What is SCAN in RAC?

SCAN (Single Client Access Name) is a feature in Oracle RAC that provides a single hostname for clients to connect to the RAC database, regardless of how many nodes are in the cluster.

Instead of configuring clients with multiple node IPs, they connect using one SCAN name, and Oracle automatically routes connections to the appropriate RAC node.

Benefits:

• Simplifies client configuration
• Provides load balancing
• Supports node additions/removals without client changes
• Improves high availability

How SCAN Works

• Client connects to SCAN name.
• DNS resolves the SCAN name to one of the SCAN IPs.
• SCAN Listener receives the request.
• SCAN Listener redirects the client to the least-loaded RAC node.
• Client establishes a connection with that node's local listener.

SCAN Requirements

Oracle recommends:

• 1 SCAN Name
• 3 SCAN IP Addresses (for redundancy)

Advantages of SCAN

• Single connection string for applications
• Automatic load balancing
• Easier RAC administration
• Supports cluster expansion without application changes
• Improved failover capabilities