中加上RMAN> catalog start with '/bak/' noprompt;

searching for all files that match the pattern /bak/

List of Files Unknown to the Database

=====================================File Name: /bak/0buvkgthFile Name: /bak/0cuvkgtkcataloging files...cataloging done

List of Cataloged Files

=======================File Name: /bak/0buvkgthFile Name: /bak/0cuvkgtk

 

使用catalog 注册后，再次执行删除语法，可以执行，但是执行删除8天前的日志，但是却保留了2周的备份信息！！！

每周一次备份