Database Reference
In-Depth Information
Both SQL Plus and the JDBC Type 4 connection methods use the TNS technology to establish connection to the
database. JDBC Type 2 driver, primarily used in Java applications, converts the JDBC invocations to call the OCI driver,
which is then sent over Oracle Net to the Oracle database. Type 2 drivers do not use the TNS technology.
Oracle Protocol Support Layer
This layer acts as an interface between the ONFL and the industry standard network protocols such as the TCP/IP,
named pipes, and so forth.
Listeners
There are two types of listeners in an Oracle Database 11g Release 2 RAC configuration.
SCAN Listeners
Single Client Access Name (SCAN) is a new feature introduced in Oracle Database 11g that provides a single name
for clients to access Oracle databases running on the cluster. Similar to the single level cluster alias that existed in the
virtual memory system (VMS) and Tru64 clustered environments, the SCAN provides a single address reference to the
entire cluster. Similar to the cluster alias, the SCAN also has intelligence built into it for load balancing and failover
from client connections to the database.
To configure a SCAN reference to the cluster, the network administrator maps one host reference that maps to
three physical IPs definitions in the domain name system (DNS).
During cluster configuration, for each of the three IP addresses that the SCAN resolves to, a SCAN VIP resource
is created and a SCAN listener is created. The SCAN listener is dependent on the )SCAN VIP and the three SCAN VIPs
will be dispersed across the cluster. Assuming that a cluster consists of three or more nodes, each pair of resources is
started on a different server in the cluster:
[mvallath@prddb1 mysql]$ nslookup prddb-scan
Server: 10.62.85.12
Address: 10.62.85.12#53
Name: prddb-scan.summersky.biz
Address: 10.62.70.13
Name: prddb-scan.summersky.biz
Address: 10.62.70.14
Name: prddb-scan.summersky.biz
Address: 10.62.70.15
In Figure 11-1 , when the connection request is received from the client via the network interface to the database
server, the SCAN listener receives (illustrated in Figure 11-2 ) the request and redirects the connection to the local
listener on the node where the least loaded instance is running. In a RAC configuration, a node needs at least one
network adapter that provides the interface (e.g., an Ethernet adapter) to the local area network (LAN) that allows
users/applications to connect and query data from the database. This is normally considered as the public network
interface. Public network adapters are visible to users external to the node participating in the cluster. Network
adapters are identified by an Internet static IP address, which is assigned during O/S configuration.
 
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