About Oracle 11gR2 Grid Infrastructure Single Client Access

About Oracle 11gR2 Grid Infrastructure Single Client Access Name (SCAN) Oracle11gR2Grid Infrastructure (CRS) introduces Single Client Access Name (SCAN) to simplify Client Access to database services, this article describes in detail the meaning and working principle of SCAN. SCAN concept Single client access name (SCAN) is the virtual host name provided to all clients for connecting to the cluster (corresponding to the vip host name in 10g and 11g R1 ). SCAN is a domain name registered with 1-3 IP addresses in DNS or Grid Naming Service (GNS. By default, the SCAN name is the same as the cluster name and must be unique within the same enterprise. The default value of SCAN is based on the name of the local node. The SCAN name must contain at least 1 character and a maximum of 15 characters. It must contain letters and numbers. It cannot start with a number or contain hyphens (-). If you want to use a SCAN with a length of more than 15 characters, select the "Advanced installation" option when installing Grid Infrastructure. To successfully install Grid Infrasture, SCAN must be resolved to at least one IP address. The scan vip address must be in the same subnet as the virtual IP address and public IP address. We strongly recommend that you do not configure the scan vip address in the hosts file. If you use the hosts file to parse the SCAN host name, the SCAN hostname can only be parsed into one scan ip address. If you use the hosts file to parse the SCAN host name, a Cluster Verification Utility fault similar to the following will occur at the end of Grid Infrastructure installation. Installation log-$ ORACLE_BASE/oraInventory/logs/installActions {$ TIMESTAMP }. logINFO: PRVG-1101: SCANname "cluscan.us.oracle.com" failed to resolveINFO: ERROR: INFO: PRVF-4664: Found inconsistent name resolution entries for SCAN name "cluscan.us.oracle.com" INFO: ERROR: INFO: PRVF-4657: name resolution setup check for "scanclunm" (IP address: 10.4.0.202) failedORPRCS-1016: Failed to resolve Single Client Access Namecluscan.us.oracle.com for high availability and scalability, Oracle recommends that you use DNS loop resolution to resolve SCAN to three addresses. Because SCAN is associated with the entire cluster rather than a specific node, you can use SCAN to easily add or delete nodes from the cluster without re-configuring the client. SCAN also enhances database location independence so that the client configuration department is dependent on nodes running specific databases. The client can still access the cluster using the method of the previous version. However, Oracle recommends that the client use SCAN to access the cluster. Clients Using SCAN can also use EZCONNECT to access the cluster. In addition to starting the local LISTENER listener on all nodes to listen to the local VIP, Grid Infrastructure also starts scan listener LISTENER_SCAN1 (up to three in a cluster) to listen to scan vip; oracle Database11gR2 sets local_listener to local LISTENER by default and remote_listener to SCAN listener. SCAN listener will be running off GRID_HOME, and by default, in 11gR2 local listener will be running off GRID_HOME as well. SCAN FAQs how to configure SCAN and SCAN listener? During "Typical installation", the program prompts you to confirm the default Single Client Access Name (SCAN ). If you change the default SCAN, the SCAN name you want to use must be unique. If the SCAN name is resolved to an IP address, the root script (root. sh or rootupgrade. sh) will create scan vip resources (ora. scan1.vip) and corresponding SCAN listener resources (ora. number of LISTENER_SCAN1.lsnr. For example, if the SCAN name can be resolved to two IP addresses, the root script will create two scan vip resources and two corresponding SCAN listener resources. Scan vip and corresponding SCAN listener work in pairs. When scan vip fails to another node, the corresponding SCAN listener fails to the same node. When SCAN VIPfailover occurs, always select the node with the least number of VIPs to run. For example, in a 4-node cluster, if scan vip runs on node, node 2, and node 3, when Node 3 is down, the scan vip on node 3 and the corresponding SCAN listener will failover to node 4, because a scan vip has been run on each of the other two nodes. We can also use "srvctl" to add/modify SCAN vip and listener. Do you still need to configure locallistener on each node? The answer is "yes". We still need to configure an independent local listener on each node. SCAN listener does not replace the local listener on each node. In 11g R2 GI, three new scan listener will be run on all nodes in the cluster. If there are more than three cluster nodes, only SCAN listener is run on three of the nodes. No matter how many nodes are in the cluster, only three scan listener instances can be run. The database registers the parameter to SCAN listener through remote_listener initialization. If any scan listener in the cluster fails, it will be automatically restarted on a new node. When the client submits a request, the SCANlistener listening on the scan vip address and port will establish a connection on behalf of the client. Because all services on the cluster have been registered to SCAN listener, SCAN listener will have the least load nodes (each scan listener will update the load statistics of the cluster in real time) the local listener address on is returned to the client. Finally, the client establishes a connection with the service by using the local listener on the node that provides the service. All these operations are transparent to the client, and no explicit configuration is required on the client. $ SRVCTL STATUSSCAN_LISTENERSCAN restart is enabledSCAN restart is running on node TEST1SCAN restart is enabledSCAN restart is running on node TEST2SCAN restart is enabledSCAN restart is running on node TEST3 can be parsed using '/etc/hosts'? SCAN instead of DNS or GNS? We strongly recommend that you do not configure the scan vip address in the hosts file. However, you can use the hosts file to parse the SCAN name, but only one scan ip address can be parsed. If you use the hosts file to parse the SCAN name, The ClusterVerification Utility failure error will occur at the end of the installation. For details, see metalink Article NOTE 887471.1. Can I use the previous connection method (VIP) for client connection? The client can still access the cluster using the connection method (VIP) of the previous version. Oracle strongly recommends that the client use SCAN to access the cluster. Clients Using SCAN can also access the cluster through EZCONNECT. Do I have to use SCAN? It is strongly recommended. It is not necessary. Does the SCAN function support deletion? SCAN a Component of Oracle 11gR2 Grid Infrastructure. SCAN cannot be deleted. Sample TNS entry for scan test. ORACLE. COM = (DESCRIPTION = (ADDRESS = (PROTOCOL = tcp) (HOST = SCAN-TEST.ORACLE.COM) (PORT = 1521) (CONNECT_DATA = (SERVICE_NAME = 11GR2TEST. ORACLE. COM) Sample TNS Entry without scan test. ORACLE. COM = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = tcp) (HOST = TEST1-vip.ORACLE.COM) (PORT = 1521) (ADDRESS = (PROTOCOL = tcp) (HOST = TEST2-vip.ORACLE.COM) (PORT = 1521) (CONNECT_DATA = (SERVICE_NAME = 11GR2TEST. ORACLE. COM )))