Fast Application Notification (FAN) is a high availability and load balancing notification mechanism that Oracle RAC, Data Guard, and GoldenGate use to notify ODP.NET applications about cluster configuration and service-level information, including status changes such as UP or DOWN events and server load. FAN UP and DOWN events can apply to instances, services, and nodes. Based on information received, ODP.NET can adjust its connection pool accordingly to improve application availability and performance.

With FAN, Oracle RAC, Data Guard, and GoldenGate use one of two Oracle messaging infrastructures to send notifications to ODP.NET applications:

• Oracle Notification Service (ONS)

• Oracle Database Advanced Queueing (AQ).

Table 3-5 describes when each messaging system is used and the ODP.NET-related client configuration.

For automatic ONS configuration, developers can add more nodes and ports for ODP.NET to listen to, in addition to the nodes and ports that ODP.NET obtains from the database automatically.

ODP.NET applications do not require code changes to migrate from the AQ to ONS FAN infrastructure. However, some ODP.NET client configuration changes may be necessary when migrating to ONS, a newer database server version, or from ODP.NET, Unmanaged Driver to the managed driver, as documented above.

On the database server side, FAN must be set up and configured.

Using FAN Messages from the database, ODP.NET can do the following:

• With Runtime Connection Load Balancing, ODP.NET load balances connections among Oracle RAC nodes, services, and service members and GDS resources. This feature improves ODP.NET response time and ensures better resource allocation of server resources.

• With the Fast Connection Failover (FCF) feature, Oracle RAC, Data Guard, and GoldenGate can inform the ODP.NET connection pool if database nodes, services, service members, or the databases have gone down. These DOWN messages indicate which connections in the pool are invalid and must be removed.

With Runtime Connection Load Balancing, Oracle Data Provider for .NET balances work requests across Oracle RAC instances based on the load balancing advisory and service goal. Because workloads can constantly change, load balancing occurs when the application requests a new connection. Thus, ODP.NET optimizes service levels by connecting users to the least loaded nodes in real-time.

In Oracle Database 12c, Runtime Connection Load Balancing has been extended to Oracle Data Guard and Oracle GoldenGate so that ODP.NET 12c connections can be load balanced with these two database services as part of Global Data Services. No ODP.NET applications require code changes to use Global Data Services if they are already using Runtime Connection Load Balancing.

When Runtime Connection Load Balancing is enabled:

• The ODP.NET connection pool dispenses connections based on the load balancing advisory and service goal.

• The ODP.NET connection pool also balances the number of connections to each service member providing the service, based on the load balancing advisory and service goal.

By default, ODP.NET is enabled to receive Runtime Connection Load Balancing FAN messages from the server. The feature has been enabled via the "Load Balancing=true" and "pooling=true" settings in the connection string, which are the default values. This feature can only be used if "pooling=true". In order to use Runtime Connection Load Balancing, specific Oracle server configurations must be set.

The following connection string example enables Runtime Connection Load Balancing:

"user id=scott;password=tiger;data source=erp;load balancing=true;"

When an Oracle RAC service, service member, node, or a Data Guard database fails, the severed ODP.NET connection objects may continue to exist in the application. If users attempt to use these invalid connections, they will encounter errors. FCF enables ODP.NET to free these severed connections proactively and quickly. Users then will be able to use the application after a server side failure without manual intervention from an administrator.

In Oracle Database 12c, FCF has been extended to Oracle Data Guard and Oracle GoldenGate for ODP.NET 12c connections through Global Data Services. No ODP.NET applications require code changes to use Global Data Services if they already use FCF.

ODP.NET applications can enable FCF through the High Availability Events, "HA Events", connection string attribute. When HA Events are enabled:

• ODP.NET connection pool proactively removes connections from the pool when a Global Data Service or Oracle RAC service, service member, node, or database goes down.

• ODP.NET proactively forces threads waiting for responses from the downed database to exit out from the existing call to avoid any hangs. When such a connection is then returned to the pool, any resource associated with that connection is freed.

• ODP.NET establishes connections to existing Oracle instances if the removal of severed connections brings the total number of connections below the "min pool size", upon the next connection request.

By default, ODP.NET is enabled to receive FCF FAN messages from the server. This feature have been enabled via the HA Events=true and pooling=true settings in the connection string, which are the default values.

The following connection string example enables HA Events:

"user id=scott;password=tiger;data source=erp;HA events=true;"

FCF not only provides high availability services for unplanned outages, such as node failures, but also for planned outages, such as server repairs, upgrades, and changes, to minimize service disruption to ODP.NET application users.

When a database service is set to be stopped or relocated, a FAN message is published with a planned reason code. A FCF-aware ODP.NET connection pool (HA Events=true) receives the notification and commences to close idle connections, no longer allowing new connections to that specific database service. Active connections to that specific database service remain until users complete their tasks and the connection is returned to the pool. Thus, no users must stop work mid-stream due to a planned outage.

Eventually, all users complete their tasks and no connections remain to that database service. The database administrator can then stop the service for the planned outage task. This feature allows the database service to be stopped as quickly as possible without end user disruption.

Oracle planned outage support works with Oracle Real Application Clusters (Oracle RAC), Oracle Data Guard, and some single instance scenarios.

SWITCHOVER TO <database name> [WAIT <timeout in seconds> ];  

When connection pools are created for a single-instance database, pool size attributes are applied to the single service. Similarly, when connection pools are created for an Oracle RAC database, the pool size attributes are applied to a service and not to service members. For example, if "Min Pool Size" is set to N, then ODP.NET does not create N connections for each service member. Instead, it creates, at minimum, N connections for the entire service, where N connections are distributed among the service members.

The following pool size connection string attributes are applied to a service.

• Min Pool Size

• Max Pool Size

• Incr Pool Size

• Decr Pool Size

ODP.NET connects to the same Oracle RAC node when required by a distributed transaction that has already begun on a particular node, by an Oracle runtime connection load balancing advisory, or by Oracle RAC load balancing gravitation in which connections will gravitate to an under utilized node. If the connection pool has no idle connections to this particular node, then ODP.NET will create a new connection to this node. Node affinity is honored even when the connection pool runs out of idle connections to dispense.