SCAN(Single Client Access Name)是Oracle从11g R2开始引入的，客户端可以通过SCAN特性负载均衡地连接到RAC群集。SCAN是一个域名，可以解析至少1个IP，至多3个IP，SCAN IP需要与public IP在一个子网内。SCAN域名可以通过DNS或GNS的方式来解析，GNS是11GR2引入的，可以通过DHCP服务为节点和SCAN分配VIP和SCAN IP，当然也可以采用HOST解析的方式来配置SCAN，这种方式就只能定义一个SCAN IP。
在引入SCAN之前，客户端连接RAC群集需要配置所有节点的监听信息以及FAILOVER配置，如下列配置
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| ORCL = (DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.0.139.161)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.0.139.162)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = orcl)
(FAILOVER_MODE =
(TYPE = select)
(METHOD = basic)
(RETRIES = 180)
(DELAY = 5)
)
)
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在配置SCAN后，客户端仅需要连接SCAN LISTENER，由SCAN来完成FAILOVER，负载均衡等内容
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| ORCL =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.0.139.163)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = orcl)
)
)
|