RAC Load Balancing, TAF , FAN

Client Side Connect-Time Load Balance : ****************

The client load balancing feature enables clients to randomize connection requests among the listeners.
This is done by client Tnsnames Parameter: LOAD_BALANCE.
The (load_balance=yes) instructs SQLNet to progress through the list of listener addresses in the address_list section of the net service name in a random sequence. When set to OFF, instructs SQLNet to try the addresses sequentially until one succeeds.



Client Side Connect-Time failover : ***********************************

This is done by client Tnsnames Parameter: FAILOVER
The (failover=on) enables clients to connect to another listener if the initial connection to the first listener fails. Without connect-time failover, Oracle Net attempts a connection with only one listener.



Server Side Listener Connection Load Balancing. ****************************

With server-side load balancing, the listener directs a connection request to the best instance currently providing the service.
Init parameter remote_listener should be set. When set, each instance registers with the TNS listeners running on all nodes within the cluster.


There are two types of server-side load balancing:

Load Based — Server side load balancing redirects connections by default depending on node load. This id default.

Session Based — Session based load balancing takes into account the number of sessions connected to each node and then distributes the connections to balance the number of sessions across the different nodes.

From 10g release 2 the service can be setup to use load balancing advisory. This mean connections can be routed using SERVICE TIME and THROUGHPUT. Connection load balancing means the goal of a service can be changed, to reflect the type of connections using the service.

Transparent Application Failover (TAF) : *******************************

Transparent Application Failover (TAF) is a feature of the Oracle Call Interface (OCI) driver at client side. It enables the application to automatically reconnect to a database, if the database instance to which the connection is made fails. In this case, the active transactions roll back.
Tnsnames Parameter: FAILOVER_MODE

e.g (failover_mode=(type=select)(method=basic))
Failover Mode Type can be Either SESSION or SELECT.


Session failover will have just the session to failed over to the next available node. With SELECT, the select query will be resumed.
TAF can be configured with just server side service settings by using dbms_service package.

Fast Connection Failover (FCF)

Fast Connection Failover is a feature of Oracle clients that have integrated with FAN HA Events.
Oracle JDBC Implicit Connection Cache, Oracle Call Interface (OCI), and Oracle Data Provider for .Net (ODP.Net) include fast connection failover.

With fast connection failover, when a down event is received, cached connections affected by the down event are immediately marked invalid and cleaned up