RAC SCAN Listener

SCAN (Single Client Access Name) is a new RAC 11gR2 feature so that the clients can connect Oracle databases in a cluster using a single name. The SCAN name must be resolvable without domain suffix to 3 IPs using a round-robin algorithm. The IP addresses must be on the same subnet as your public network in the cluster. Each time, the nslookup would return a set of 3 IPs in a different order. The client will try connecting one of the IPs received. If the client receives an error, it will try other IPs before returning an error. When a SCAN listener receives a connection request, it will redirect it to the local listener on the least loaded node. Finally the client establishes the connection to the database instance through the local listener on the node.

The REMOTE_LISTENER parameter should be set to the SCAN so that the instances can register to SCAN listeners to provide information about the current load, the recommendation on how many connections should be directed to the instance, and the services that are provided by the instance. The LOCAL_LISTENER parameter should be set to node-vip.

remote_listener -> scan-name.example.com:1521

local_listener -> (ADDRESS = (PROTOCOL=TCP) (HOST=node-vip.example.com) (PORT=1521))
service_names -> RACservice

Oracle 11gR2 client will use this TNS entry.

RACservice =
  (DESCRIPTION =
     (ADDRESS = (PROTOCOL = TCP) (HOST= scan-name.example.com) (PORT = 1521))
   (CONNECT_DATA = 
      (SERVER = DEDICATED)
      (SERVICE_NAME = RACservice)
   )
) 

To display configuration information for all SCAN listeners.

$ srvctl config scan_listener
To display configuration information for all SCAN VIPs.
$ srvctl config scan
To modify SCAN listener endpoints. Stop and Start SCAN listener and local listener on that node to take the new port.
$ srvctl modify scan_listener -p TCP:<new_port>
To Stop the SCAN listener.
$ srvctl stop scan_listener -i <ordinal_number>
To Start the SCAN listener.
$ srvctl start scan_listener -i <ordinal_number>
To display detailed configuration information for local listeners.
$ srvctl config listener -a
To modify port for local listener. Stop and start the local listener to take the new port.

$ srvctl modify listener -l listener -p TCP:<new_port>

To stop local listener

$ srvctl stop listener -n <node> -l listener

To start local listener.

$ srvctl start listener -n <node> -l listener

To remove local listener

$ srvctl remove listener -n <node> -l listener