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Thread: FAN Objectives in Oracle RAC

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    FAN Objectives in Oracle RAC

    Fast Application Notification (FAN), is a feature of Oracle Real Application Clusters (RAC)
    that further differentiates it for high availability and scalability.

    FAN enables the automated recovery of applications when cluster components fail. FAN solves the following problems:

    • Applications waiting for TCP/IP time-outs when a node fails.

    • Applications attempting to connect when services are down.

    • Applications not connecting when services resume.

    • Applications processing the last result after a node, instance, or service has gone
    down.

    • Applications not balancing across available systems when services restart or expand.

    • Attempting to execute work on slow, hung, and dead nodes

    For cluster configuration changes, the Oracle RAC HA framework posts a FAN event
    immediately when a state change occurs in the cluster. Instead of waiting for the Application Tier to poll the Database Tier and find a problem, using FAN your application tier will receive these events and react immediately to the event.

    For down events, the disruption to the application can be minimized as connections to the failed instance or node can be terminated. In-flight transactions are terminated and the application user immediately notified. Application users requesting connections are directed to available instances only.

    Applications can take advantage of the load balancing advisory FAN events to direct work requests to the instance in the cluster that is currently providing the best service.

    The use of FAN requires the use of Services. Services decouple any hardwired mapping between a connection request and a RAC instance. Services are an entity defined for a RAC database that allows the workload for a RAC database to be managed. Services divide the entire workload executing in the Oracle Database into mutually disjoint classes.

    To understand Services , and setup service to use TAF and FAN , refer to :
    Overview-and-Setup-of-Services-in-RAC

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