service_names配置不正确，导致dg创建失败
伙伴发来消息，创建dg后，主备一直无法进行日志同步。
以下是查看过程
备库的alert日志：
2018-11-13T17:47:36.231294+08:00Errors in file /d12/app/oracle/diag/rdbms/orcls/test/trace/test_m000_20088.trc:ORA-01110: data file 1: '/u01/app/oracle/oradata/orcl/system01.dbf'2018-11-13T17:47:36.311896+08:00Errors in file /u01/app/oracle/diag/rdbms/orcls/test/trace/test_m000_20088.trc:ORA-01110: data file 3: '/u01/app/oracle/oradata/orcl/sysaux01.dbf'2018-11-13T17:47:36.394797+08:00Errors in file /u01/app/oracle/diag/rdbms/orcls/test/trace/test_m000_20088.trc:ORA-01110: data file 4: '/u01/app/oracle/oradata/orcl/undotbs01.dbf'2018-11-13T17:47:36.480646+08:00Errors in file /u01/app/oracle/diag/rdbms/orcls/test/trace/test_m000_20088.trc:ORA-01110: data file 7: '/u01/app/oracle/oradata/orcl/users01.dbf'2018-11-13T17:47:40.958801+08:00 Started logmerger process2018-11-13T17:47:40.979088+08:00Managed Standby Recovery starting Real Time Apply2018-11-13T17:47:41.067310+08:00Parallel Media Recovery started with 4 slaves2018-11-13T17:47:41.140323+08:00Media Recovery Waiting for thread 1 sequence 49Fetching gap sequence in thread 1, gap sequence 49-492018-11-13T17:47:41.938608+08:00Completed: alter database recover managed standby database disconnect from session
可以看到在执行alter database recover managed standby database disconnect from session后，备库就一致hang在那里了。
standby库查看：
SQL> select client_process, process, thread#, sequence#, status from v$managed_standby where client_process='LGWR' or process='MRP0';CLIENT_P PROCESS THREAD# SEQUENCE# STATUS-------- --------- ---------- ---------- ------------N/A MRP0 1 49 WAIT_FOR_GAPSQL>
也可以看出，日志没有进行传输。
然后在primary库查看：
SQL> select error from v$archive_dest;ERROR-----------------------------------------------------------------ORA-12514: TNS:listener does not currently know of servicerequested in connect descriptor
查看显示tns有问题！
就让其测试tnsping的结果。结果显示都是通的。继续查看主备的tnsnames.ora文件(二者配置相同)：
$ more tnsnames.ora#primaryORCL = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.20.10)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orcl) ) )#standbyORCLS = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.20.11)(PORT = 1521)) ) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orcl) ) )
可以看到primary库的service_name是orcl，standby库的service_name也是orcl。
这里就有问题了。因为默认service_names=DB_UNIQUE_NAME.DB_DOMAIN。一般在测试的时候是不设置db_domain的值的，service_names值就设置成了DB_UNIQUE_NAME。但是primary和standby是不可以具有相同的DB_UNIQUE_NAME的，因此这里standby的service_name就有问题了。
因此，需要修改primary和standby端的tnsnames.ora文件。