Transparent Application Failover (TAF) Callback Support in Oracle Data Provider for .NET

• Objective of the Sample Application
• Overview of the Sample Application
• User Notes with Screen Shots
• Required Software
• Extracting the Sample
• Database Setup
• Preparing and Running the Sample 
• Description of Sample files 

This purpose of this sample is to demonstrate TAF (Transparent Application Failover) with a C# application, when the connection to a database is severed.

FailoverEvent.Begin  : Indicates that failover has detected a lost connection and failover is starting. 

FailoverEvent.End    : Indicates successful completion of failover. 

FailoverEvent.Abort  : Indicates that failover was unsuccessful and there is no option of retrying. 

FailoverEvent.Reauth : Indicates that a user handle has been re-authenticated.

FailoverEvent.Error  : Indicates that an error occurred while trying to re-establish the connection.

1. The sample at start up displays the form with blank data grid. When "Get Product Data" button is clicked, the data is fetched from the database and displayed to user as shown in Fig. 1

   

                                       Fig. 1

• Visual C# installed with MS Development Environment 7.0 version (MS Visual Studio .NET)  including MS .NET Framework 1.0 version

• Oracle8i Database or later running SQL*Net TCP/IP listener (can be downloaded here)

• Oracle Data Provider for .NET (ODP.NET) (can be downloaded here)

Unzip TAFSample.zip using Winzip or command utility to your convenient directory. Extraction of the zip file results  in the creation of TAFSample directory.

Connect to your database as any user and run the script TAFSample\config\DatabaseSetup.sql at the SQL prompt.

@<Extract_Dir>\TAFSample\config\DatabaseSetup.sql

where <Extract_Dir> is the directory where you have extracted the sample.

The script creates an user "OraNet" with password "OraNet".

It creates a PRODUCTS table as below and populates it with data.

1. Ensure that the Database setup has been completed. 

2. The tnsnames.ora file should be suitably modified for your database entry so that TAF tries to reconnect when the database connection is lost. The tnsnames.ora file is located at <Oracle_Home>/network/Admin directory. Your database TNS entry should look like this :

   where <Oracle_Home> is the directory where your database or SQL* Plus client is installed. Replace the values for the database parameters highlighted in red color with your database parameters.

   <DBFAILOVER.US.ORACLE.COM> =
     (DESCRIPTION =
       (ADDRESS_LIST =
         (ADDRESS = (PROTOCOL = TCP)(HOST = <myhostname>)(PORT = <1521>))
       )
       (CONNECT_DATA =
   	    (SERVCE_NAME = <dbfailover>)
         (FAILOVER_MODE = (TYPE = SELECT) (METHOD = BASIC) (RETRIES=100)
   
         (DELAY=1))
   
       )
     )

3. Open TAFSample.sln using Visual Studio .NET from <Extract_Dir>\TAFSample folder.

4. Edit ConnectionParams.cs file to change the database connection parameters i.e.TNSName for database you want to use . Save this file.

5. Ensure that the following .NET Component References have been added to TAFSample project:

   • System
   • System.Data
   • System.Drawing
   • System.Windows.Forms
   • System.XML
   • Oracle.DataAccess.
   
   To add the above .NET Components 
   • Go to Menu -> View -> Solution Explorer.
   • Right click on TAFSample project, choose 'Add Reference'.
   • Choose the above .NET Components from the list displayed.
   • Click 'Select', then OK.
   • The chosen .NET component gets added to the project. 



6. Build and run the sample in Debug mode. (Please ensure to perform the following steps)

7. The sample when run, shows a form with a blank data grid. The user should click "Get Products Data" button to start fetching the product details from the database.

8. For demonstrating TAF, a breakpoint has been set in the source code just before the line where, OracleDataAdapter fills the DataSet with products data using the previously created connection. Because of this breakpoint, the execution of the query will be halted.

9. Now the user should restart the database from SQL* Plus using following command,

   
   To login as a DBA user,

   SQL> Connect sys/<your_sys_password>@<Your_TNSName> as sysdba


To shutdown and restart database

SQL> startup force

10. After restarting the database, the user should return to the application and continue the execution of application. The Failover event is called and the Failover handler method displays the appropriate messages in a message box and in the status bar of application.

11. The query will be executed again against the database using a new connection, data fetched and displayed in the data grid.

Please enter your comments on this sample in OTN Sample Code Discussion Forum.