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) ) )
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