Configuring Oracle Database Gateway for ODBC

After installing the gateway and the ODBC driver for the non-Oracle system, perform the following tasks to configure Oracle Database Gateway for ODBC:

11.1 Configure the Gateway Initialization Parameter File

Perform the following tasks to configure the gateway initialization file:

11.1.1 Create the Initialization Parameter File

You must create an initialization file for your Oracle Database Gateway for ODBC. Oracle supplies a sample initialization file, initdg4odbc.ora. The sample file is stored in the ORACLE_HOME\hs\admin directory.

To create an initialization file for the ODBC gateway, copy the sample initialization file and rename it to initsid.ora, where sid is the system identifier(SID) you want to use for the instance of the non-Oracle system to which the gateway connects.

The gateway system identifier (SID) is an alphanumeric character string that identifies a gateway instance. You need one gateway instance, and therefore one gateway SID, for each ODBC source you are accessing.

If you want to access two ODBC sources, you need two gateway SIDs, one for each instance of the gateway. If you have only one ODBC source but want to access it sometimes with one set of gateway parameter settings, and other times with different gateway parameter settings, then you will need multiple gateway SIDs for the single ODBC source. The SID is used as part of the file name for the initialization parameter file.

11.1.2 Set the Initialization Parameter Values

After the initialization file has been created, you must set the initialization parameter values. A number of initialization parameters can be used to modify the gateway behavior. You must set the HS_FDS_CONNECT_INFO initialization parameter. Other initialization parameters have defaults or are optional. You can use the default values and omit the optional parameters, or you can specify the parameters with values tailored for your installation. Changes made to the initialization parameters only take effect in the next gateway session.

The HS_FDS_CONNECT_INFO initialization parameter specifies the information required for connecting to the non-Oracle system. Set the HS_FDS_CONNECT_INFO as follows:

HS_FDS_CONNECT_INFO=dsn_value

where dsn_value is the name of the system DSN defined in the Microsoft Windows ODBC Data Source Administrator.

Note:

Before deciding whether to accept the default values or to change them.

11.1.2.1 Example: Setting Initialization Parameter Values

Assume that a system DSN has been defined in the Microsoft Windows ODBC Data Source Administrator. In order to connect to this SQL Server database through the gateway, the following line is required in the initsid.ora file:

HS_FDS_CONNECT_INFO=sqlserver7

sqlserver7 is the name of the system DSN defined in the Microsoft Windows ODBC Data Source Administrator.

The following procedure enables you to define a system DSN in the Microsoft Windows ODBC Data Source Administrator, version 3.5:

1. From the Start menu, choose Settings > Control Panel and select ODBC.
2. Select the System DSN tab page to display the system data sources.
3. Click Add.
4. From the list of installed ODBC drivers, select the name of the driver that the data source will use. For example, select SQL Server.
5. Click Finish.
6. Enter a name for the DSN and an optional description. Enter other information depending on the ODBC driver. For example, for SQL Server enter the SQL Server machine name.

Note:

The name entered for the DSN must match the value of the initialization parameter HS_FDS_CONNECT_INFO that is specified in initsid.ora.

7. Refer to your ODBC driver documentation and follow the prompts to complete configuration of the DSN.
8. After creating the system DSN, click OK to exit the ODBC Data Source Administrator.

Note:

If the ODBC driver supports Quoted Identifiers or Delimited Identifiers it should be turned on.

11.2 Configure Oracle Net for the Gateway

The gateway requires Oracle Net to communicate with the Oracle database. After configuring the gateway, perform the following tasks to configure Oracle Net to work with the gateway:

11.2.1 Configure Oracle Net Listener for the Gateway

The Oracle Net Listener listens for incoming requests from the Oracle database. For the Oracle Net Listener to listen for the gateway, information about the gateway must be added to the Oracle Net Listener configuration file, listener.ora. This file by default is located in ORACLE_HOME\network\admin, where ORACLE_HOME is the directory under which the gateway is installed.

The following entries must be added to the listener.ora file:

• A list of Oracle Net addresses on which the Oracle Net Listener listens
• The executable name of the gateway that the Oracle Net Listener starts in response to incoming connection requests

A sample of the listener.ora entry (listener.ora.sample) is available in the ORACLE_HOME\dg4odbc\admin directory where ORACLE_HOME is the directory under which the gateway is installed.

11.2.1.1 Syntax of listener.ora File Entries

The Oracle database communicates with the gateway using Oracle Net and any supported protocol adapters. The following is the syntax of the address on which the Oracle Net Listener listens using the TCP/IP protocol adapter:

LISTENER=

        (ADDRESS=

          (PROTOCOL=TCP)

          (HOST=host_name)

          (PORT=port_number))

Where:

Variable	Description
host_name	is the name of the machine on which the gateway is installed.
port_number	specifies the port number used by the Oracle Net Listener. If you have other listeners running on the same machine, then the value of port_number must be different from the other listeners' port numbers.

To direct the Oracle Net Listener to start the gateway in response to incoming connection requests, add an entry to the listener.ora file.

Note:

You must use the same SID value in the listener.ora file and the tnsnames.ora file that will be configured in the next step.

SID_LIST_LISTENER=

   (SID_LIST=

      (SID_DESC=

         (SID_NAME=gateway_sid)

         (ORACLE_HOME=oracle_home_directory)

         (PROGRAM=dg4odbc)

      )

   )

Where:

Variable	Description
gateway_sid	specifies the SID of the gateway and matches the gateway SID specified in the connect descriptor entry in the tnsnames.ora file.
oracle_home_directory	specifies the Oracle home directory where the gateway resides.
dg4odbc	specifies the executable name of the Oracle Database Gateway for ODBC.

If you already have an existing Oracle Net Listener, then add the following syntax to SID_LIST in the existing listener.ora file:

SID_LIST_LISTENER=

(SID_LIST=

   (SID_DESC=.

     .

   )

   (SID_DESC=.

     .

   )

   (SID_DESC=

      (SID_NAME=gateway_sid)

      (ORACLE_HOME=oracle_home_directory)

      (PROGRAM=dg4odbc)

   )

)

11.2.2 Stop and Start the Oracle Net Listener for the Gateway

You must stop and restart the Oracle Net Listener to initiate the new settings, as follows:

1. From the Start menu, select Settings, Control Panel and then select Services.
2. Select the Oracle Net Listener service for the gateway.
3. If the service is already running, click Stop to stop it.
4. Click Start to start or restart the service.

11.3 Configure the Oracle Database for Gateway Access

Before you use the gateway to access an ODBC data source you must configure the Oracle database to enable communication with the gateway over Oracle Net.

To configure the Oracle database you must add connect descriptors to the tnsnames.ora file. By default, this file is in ORACLE_HOME\network\admin, where ORACLE_HOME is the directory in which the Oracle database is installed. You cannot use the Oracle Net Assistant or the Oracle Net Easy Config tools to configure the tnsnames.ora file. You must edit the file manually.

A sample of the tnsnames.ora entry (tnsnames.ora.sample) is available in the ORACLE_HOME\dg4odbc\admin directory where ORACLE_HOME is the directory under which the gateway is installed.

11.3.1 Configuring tnsnames.ora

Edit the tnsnames.ora file to add a connect descriptor for the gateway. The following is a syntax of the Oracle Net entry using the TCP/IP protocol:

connect_descriptor=

   (DESCRIPTION=

      (ADDRESS=

         (PROTOCOL=TCP)

         (HOST=host_name)

         (PORT=port_number)

      )

      (CONNECT_DATA=

         (SID=gateway_sid))

      (HS=OK))

Where:

Table 11-1 Gateway Parameters for tnsnames.ora File

Variable	Description
connect_descriptor	is the description of the object to connect to as specified when creating the database link, such as dg4odbc. Check the sqlnet.ora file for the following parameter setting: names.directory_path = (TNSNAMES) Note: The sqlnet.ora file is typically stored in ORACLE_HOME\network\admin.
TCP	is the TCP protocol used for TCP/IP connections.
host_name	specifies the machine where the gateway is running.
port_number	matches the port number used by the Oracle Net Listener that is listening for the gateway. The Oracle Net Listener's port number can be found in the listener.ora file used by the Oracle Net Listener..
gateway_sid	specifies the SID of the gateway and matches the SID specified in the listener.ora file of the Oracle Net Listener that is listening for the gateway. See
(HS=OK)	specifies that this connect descriptor connects to a non-Oracle system.

11.4 Create Database Links

Any Oracle client connected to the Oracle database can access an ODBC data source through the gateway. The Oracle client and the Oracle database can reside on different machines. The gateway accepts connections only from the Oracle database.

A connection to the gateway is established through a database link when it is first used in an Oracle session. In this context, a connection refers to the connection between the Oracle database and the gateway. The connection remains established until the Oracle session ends. Another session or user can access the same database link and get a distinct connection to the gateway and ODBC data source.

Database links are active for the duration of a gateway session. If you want to close a database link during a session, you can do so with the ALTER SESSION statement.

To access the ODBC data source, you must create a database link. A public database link is the most common of database links.

SQL> CREATE PUBLIC DATABASE LINK dblink CONNECT TO

2  "user" IDENTIFIED BY "password" USING 'tns_name_entry';

Where:

Variable	Description
dblink	is the complete database link name.
tns_name_entry	specifies the Oracle Net connect descriptor specified in the tnsnames.ora file that identifies the gateway

After the database link is created you can verify the connection to the ODBC data source, as follows:

SQL> SELECT * FROM DUAL@dblink;

11.5 Encrypt Gateway Initialization Parameter Values

The gateway uses user IDs and passwords to access the information in the remote database. Some user IDs and passwords must be defined in the gateway initialization file to handle functions such as resource recovery. In the current security conscious environment, having plain-text passwords that are accessible in the initialization file is deemed insecure. The dg4pwd encryption utility has been added as part of Heterogeneous Services to help make this more secure. This utility is accessible by this gateway. The initialization parameters that contain sensitive values can be stored in an encrypted form.

11.6 Configure the Gateway to Access Multiple ODBC Data Sources

The tasks for configuring the gateway to access multiple ODBC data sources are similar to the tasks for configuring the gateway for a single data source. The configuration example assumes the following:

• The gateway is installed and configured with the SID of dg4odbc.
• The gateway is configured to access one ODBC data source named dsn1.
• Two ODBC data sources named dsn2 and dsn3 where dsn2 and dsn3 are the names of the system DSN defined in the Microsoft Windows ODBC Data Source Administrator, are being added.

11.6.1 Multiple ODBC Data Sources Example: Configuring the Gateway

Choose One System ID for Each ODBC Data Source

A separate instance of the gateway is needed for each ODBC data source. Each instance needs its own gateway System ID (SID). For this example, the gateway SIDs are chosen for the instances that access the ODBC data source:

• dg4odbc2 for the gateway accessing data source dsn2.
• dg4odbc3 for the gateway accessing data source dsn3.

Create Two Initialization Parameter Files

Create an initialization parameter file for each instance of the gateway by copying the original initialization parameter file: ORACLE_HOME\hs\admin\initdg4odbc.ora, twice, naming one with the gateway SID for dsn2 and the other with the gateway SID for dsn3:

> cd ORACLE_HOME\hs\admin

> copy initdg4odbc.ora initdg4odbc2.ora

> copy initdg4odbc.ora initdg4odbc3.ora

Change the value of the HS_FDS_CONNECT_INFO parameter in the new files as follows:

For initdg4odbc2.ora, enter the following:

HS_FDS_CONNECT_INFO=dsn2

For initdg4odbc3.ora, enter the following:

HS_FDS_CONNECT_INFO=dsn3

Note:

If you have multiple gateway SIDs for the same ODBC data source because you want to use different gateway parameter settings at different times, follow the same procedure. You create several initialization parameter files, each with different SIDs and different parameter settings.

11.6.2 Multiple ODBC Data Sources Example: Configuring Oracle Net Listener

Add Entries to listener.ora

Add two new entries to the Oracle Net Listener configuration file, listener.ora. You must have an entry for each gateway instance, even when multiple gateway instances access the same database.

The following example shows the entry for the original installed gateway first, followed by the new entries:

SID_LIST_LISTENER=

(SID_LIST=

   (SID_DESC=

      (SID_NAME=dg4odbc)

      (ORACLE_HOME=oracle_home_directory)

      (PROGRAM=dg4odbc)

   )

   (SID_DESC=

      (SID_NAME=dg4odbc2)

      (ORACLE_HOME=oracle_home_directory)

      (PROGRAM=dg4odbc)

   )

   (SID_DESC=

      (SID_NAME=dg4odbc3)

      (ORACLE_HOME=oracle_home_directory)

      (PROGRAM=dg4odbc)

   )

)

where, oracle_home_directory is the directory where the gateway resides.

11.6.3 Multiple ODBC Data Sources Example: Stopping and Starting the Oracle Net Listener

Perform the following steps:

1. From the Start menu, select Settings, Control Panel and then select Services.
2. Select the Oracle Net Listener service for the gateway.
3. Click Stop.
4. Click Start.

11.6.4 Multiple ODBC Data Sources Example: Configuring Oracle Database for Gateway Access

Add two connect descriptor entries to the tnsnames.ora file. You must have an entry for each gateway instance, even if the gateway instances access the same database.

The following example shows the entry for the original installed gateway first, followed by the two entries for the new gateway instances:

old_dsn_using=(DESCRIPTION=

              (ADDRESS=

                (PROTOCOL=TCP)

                (PORT=port_number)

                (HOST=host_name))

                (CONNECT_DATA=

                    (SID=dg4odbc))

               (HS=OK))

new_dsn2_using=(DESCRIPTION=

              (ADDRESS=

                (PROTOCOL=TCP)

                (PORT=port_number)

                (HOST=host_name))

                (CONNECT_DATA=

                    (SID=dg4odbc2))

                (HS=OK))

new_dsn3_using=(DESCRIPTION=

              (ADDRESS=

                (PROTOCOL=TCP)

                (PORT=port_number)

                (HOST=host_name))

                (CONNECT_DATA=

                    (SID=dg4odbc3))

                (HS=OK))

The value for PORT is the TCP/IP port number of the Oracle Net Listener that is listening for the gateway. The number can be found in the listener.ora file used by the Oracle Net Listener. The value for HOST is the name of the machine on which the gateway is running. The name also can be found in the listener.ora file used by the Oracle Net Listener.

11.6.5 Multiple ODBC Data Sources Example: Accessing ODBC Data

Enter the following to create a database link for the dg4odbc2 gateway:

SQL> CREATE PUBLIC DATABASE LINK ODBC2 CONNECT TO

  2  "user2" IDENTIFIED BY "password2" USING 'new_dsn2_using';

Enter the following to create a database link for the dg4odbc3 gateway:

SQL> CREATE PUBLIC DATABASE LINK ODBC3 CONNECT TO

  2  "user3" IDENTIFIED BY "password3" USING 'new_dsn3_using';

After the database links are created, you can verify the connection to the new ODBC data sources, as in the following:

SQL> SELECT * FROM ALL_USERS@ODBC2;

SQL> SELECT * FROM ALL_USERS@ODBC3;