ORA-19816: WARNING: Files may exist in string that are not known to database.
Cause: One of the following events caused this:
1. A database crash happened during file creation.
2. A backup control file was restored.
3. The control file was re-created.
4. DB_RECOVERY_FILE_DEST has previously been enabled and then disabled.
Action: Use RMAN command CATALOG RECOVERY AREA to re-catalog any such files. If the file header is corrupted, then delete those files using an OS utility. Do not use messages 19817; it is used for simulating lock failure Do not use messages 19818; it is used for space reclamation before backup Do not use messages 19819; it is used to disable clearing file name
ORA-19816警告表明，当前字符串中可能存在一些数据库未知的文件，因此这可能会对某些操作产生影响。
ORA-19816警告：可能存在于字符串中而不被数据库识别的文件
1、检查字符串是否包含未知的文件，如果包含则必须修改字符串以移除文件；
2、将字符串中的文件改为标准格式，比如使用全路径来指定文件；
3、重新尝试原来的操作。