以oracle net看，数据库服务器可能也是客户端，因为tnsnames.ora可以有服务器的描述。也就是，只有监听器才会一直是服务器
以oracle net看，数据库服务器可能也是客户端，因为tnsnames.ora可以有服务器的描述。也就是，只有监听器才会一直是服务器
实例：监听=n：m
㈠ 双监听器的好处：
① 客户端故障转移--cf
② 客户端负载均衡--clb
㈡ 注意事项：
① 要保证1521端口可用，否则，，oem将不可用，须emca重配
② 非标端口使用静态注册是个比较好的实践
配置案例：
[oracle@localhost admin]$ cat listener.ora 
think = 
  (description = 
    (load_balance = on) 
    (failover = on) 
    (address_list = 
      (address=(protocol = tcp)(host= 192.168.1.113)(port= 1521) 
      (address=(protocol = tcp)(host= 192.168.1.113)(port= 1522) 
    ) 
    ) 
  )
sid_list_think = 
  (sid_list = 
    (sid_desc = 
      (global_dbname = emrep.us.oracle.com) 
      (sid_name = emrep) 
      (oracle_home = /u01/app/oracle/product/10.2.0/db_1)))
water = 
  (description = 
    (load_balance = on) 
    (failover = on) 
    (address_list = 
      (address=(protocol = tcp)(host= 192.168.1.113)(port= 1521)) 
      (address=(protocol = tcp)(host= 192.168.1.113)(port= 1522)) 
    ) 
    ) 
  )
sid_list_water = 
  (sid_list = 
    (sid_desc = 
      (global_dbname = emrep.us.oracle.com) 
      (sid_name = emrep) 
      (oracle_home = /u01/app/oracle/product/10.2.0/db_1)))
[oracle@localhost admin]$ lsnrctl status water
lsnrctl for linux: version 10.2.0.1.0 - production on 10-dec-2012 21:47:22
copyright (c) 1991, 2005, oracle.  all rights reserved.
connecting to (description=(load_balance=on)(failover=on)(address=(protocol=tcp)(host=192.168.1.113)(port=1521))) 
status of the listener 
------------------------ 
alias                    listener 
version                  tnslsnr for linux: version 10.2.0.1.0 - production 
start date                10-dec-2012 20:02:23 
uptime                    0 days 1 hr. 44 min. 58 sec 
trace level              off 
security                  on: local os authentication 
snmp                      off 
listener parameter file  /u01/app/oracle/product/10.2.0/db_1/network/admin/listener.ora 
listener log file        /u01/app/oracle/product/10.2.0/db_1/network/log/listener.log 
listening endpoints summary... 
  (description=(address=(protocol=tcp)(host=localhost.localdomain)(port=1521))) 
services summary... 
service emrep.us.oracle.com has 1 instance(s). 
  instance emrep, status ready, has 1 handler(s) for this service... 
service emrep_xpt.us.oracle.com has 1 instance(s). 
  instance emrep, status ready, has 1 handler(s) for this service... 
the command completed successfully
如果1521和1522并存，在业务不繁忙时，listener进程只会使用1521
[oracle@localhost admin]$ lsnrctl status water
lsnrctl for linux: version 10.2.0.1.0 - production on 10-dec-2012 21:48:45
copyright (c) 1991, 2005, oracle.  all rights reserved.
connecting to (description=(load_balance=on)(failover=on)(address=(protocol=tcp)(host=192.168.1.113)(port=1522))) 
status of the listener 
------------------------ 
alias                    water 
version                  tnslsnr for linux: version 10.2.0.1.0 - production 
start date                10-dec-2012 21:24:17 
uptime                    0 days 0 hr. 24 min. 28 sec 
trace level              off 
security                  on: local os authentication 
snmp                      off 
listener parameter file  /u01/app/oracle/product/10.2.0/db_1/network/admin/listener.ora 
listener log file        /u01/app/oracle/product/10.2.0/db_1/network/log/water.log 
listening endpoints summary... 
  (description=(address=(protocol=tcp)(host=192.168.1.113)(port=1522))) 
services summary... 
service emrep.us.oracle.com has 1 instance(s). 
  instance emrep, status unknown, has 1 handler(s) for this service... 
the command completed successfully