问题描述：用备份进行DG恢复，恢复过程中报错ORA-19870: error while restoring backup piece /backup/db_BJCCORA_20180724_02t8qbe6_1_1
ORA-19870: error while restoring backup piece /backup/db_BJCCORA_20180724_02t8qbe6_1_1
ORA-19505: failed to identify file "/backup/db_BJCCORA_20180724_02t8qbe6_1_1"
ORA-27037: unable to obtain file status
Linux-x86_64 Error: 2: No such file or directory
Additional information: 3
生成的是备库控制文件，但是恢复过程却是像恢复一个库一样。最后想起来这个备库的控制文件生成是在数据库全备之前生成的。导致控制文件找不到备份，
重新生成一个备库控制文件，恢复成功
alter database create standby controlfile as '/tmp/bjccorastb1.ctl';
