在oracle 10g 中，传输日志到备用节点数据库的进程为arch 和lgwr 。（在11g 中，lgwr 被lns 替代，但10g 中是不是lgwr 我不确定！
1.    架构
在oracle 10g 中，传输日志到备用节点数据库的进程为arch 和lgwr 。（在11g 中，lgwr 被lns 替代，但10g 中是不是lgwr 我不确定！）
在备用节点上通过参数log_archive_config 、fal_client 和fal_server 接收日志，并和主节点通讯，，标识该日志是否被应用。
data guard 采用最大可用模式，保证数据实时同步到最少一个节点上。因为我们选择第一个备用节点作为数据实时同步点，同步进程采用lgwr 进程。
2.    配置
在一个主节点两个备用节点的data guard 10g 的环境中，各个节点的初始化参数的主要配置项。
在主节点的初始化参数文件配置：
*.log_archive_config='dg_config=(codb,codg,codg2)'
*.log_archive_dest_1='location=/oradata/htcodb/archive_logs_codb'
*.log_archive_dest_2='service=codb_standby lgwr sync affirm  valid_for=(online_logfiles,primary_role) db_unique_name=codg'
*.log_archive_dest_3='service=codb_standby2 arch async affirm  valid_for=(online_logfiles,primary_role) db_unique_name=codg2'
*.log_archive_dest_state_2='enable'
*.log_archive_dest_state_3='enable'
在备用节点一的初始化参数文件配置：
*.db_name='codb'
*.db_unique_name='codg'
*.fal_client='code_standby'
*.fal_server='codb_primary'
*.log_archive_config='dg_config=(codb,codg,codg2)'
*.log_archive_dest_1='location=/oradata/archivelog/ valid_for=(all_logfiles,all_roles) db_unique_name=codg'
*.log_archive_format='%t_%s_%r.dbf'
在备用节点二的初始化参数文件配置：
*.db_name='codb'
*.db_unique_name='codg2'
*.fal_client='codb_standby'
*.fal_server='codb_primary'
*.log_archive_config='dg_config=(codb,codg2)'
*.log_archive_dest_1='location=/u01/archivelog_standby/ valid_for=(all_logfiles,all_roles) db_unique_name=codg2'
*.log_archive_format='%t_%s_%r.dbf'
主节点和备用节点之间的通讯是通过oracle net 实现的。在参数fal_client 和fal_server 上就用到oracle net 中的配置信息。
在主节点的tnsnames.ora 文件中，关于dg 的配置项如下所示：
codb_primary =
 (description =
   ( address = (protocol = tcp)(host = codb1-vip.htsc.com.cn)(port = 1521))
  (address = (protocol = tcp)(host = codb2-vip.htsc.com.cn)(port = 1521))
  (load_balance = yes)
  (connect_data =
    (server = dedicated)
    (service_name = codb)
  )
 )-
codb_standby =
 (description =
  (address_list =
    (address = (protocol = tcp)(host = 192.168.15.219)(port = 1521))
  )
  (connect_data =
    (sid = codb)
  )
 )
codb_standby2 =
 (description =
  (address_list =
    (address = (protocol = tcp)(host = 192.168.15.90)(port = 1521))
  )
  (connect_data =
    (sid = codb)
  )
 )
在备用节点一的tnsnames.ora 文件中，关于dg 的配置项如下所示：
codb_primary =
 (description =
  (address = (protocol = tcp)(host = codb1-vip.htsc.com.cn)(port = 1521))
  (address = (protocol = tcp)(host = codb2-vip.htsc.com.cn)(port = 1521))
  (load_balance = yes)
  (connect_data =
    (server = dedicated)
    (service_name = codb)
  )
 )
codb_standby =
 (description =
  (address_list =
    (address = (protocol = tcp)(host = 192.168.15.219)(port = 1521))
  )
  (connect_data =
    (service_name = codb)
  )
 )
在备用节点二的tnsnames.ora 文件中，关于dg 的配置项如下所示：
codb_primary =
 (description =
  (address = (protocol = tcp)(host = codb1-vip.htsc.com.cn)(port = 1521))
  (address = (protocol = tcp)(host = codb2-vip.htsc.com.cn)(port = 1521))
  (load_balance = yes)
  (connect_data =
    (server = dedicated)
    (service_name = codb)
  )
 )
codb_standby =
 (description =
  (address_list =
    (address = (protocol = tcp)(host = 192.168.15.90)(port = 1521))
  )
  (connect_data =
    (service_name = codb)
  )
 )