RMAN-08137 主库无法删除归档文件

crosscheck archivelog all;
delete noprompt force archivelog until time 'sysdate-6'; 
在主库删除归档时报如下错误
RMAN-08137: WARNING: archived log not deleted, needed for standby or upstream capture process

• 参考文档：RMAN-08137 on Primary Database although Archive Destination to Standby is deferred (文档 ID 1380368.1)

原因是log_archive_dest_state_x设置为DEFER，但是Oracle认为只要设置了log_archive_dest_n就会认为备库存在，只是暂时不可用而已，因此不会删除归档。
可以通过设置隐含参数（动态参数）来规避这个问题，默认值是true，该参数将认为延迟存档目的地完全不可用，并且不再为这些目的地保存归档日志

• 解决方法1:

alter system set "_deferred_log_dest_is_valid" = FALSE scope=both;

--修改前
NAME                                                         DESCRIPTION                                                            VALUE                                    ISDEFAULT  ISMODIFIED ISADJUSTED
------------------------------------------------------------ ---------------------------------------------------------------------- ---------------------------------------- ---------- ---------- ----------
_deferred_log_dest_is_valid                                  consider deferred log dest as valid for log deletion (TRUE/FALSE)      TRUE                                     TRUE       false      false

--修改后
NAME                                                         DESCRIPTION                                                            VALUE                                    ISDEFAULT  ISMODIFIED ISADJUSTED
------------------------------------------------------------ ---------------------------------------------------------------------- ---------------------------------------- ---------- ---------- ----------
_deferred_log_dest_is_valid                                  consider deferred log dest as valid for log deletion (TRUE/FALSE)      FALSE                                    TRUE       system_mod false

• 解决方法2

delete noprompt force archivelog all completed before 'sysdate-6';