Measures reported by OraRacLisCTTest

Oracle RAC 11g release 2 introduces the Single Client Access Name (SCAN), which provides a single name for clients to access Oracle Databases running in a cluster and simplify the database connection strings that an Oracle Client uses to connect.

The RAC components that play a crucial role in SCAN are as follows:

• SCAN VIP: SCAN VIPs are physical IP addresses that you allocate to a SCAN listener.

• SCAN Listener: SCAN Listener is an Oracle RAC component, which starts running a service on the port [default 1521] using IP address assigned to SCAN VIPs. The name that is given to a SCAN Listener is referred as SCAN name, which should be registered in DNS server.

• Node VIP: Each node in the RAC cluster has its own node VIP. It is a high availability resource of RAC that enables a client to initially connect to the database service on its node or to fail over to another cluster node and advise that its node is down.

SCAN listeners can run on any node in the cluster. Typically, each cluster will have a minimum of 1 and a maximum of 3 SCAN listeners, regardless of the number of nodes in the cluster. Three SCAN listeners are recommended considering load balancing and high availability requirements. A SCAN listener can be started only when the SCAN VIPs are online. The root.sh script automatically configures the SCAN VIPs and SCAN listeners. When the root.sh is run on the first node, all 3 scan IPs are plugged on to the first node's public interface. The SCAN/VIP combination will failover to another node in the cluster, if the current node fails. Besides performing failover, SCAN also load balances across the instances providing a service, by selecting and routing requests to the least loaded node.

To evaluate the load balancing ability of the SCAN listeners in a cluster and promptly detect inconsistencies, administrators should continuously monitor the connection traffic to each node in the cluster and quickly identify the over-utilized / under-utilized nodes. This can be achieved using the OraRacLisCTTest. This test auto-discovers the nodes in an RAC cluster and reports the rate at which each node successfully services connection requests. In the process, the test pinpoints the following:

• Nodes handling more connections per second than the rest, and;

• Nodes handling very few connections when compared to the other nodes

Such anomalies indicate that the SCAN listeners are not performing load balancing efficiently.

Outputs of the test: One set of results for every node in the cluster.

The measures made by this test are as follows: