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The feature of SCAN (Single Client Access Name) is introduced in Oracle 11g R2. The advantage of this feature is that a virtual service layer is added between the database and the client, that is, the so-called SCAN IP and SCAN IP Listener. The client only needs to configure the tns information of SCAN IP and connect to the background cluster database through SCAN IP Listener. In this way, no matter whether the cluster database has the operation of adding or deleting nodes, it will not affect the Client.

The process for the client to connect to the database instance through scan IP is: client-> scan listener-> local listener-> local instance

There are two ways to use scan:

1. Define the domain name in DNS.

2. Implement DHCP customization through Grid Naming Server (GNS) provided by Oracle.

If you do not want to use the above two methods, you can modify the hosts file of the two servers to add scan-cluster.localdomain 172.16.0.75. This method is not recommended by oracle because it can only define one SCAN IP.

Load balancing:

On the server side, remote_listener is set to SCAN Listener by default

On the client side, the configuration of tnsnames.ora is as follows:

RAC =

(DESCRIPTION =

(ADDRESS = (PROTOCOL = TCP) (HOST = scan-cluster.localdomain) (PORT = 1521))

(CONNECT_DATA =

(SERVER = DEDICATED)

(SERVICE_NAME = rac)

))

How the client connects

$sqlplsu / @ RAC

The connection to EZconnet still applies to SCAN

$sqlplus / @ scan-cluster.localdomain:1521/rac

Check the cluster load: > select inst_id,count (*) from gv$session group by inst_id

Check which node the user is on > select instance_name from v$instance

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