Sometimes, you don't  have the possiblity enable Transparent application failover on the client side (in the tnsnames.ora file for example).

That's where this new feature in Oracle 10gR2 RAC comes handy:

You can enable both failover and load-balancing on the server side, by executing a simple dbms_service procedure.

EXECUTE DBMS_SERVICE.MODIFY_SERVICE (service_name => 'MY_SERVICE_NAME'
, aq_ha_notifications => TRUE
, failover_method => DBMS_SERVICE.FAILOVER_METHOD_BASIC
, failover_type => DBMS_SERVICE.FAILOVER_TYPE_SELECT
, failover_retries => 60
, failover_delay => 10
, clb_goal => DBMS_SERVICE.CLB_GOAL_LONG);


To disable the feature, it's as simple:

begin
    dbms_service.modify_service(
      service_name=>'MY_SERVICE_NAME',
      failover_type=>DBMS_SERVICE.FAILOVER_TYPE_NONE,
      failover_method=>DBMS_SERVICE.FAILOVER_METHOD_NONE
    );
  end;
/


For complete documentation, you can check:

http://download.oracle.com/docs/cd/B19306_01/rac.102/b14197/hafeats.htm#BABIAICG


Happy computing,

Nixman