搭建DG最后一步打开时报错如下：
SQL> alter database open read only;
alter database open read only
*
ERROR at line 1:
ORA-10458: standby database requires recovery
ORA-01152: file 1 was not restored from a sufficiently old backup
ORA-01110: data file 1: '/data/oradata/orcl/system01.dbf'
ORA-16043: Redo apply has been canceled.
ORA-16016: archived log for thread 1 sequence# 61 unavailable
ORA-10877: error signaled in parallel recovery slave
ORA-10877: error signaled in parallel recovery slave
ORA-10877: error signaled in parallel recovery slave
错误原因：少归档。
解决办法：从主库传送归档到备库恢复即可，命令如下：
先 recover managed standby database cancel;
再执行：
RMAN> recover database;