7
Oracle Virtual IP Address
Since Oracle 10g, clients use a Virtual IP Address (VIP) to connect to the database. The VIP is a static
IP which is defined in the Oracle Clusterware installation.
When a RAC node fails, its associated VIP will failover automatically to one of the remaining nodes.
The new node hosting the failed VIP will associate a new MAC address for this VIP and will make it
known outside.
When clients are not using a VIP for their connections, in case of node failure, they run in a TCP
timeout. For availability and failover purposes, we have defined a VIP on each RAC node (ita018-vip,
ita021-vip, ita022-vip and ita023-vip). We will use the VIP to configure the integration, thus
providing Failover capabilities.
Oracle Services to manage workloads
Applications using an RAC database need to have their workload managed across the entire cluster.
For this purpose, Oracle introduced the Workload Management framework. Based on the use of
Services, it presents the application using the cluster an interface for managing their load in a very
simple way.
Oracle Services allow breaking down workloads in a manageable way, based on Service Level
Agreements, High Availability needs, or business needs and route them to the optimal instances
assigned. It is recommended to group load with the same service level. Load balancing among the
available instances is provided by Oracle Net Services.
When defining a new service, we can specify on which RAC instances the service should run on:
•
Preferred:
service should run on this instance
•
Available:
service should run on this instance if a preferred fails
•
Not Used:
the service should not use this instance
Transparent Application Failover (TAF) enables Oracle Net to failover to a different listener. Based on
the TAF method, the services can be defined as:
•
None:
•
Basic:
connection to failover server will be established at failover time
•
Preconnect:
pre-established connections are allocated to provide faster failover
Oracle Services definition
To define a new service, you can use the command line interface, srvctl, or the database
configuration assistant, dbca:
$ srvctl add service –d RAC –s BACKUP –r RAC1,RAC2,RAC3,RAC4 –P PRECONNECT
In the above example, we add a new service called BACKUP in the database RAC. With the option –
r we specified the list of preferred instances and the option –P specifies the TAF policy.
The same can be achieved using the Database Configuration Assistant (dbca) GUI:
