High Availability (HA) events are generated when resources change state within an Oracle Clusterware environment. Oracle Notification Service (ONS) is a facility that creates a bridge with middle-tier servers or applications to transport these events to application logic for handling or reaction. ONS is part of a larger framework known as Fast Application Notification (FAN). With FAN, applications use these events to achieve very fast detection of failures and re-balancing of connection pools, following failures and recovery. When FAN is used with an Oracle Database, the Advanced Queuing (AQ) feature allows HA events to be received by external applications such as .NET clients. The easiest way to receive all the benefits of FAN, with no effort, is to use a client that is integrated with FAN, such as:
- Java Database Connectivity (JDBC) Implicit Connection Cache
- User-extensible callouts
- Connection Manager (CMAN)
- Listeners
- Oracle Notification Service (ONS) API
- OCI Connection Pool or Session Pool
- Transparent Application Failover (TAF)
- ODP.NET Connection Pool
Note: Not all these applications can receive all types of FAN events and can use Oracle Notification Service.