USING CURRENT LOGFILE optioin of RECOVERED MANAGED STANDBY DATABASE statement
#等主库switch log 的时候 才传输归档日志到备库
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
 
#实时把主库的日志传输到备库,但在执行这条语句之前要 配置好 standby logfile
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION;

Reference:
http://www.itpub.net/thread-1625382-1-1.html