文档解释
ORA-19693: backup piece string already included
Cause: This backup piece was already specified for inclusion in the restore conversation. A restore conversation may process only a single instance of a backup piece.
Action: Remove the specified duplicate backup piece in restore steps and restart the conversation.
ORA-19693表示指定的备份块字符串已经被包含，oracle数据库无法继续备份。
官方解释
ORA-19693: backup piece string already included
Cause: An attempt was made to back up a piece that was already backed up. There may be other causes, including user errors.
Action: Investigate the cause of the error and take appropriate action.
常见案例
当在使用RMAN备份命令备份数据库的过程中，添加了块字符串（block_list），且其中指定的块字符串（block_list）已经包含在备份文件中，会触发ORA-19693错误。
一般处理方法及步骤
1、检查添加的block_list是否包含已经被备份了的字符串，如果是，移除该字符串；
2、故障检查完成后，重新运行备份指令即可。
