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 SQL Server database you are accessing. The SID is used as part of the file name for the initialization parameter file. The default SID is dg4msql.

You can define a gateway SID, but using the default of dg4msql is easier because you do not need to change the initialization parameter file name. However, if you want to access two SQL Server databases, you need two gateway SIDs, one for each instance of the gateway. If you have only one SQL Server database and 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 SQL Server database.

The initialization parameter file must be available when the gateway is started. During installation, the following default initialization parameter file is created:

ORACLE_HOME\dg4msql\admin\initdg4msql.ora

Where ORACLE_HOME is the directory under which the gateway is installed.

This initialization file is for the default gateway SID. If you are not using dg4msql as the gateway SID, you must rename the initialization parameter file using the SID you chose in the preceding step Choose a System Identifier for the Gateway. This default initialization parameter file is sufficient for starting the gateway, verifying a successful installation, and running the demonstration scripts.

A number of initialization parameters can be used to modify the gateway behavior. Refer to Initialization Parameters for the complete list of initialization parameters that can be set. Changes made to the initialization parameters only take effect in the next gateway session. The most important parameter is the HS_FDS_CONNECT_INFO which describes the connection to the non-Oracle system.

The default initialization parameter file already has an entry for this parameter. The syntax for HS_FDS_CONNECT_INFO is as follows:

HS_FDS_CONNECT_INFO= host_name/[instance_name][/database_name]

Where:

Both instance_name and database_name are optional. If instance_name is omitted and database_name is provided, the slash (/) is required. This can be shown as follows:

HS_FDS_CONNECT_INFO= host_name//database_name

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\dg4msql\admin directory where ORACLE_HOME is the directory under which the gateway is installed.

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

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:

To ensure higher availability, you can specify multiple listeners within the connect descriptor.

 connect_descriptor=
    (DESCRIPTION=
       (ADDRESS=
          (PROTOCOL=TCP)
          (HOST=host_name_1)
          (PORT=port_number_1)
       )
       (ADDRESS=
          (PROTOCOL=TCP)
          (HOST=host_name_2)
          (PORT=port_number_2)
       )
       (CONNECT_DATA=
          (SID=gateway_sid))
       (HS=OK))

This indicates that, if the listener for host_name_1 and port_number_1 is not available, then the second listener for host_name_2 and port_number_2 will take over.

For the gateway to recover distributed transactions, a recovery account and password must be set up in the SQL Server database. By default, both the user name of the account and the password are RECOVER. The name of the account can be changed with the gateway initialization parameter HS_FDS_RECOVERY_ACCOUNT. The account password can be changed with the gateway initialization parameter HS_FDS_RECOVERY_PWD.

When configuring the gateway for two-phase commit, a table must be created in the SQL Server database for logging transactions. The gateway uses the transaction log table to check the status of failed transactions that were started at the SQL Server database by the gateway and registered in the table.

The table, called HS_TRANSACTION_LOG, consists of two columns, GLOBAL_TRAN_ID, data type CHAR(64) NOT NULL and TRAN_COMMENT, data type CHAR(255).

You can use another name for the log table, other than HS_TRANSACTION_LOG, by specifying the other name using the HS_FDS_TRANSACTION_LOG initialization parameter.

Create the transaction log table in the user account you created in Create a Recovery Account and Password. Because the transaction log table is used to record the status of a gateway transaction, the table must reside at the database where the SQL Server update takes place. Also, the transaction log table must be created under the owner of the recovery account.

To create a transaction log table use the dg4msql_tx.sql script, located in the directory ORACLE_HOME\dg4msql\admin where ORACLE_HOME is the directory under which the gateway is installed. Use isql to execute the script at the MS-DOS prompt, as follows:

> isql -Urecovery_account -Precovery_account_password [-Sserver] -idg4msql_tx.sql

Choose One System ID for Each SQL Server Database

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

• dg4msql2 for the gateway accessing database db2

• dg4msql3 for the gateway accessing database db3

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\dg4msql\admin\initdg4msql.ora, twice, naming one with the gateway SID for db2 and the other with the gateway SID for db3:

> cd ORACLE_HOME\dg4msql\admin
> copy initdg4msql.ora initdg4msql2.ora
> copy initdg4msql.ora initdg4msql3.ora

Change the value of the HS_FDS_CONNECT_INFO parameter in the new files.

For initdg4msql2.ora, enter the following:

HS_FDS_CONNECT_INFO=204.179.79.15//db2

For initdg4msql3.ora, enter the following:

HS_FDS_CONNECT_INFO=204.179.79.15//db3

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=dg4msql)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4msql)
   )
   (SID_DESC=
      (SID_NAME=dg4msql2)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4msql)
   )
   (SID_DESC=
      (SID_NAME=dg4msql3)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4msql)
   )
)

where, oracle_home_directory is the directory where the gateway resides.

Perform the following steps:

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.

This example describes how to configure Oracle Net on the Oracle database for multiple gateway instances. It shows the entry for the original installed gateway first, followed by the two entries for the new gateway instances:

old_db_using=(DESCRIPTION=
              (ADDRESS=
                (PROTOCOL=TCP)
                (PORT=port_number)
                (HOST=host_name))
                (CONNECT_DATA=
                    (SID=dg4msql))
               (HS=OK))
new_db2_using=(DESCRIPTION=
              (ADDRESS=
                (PROTOCOL=TCP)
                (PORT=port_number)
                (HOST=host_name))
                (CONNECT_DATA=
                    (SID=dg4msql2))
                (HS=OK))
new_db3_using=(DESCRIPTION=
              (ADDRESS=
                (PROTOCOL=TCP)
                (PORT=port_number)
                (HOST=host_name))
                (CONNECT_DATA=
                    (SID=dg4msql3))
                (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.

Enter the following to create a database link for the dg4msql2 gateway:

SQL> CREATE PUBLIC DATABASE LINK MSQL2 CONNECT TO
  2  "user2" IDENTIFIED BY "password2" USING 'new_db2_using';

Enter the following to create a database link for the dg4msql3 gateway:

SQL> CREATE PUBLIC DATABASE LINK MSQL3 CONNECT TO
  2  "user3" IDENTIFIED BY "password3" USING 'new_db3_using';

After the database links are created, you can verify the connection to the new SQL Server databases, as in the following:

SQL> SELECT * FROM ALL_USERS@MSQL2;

SQL> SELECT * FROM ALL_USERS@MSQL3;