Oracle Grid Infrastructure SCAN (single customer access name)

Scan's primary role is to simplify the configuration of the client connection database, regardless of whether the cluster increases or deletes the node scan name remains unchanged, and the client does not need to make any modifications.

Scan is a name that is resolved to a maximum of 3 IP addresses via DNS (scan VIP)

The SCAN VIP must be in the same subnet as the cluster's public network resources.

Scan VIP is distributed evenly across the nodes of the cluster, for example: a cluster of 8 nodes, select 3 nodes to run scan VIP, when the node running scan VIP is having problems, scan VIP will drift to other normal nodes, for a two node cluster, If 3 scan VIPs are configured, there will be one node with two scan VIPs, and the other node has a scan VIP.

The role of scan VIP is to receive client connections, each scan VIP will have a corresponding scan LISTENER, and scan LISTENER will only listen to the corresponding scan VIP, and they must be running on the same node.

Scan VIP and Scan listener in the form of cluster resources, unified management by the agent process of the cluster, scan VIP depends on the cluster of public network resources, and Scan listener relies on the corresponding scan VIP resources, when the local node problem scan After the VIP drifts to other nodes, the corresponding scan listener also needs to drift along with the scan VIP.

Connect to a database via scan

Phase 1: The Pmon process for each node registers the service provided by the local instance to the local node's listener and each scan listener by accessing the database information. Where Local_listener specifies the local listener location that Pmon needs to register, and Remote_listener specifies the scan listener location that needs to be registered, and then, regardless of the listener on the local node, Or the scan listener is ready to connect to the receiving client.

Phase 2: The client initiates a connection to the scan listener through an alias in Tnsnames.ora, because the scan listener is distributed across different nodes in the cluster, which node depends on which node the DNS resolves the scan name to VIP (DNS uses polling to return the IP address of the scan).

Phase 3:scan listener after receiving the request sent by the client, according to the responsibility of each node, forward the client connection to the least-loaded node local listener, and then the local listener of the corresponding node to complete the connection with the client

Scan is similar to a connecting middle tier, and Oracle RAC actually implements the server-side balancing function through scan.

Oracle Grid Infrastructure SCAN (single customer access name)