Oracle HA (High Availability) events allow quickly informing client applications that an Oracle Real Application Clusters (RAC) service, service member, instance, or node goes down because of a failure or other reason. Note that you need to set the OracleConnectionStringBuilder.HAEvents connection string parameter to true in order to receive HA events.

Please note that this event is not supported in the OracleConnection.Direct mode. It is supported for Oracle Client 10g and higher. For Oracle Client 10g this event can be received only when you have at least one active connection to the Oracle database service, service member, instance, or node that goes down. For Oracle Client 11 and higher this event is received regardless of a presence of active connections to the event source.

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

OracleConnection Class
OracleConnection Members
OracleHAEventArgs Class
OracleHAEventHandler Delegate