Oracle RAC服务器端的负载均衡是根据RAC中各节点的连接负荷数情况，将新的连接请求分配到负荷最小的节点上去。当数据库处于运行时，RAC中各节点的PMON进程每3秒会将各自节点的连接负荷数更新到service_register。而对于节点中任意监听器故障或监听器意外失败时，PMON进程会每1秒钟检查当前节点上的监听是否重启，以获得最新的负载信息来及时调整负载均衡。本文主要演示suse 10 + oracle 10g rac下的服务器端的负载均衡。

有关客户端的负载均衡可参考
      Oracle RAC 客户端连接负载均衡(Load Balance)
      配置RAC负载均衡与故障转移
 
有关Oracle 网络配置相关基础以及概念性的问题请参考：
        配置ORACLE 客户端连接到数据库
        配置非默认端口的动态服务注册
        配置sqlnet.ora限制IP访问Oracle
       Oracle 监听器日志配置与管理
       设置 Oracle 监听器密码(LISTENER)
       Oracle RAC 监听配置
       ORACLE RAC 下非缺省端口监听配置(listener.ora tnsnames.ora)

一、服务器端负载均衡配置

1、为tnsnames.ora 添加相应的网络服务名(每个节点配置)
  oracle@bo2dbp:~> more $ORACLE_HOME/network/admin/tnsnames.ora
  # tnsnames.ora Network Configuration File: /u01/oracle/db/network/admin/tnsnames.ora
  # Generated by Oracle configuration tools.
  
  remote_lsnr_gobo4 =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.7.61)(PORT = 1521))
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.7.62)(PORT = 1521))
    )
  
  local_lsnr_gobo4a =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.7.61)(PORT = 1521))
    )
  
  local_lsnr_gobo4b =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.7.62)(PORT = 1521))
    )
    
2、设置remote_listener参数
  alter system set remote_listener='<net_service_name>' scope=both sid='*';
  
  SQL> show parameter instance_name
  
  NAME                                 TYPE        VALUE
  ------------------------------------ ----------- ------------------------------
  instance_name                        string      GOBO4A
  SQL> show parameter listener
  
  NAME                                 TYPE        VALUE
  ------------------------------------ ----------- ------------------------------
  local_listener                       string
  remote_listener                      string
  
  SQL> alter system set remote_listener='remote_lsnr_gobo4' scope=both sid='*';
  
  System altered.

3、配置客户端tnsnames.ora
  -->客户端为suse 10
  SZDB:~ # ifconfig eth1 | grep "inet addr"|cut -d " " -f12|cut -d : -f2  #--客户端主机的ip
  192.168.7.2
  SZDB:~ # su - oracle
  oracle@SZDB:~> tail -10 $ORACLE_HOME/network/admin/tnsnames.ora
  GOBO4 =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.7.61)(PORT = 1521))
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.7.62)(PORT = 1521))
      (LOAD_BALANCE = off)   #--由于仅仅测试寄予服务器端的负载均衡，因此关闭客户端负载均衡选项
      (CONNECT_DATA =
        (SERVER = DEDICATED)
        (SERVICE_NAME = GOBO4)
      )
    )
  #Author : Robinson Cheng
  #Blog :   http://blog.csdn.net/robinson_0612  
 
4、检查监听情况
  oracle@bo2dbp:~> lsnrctl status
  Listening Endpoints Summary...
    (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.7.61)(PORT=1521)))
    (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.7.51)(PORT=1521)))
  Services Summary...
  Service "+ASM" has 1 instance(s).
    Instance "+ASM1", status BLOCKED, has 1 handler(s) for this service...
  Service "GOBO4" has 2 instance(s).
    Instance "GOBO4A", status READY, has 2 handler(s) for this service...
    Instance "GOBO4B", status READY, has 1 handler(s) for this service..
  .......
  
  oracle@bo2dbs:~> lsnrctl status
  Listening Endpoints Summary...
    (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.7.62)(PORT=1521)))
    (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.7.52)(PORT=1521)))
  Services Summary...
  Service &q