RAC Load Balancing

1. What are the types of connection load-balancing?

There are two types of connection load-balancing:

server-side load balancing and client-side load balancing.

2. Difference between server-side and client-sideload balancing?

* Client-side balancing happens at client side where load balancing is done using listener.

* In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing the best service.

3. What is TAF? TAF allow client to continue working after the application loses in connection to the database After the instance failure and database recovery coplets , the application can automatically reconnect to one of the surviving instances and continue operation .

4. What is FAN? Its provactelly notify application regarding the status of the cluster and configuration changes that take place.

5. What is ONS? Oracle clusterware use ONS to send notification about the status of the database instance to middle tier application. ONS is a daemon process that communicates with ONS demons on other nodes which inform each other of the current status of the database component on database server.

6. When ONS act??

Its act in following condition:

* When Node Status Changes: ONS enables applications to receive notifications when the status of a node changes, such as when a node joins or leaves the cluster.

* Service Availability: ONS allows applications to subscribe to service availability events, so they can receive notifications when a service becomes available or unavailable.

* Database Failover: In the event of a database instance failure, Oracle RAC automatically performs a failover to another available instance.

* ONS plays a vital role in facilitating this failover process by notifying applications about the instance failure and the new primary instance to which they should connect.

6. What is the Load Balancing Advisory? To assist in the balancing of application workload across designated resources, Oracle Database provides the Load Balancing Advisory. This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage value of how much of the total workload should be sent to this instance as well as service quality flag. The feedback is provided as an entry in the Automatic Workload Repository and a FAN event is published. The easiest way for an application to take advantage of the load balancing advisory, is to enable Runtime Connection Load Balancing with an integrated client.

7. How do I enable the load balancing advisory?

The load balancing advisory requires the use of services and Oracle Net connection load balancing.

To enable it, on the server: set a goal (service_time or throughput, and set CLB_GOAL=SHORT ) on your service.

For client, you must be using the connection pool.

For JDBC, enable the datasource parameter FastConnectionFailoverEnabled.

For ODP.NET enable the datasource parameter Load Balancing=true.

9. Can I use TAF with e-Business in a RAC environment? TAF itself does not work with e-Business suite due to Forms/TAF limitations, but you can configure the tns failover clause. On instance failure, when the user logs back into the system, their session will be directed to a surviving instance, and the user will be taken to the navigator tab. Their committed work will be available; any uncommitted work must be re-started.