在一次搭建oracle 10G dataguard时，主库无法传日志到备库，alert日志报如下错误：
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor
PING[ARC0]: Heartbeat failed to connect to standby 'TEST3_DG'. Error is 12514.
tinsping TEST3_DG 是通的，比较有用的诊断方法是，在主库执行命令：
sqlplus sys/password@TEST3_DG as sysdba
还是报如下错误：
ERROR:
ORA-12514: TNS:listener does not currently know of service requested in connect
descriptor
说明备库的监听配置有问题，仔细检查了listener.ora,确实是发现了错误，修正之后同步正常。
