同一个主机的同一个数据库，只能有一个监听器，我们所配置多个监听器时，它会监听另外一台主机上的数据库，但这样性能不好。
listener.ora配置文件讲解：
监听器部分：
LISTENER =
 (DESCRIPTION_LIST =
   (DESCRIPTION =
    (ADDRESS=(PROTOCOL = IPC) (KEY=EXTPRO1))
    (ADDRESS=(PROTOCOL = TCP)(HOST = 192.168.2.29)(PORT = 1521))   
    )
 )
数据库配置部分：
SID_LIST_LISTENER =
 (SID_LIST =
  (SID_DESC =
   (GLOBAL_DBNAME = orcl.localdomain)
   (ORACLE_HOME = /opt/oracle/product/11.2.0/dbhome_1)
   (SID_NAME = orcl )   
  )
  )

tnsname.ora配置文件

test =
 (DESCRIPTION =
 (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.29)(PORT = 1521))
 (CONNECT_DATA =
   (SERVICE_NAME = orcl.localdomain)
 )


service_name 默认就是global_name.
查询global_name
select  *  from  global_name;
修改global_name
alter database rename global_name to orcl;
update global_name  set global_name = 'orcl';
commit;
但是修改了、global_name并不会默认改掉server_name,也不会默认修改db_domain;
因此修改db_domain
alter  system set db_domain='' scope=spfile;