Oracle 11gR2 RAC中引入了SCAN的概念。SCAN全稱是Single Client Access Name ，它是Oracle RAC 11gR2版本的一個新特性。它為需要訪問Oracle集群數據的客戶端提供一個簡單名字。它的好處是如果你使用SCAN當你增長或踢除集群中的節點時客戶端不需要做任何改變，這一點在三層架構套用系統中（資料庫-套用伺服器-客戶機）優勢明顯。使用單個名字去訪問集群允計客戶端使用EZConnect 客戶端和簡單JDBC thin URL去訪問運行在集群中的任何資料庫，而不用管在集群中那個或那些伺服器（或叫實例）是Active的。
SCAN provides load balancing and failover of client connections to the database. The SCAN works as an IP alias for the cluster.Oracle strongly recommends that you do not configure SCAN VIP addresses in the hosts file. Use DNS resolution for SCAN VIPs. If you use the hosts file to resolve SCANs, then you will only be able to resolve to one IP address and you will have only one SCAN address.
