14 Configuring Oracle Database Gateway for DRDA

14.1.1 Choose a System Identifier for the Gateway

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 DRDA database you are accessing. However, if you want to access two DRDA databases, you need two gateway SIDs, one for each instance of the gateway. If you have one DRDA database and want to access it sometimes with one set of gateway parameter settings, and other times with different gateway parameter settings, you can do that by having multiple gateway SIDs for the single DRDA database. The SID is used as part of the file name for the initialization parameter file.

14.1.2 Customize the Initialization Parameter File

Tailor the parameter file with additional parameters as needed. Refer to Appendix C, "Initialization Parameters" for a list of supported initialization parameters. Also refer to Chapter 15, "Security Considerations" for security aspects to tailoring the parameter file.

14.2.1 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/dg4db2/admin directory where $ORACLE_HOME is the directory under which the gateway is installed.

LISTENER=
        (ADDRESS= 
          (PROTOCOL=TCP)
          (HOST=host_name)
          (PORT=port_number))

SID_LIST_LISTENER=
   (SID_LIST=
      (SID_DESC= 
         (SID_NAME=gateway_sid)
         (ORACLE_HOME=oracle_home_directory)
         (PROGRAM=dg4db2)
      )
   )

SID_LIST_LISTENER=
(SID_LIST= 
   (SID_DESC=.
     .
   )
   (SID_DESC=.
     .
   )
   (SID_DESC=
      (SID_NAME=gateway_sid)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4db2)
   )
)

14.2.2 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. Set the PATH environment variable to $ORACLE_HOME/bin where $ORACLE_HOME is the directory in which the gateway is installed. If you have the Bourne or Korn Shell, enter the following:

   $ PATH=$ORACLE_HOME/bin:$PATH;export PATH
   $ LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH; export LD_LIBRARY_PATH
   

   If you have the C Shell, enter the following:

   $ setenv PATH $ORACLE_HOME/bin:$PATH
   $ setenv LD_LIBRARY_PATH $ORACLE_HOME/lib:$LD_LIBRARY_PATH
   

   Table 14-1 specifies which parameter value to use for the different platforms:

   Table 14-1 Parameter Values for UNIX Based Platforms

   Platform	Parameter Value
   Solaris (SPARC) 64 bit	LD_LIBRARY_PATH_64=$ORACLE_HOME/lib
   Linux x86, and Linux x86 64 bit	LD_LIBRARY_PATH=$ORACLE_HOME/lib
   AIX	LIBPATH=$ORACLE_HOME/lib

   
   

2. If the listener is already running, use the lsnrctl command to stop the listener and then start it with the new settings, as follows:

   $ lsnrctl stop
   $ lsnrctl start 
   

3. Check the status of the listener with the new settings, as follows:

   $ lsnrctl status
   

   The following is a partial output from a lsnrctl status check:

.
.
.
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=204.179.99.15)(PORT=1551)))
Services Summary...
Service "dg4db2" has 1 instance(s).
  Instance "dg4db2", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully

In this example, the service name is dg4db2, which is the default SID value assigned during installation.

14.5.1 Configuring tnsnames.ora

Edit the tnsnames.ora file to add a connect descriptor for the gateway. The following is the 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:

14.5.2 Configuring tnsnames.ora for Multiple Listeners

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.

14.7.1 Multiple DRDA Databases Example: Configuring the Gateway

Choose One System ID for Each DRDA Database

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

• dg4db22 for the gateway accessing database db2

• dg4db23 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/dg4db2/admin/initdg4db2.ora, twice, naming one with the gateway SID for db2 and the other with the gateway SID for db3:

$ cd $ORACLE_HOME/dg4db2/admin
$ cp initdg4db2.ora initdg4db22.ora
$ cp initdg4db2.ora initdg4db23.ora

14.7.2 Multiple DRDA Databases 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=dg4db2)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4db2)
   )
   (SID_DESC=
      (SID_NAME=dg4db22)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4db2)
   )
   (SID_DESC=
      (SID_NAME=dg4db23)
      (ORACLE_HOME=oracle_home_directory)
      (PROGRAM=dg4db2)
   )
)

where, oracle_home_directory is the directory where the gateway resides.

14.7.3 Multiple DRDA Databases Example: Stopping and Starting the Oracle Net Listener

If the listener is already running, use the lsnrctl command to stop the listener and then start it with the new settings, as follows:

$ lsnrctl stop
$ lsnrctl start

14.7.4 Multiple Databases Example: Configuring Oracle Database for Gateway Access

old_db_using=(DESCRIPTION=
              (ADDRESS=
                (PROTOCOL=TCP)
                (PORT=port_number)
                (HOST=host_name))
                (CONNECT_DATA=
                    (SID=dg4db2))
               (HS=OK))
new_db2_using=(DESCRIPTION=
              (ADDRESS=
                (PROTOCOL=TCP)
                (PORT=port_number)
                (HOST=host_name))
                (CONNECT_DATA=
                    (SID=dg4db22))
                (HS=OK))
new_db3_using=(DESCRIPTION=
              (ADDRESS=
                (PROTOCOL=TCP)
                (PORT=port_number)
                (HOST=host_name))
                (CONNECT_DATA=
                    (SID=dg4db23))
                (HS=OK)) 

14.7.5 Multiple DRDA Databases Example: Accessing DB2 Data

Enter the following to create a database link for the dg4db22 gateway:

SQL> CREATE PUBLIC DATABASE LINK DRDA2 CONNECT TO
  2  "user2" IDENTIFIED BY "password2" USING 'new_db2_using';

Enter the following to create a database link for the dg4db23 gateway:

SQL> CREATE PUBLIC DATABASE LINK DRDA3 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 DRDA databases, as in the following:

SQL> SELECT * FROM ALL_USERS@DRDA2;

SQL> SELECT * FROM ALL_USERS@DRDA3;