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FAQ: Does ArcGIS support Oracle's Transparent Application Failover (TAF)?

Question

Does ArcGIS support Oracle's Transparent Application Failover (TAF)?

Answer

Oracle's Transparent Application Failover (TAF) provides the ability for client applications to transparently failover to a second instance when the Oracle instance, that the session is currently connected to, fails.

There are several limitations when using Oracle TAF. See the Oracle MetaLink document 97926.1 "Failover Issues and Limitations" for additional information. The following list contains the primary reasons why ArcGIS, including read-only applications, cannot support TAF:

1. In progress or active transactions are automatically rolled back. The client application is therefore required to 're-apply' all changes since the last successful commit point.

2. All PL/SQL package states are lost.

3. All ALTER SESSION statements are lost.

4. Continuing work on existing cursors may raise an error. For example, "ORA-25401 cannot continue fetches".

5. Failed over selects may raise an error.

6. All rows in global temporary tables are lost and removed upon the connection's exit.

7. All reference to cursors (SQL statement handles) that the session is explicitly holding are lost.

8. Sessions do not transparently failover when the server node dies, while the session is waiting for a response.

Oracle's TAF appears to be a powerful mechanism in supporting high available (HA) systems, but for complex and intelligent applications, such as ArcGIS, it does not meet all the requirements for a truly transparent failover mechanism.

If future enhancements are made within the TAF architecture, ESRI will revisit the ability to support TAF.

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