oracle tnsnames.ora配置

本地命名参数，存放位置一般在：$ORACLE_HOME/network/admin目录下
tnsnames.ora主要是做名称映射的。连接描述字符串中服务与本地命名方法的映射（客户端）；网络请求中的服务名与本地监听的地址映射（服务端）。

tnsnames.ora的基本语法
DESCRIPTION包含整个连接描述，ADDRESS包含协议地址，CONNECT_DATA包含数据库服务ID信息

标准格式：
net_service_name=
(DESCRIPTION=
(ADDRESS=(protocol_address_information))
(CONNECT_DATA=
(SERVICE_NAME=service_name)))

多重描述
一个网络服务名可以对应多个DESCRIPTION，一个DISCRIPTION可包含多个地址
标准格式：
net_service_name=
(DESCRIPTION_LIST=
(DESCRIPTION=
(ADDRESS=(protocol_address_information))
(ADDRESS=(protocol_address_information))
(ADDRESS=(protocol_address_information))
(CONNECT_DATA=
(SERVICE_NAME=service_name)))
(DESCRIPTION=
(ADDRESS=(protocol_address_information))
(ADDRESS=(protocol_address_information))
(ADDRESS=(protocol_address_information))
(CONNECT_DATA=
(SERVICE_NAME=service_name))))

客户端负载均衡与容灾
sample=
(DESCRIPTION=
(LOAD_BALANCE=on)
(FAILOVER=on)
(ADDRESS_LIST=
(SOURCE_ROUTE=yes)
(ADDRESS=(PROTOCOL=tcp)(HOST=host1)(PORT=1630))
(ADDRESS=(PROTOCOL=tcp)(HOST=host2)(PORT=1521)))
(ADDRESS_LIST=
(SOURCE_ROUTE=yes)
(ADDRESS=(PROTOCOL=tcp)(HOST=host3)(port=1630))
(ADDRESS=(PROTOCOL=tcp)(HOST=host4)(port=1521)))
(CONNECT_DATA=(SERVICE_NAME=sales.us.acme.com)))

额外参数配置：
FAILOVER
LOAD_BALANCE
RECV_BUF_SIZE
SDU
SEND_BUF_SIZE
SOURCE_ROUTE
TYPE_OF_SERVICE（如rdb）