2 Release Information

2.6.1 DB2 Considerations

The following considertaions are exist in the 10g release:

DD Basic Tables and Views

The owner of DD basic tables and views is OTGDB2. This cannot be changed.

SUBSTR Function Post-Processed

The SUBSTR function can be used with the Oracle Database in ways that are not compatible with a DRDA Server database, such as DB2/OS390. Therefore, the SUBSTR function is post-processed. However, it is possible to allow the server to process it natively using the "Native Semantics" feature. Refer to Chapter 13, "Developing Applications", for details.

AVS Mapping User IDs (DB2/VM)

APPC VTAM Support (AVS) has problems mapping user IDs that are sent using lowercase letters or special characters. Contact your IBM representative for additional information about this problem.

Support for DRDA Server Character Sets

Support for character sets used by a DRDA Server is configurable through the gateways Codepage Map Facility. Refer to Appendix D, "National Language Support", for more information.

Data type Limitations

Refer to "DRDA Data type to Oracle Data type Conversion" for detailed information about data types. 

SAVEPOINT Command Is Not Supported

Oracle Transparent Gateway for DRDA does not support the SQL SAVEPOINT.

Null Values and Stored Procedures

Null values are not passed into, or returned from, calls to stored procedures through the gateway.

String Concatenation of Numbers

String concatenation of numbers is not allowed in DB2/400, DB2/UDB, and DB2/OS390. For example, 2||2 is not allowed.

GLOBAL_NAMES Initialization Parameter

If GLOBAL_NAMES is set to TRUE in the Oracle Database INIT.ORA file, then in order to be able to connect to the gateway, you must specify the Heterogeneous Services (HS) initialization parameter, HS_DB_DOMAIN, in the Gateway Initialization Parameter file to match the value of the DB_DOMAIN parameter of the Oracle Database. Refer to Chapter 11, "Configuring the Gateway", for more information.

Binding the DRDA Package on DB2/UDB

The DRDA gateway package must be bound on the DRDA Server before the gateway can perform any SQL operations. Because of a DB2/UDB restriction, the ORACLE2PC table must be created in the DB2/UDB database before the package can be bound. For details, refer to Chapter 11, "Configuring the Gateway".

Date Arithmetic

In general, the following types of SQL expression forms do not work correctly with the gateway because of DRDA Serve limitations:

date + number
number + date
date - number
date1 - date2

DRDA Server does not allow number addition or subtraction with date data types. The date and number addition and subtraction (date + number, number + date, date - number) forms are sent through to the DRDA Server where they are rejected.

Also, DRDA Server does not perform date subtraction consistently. When you subtract two dates (date1 - date2), differing interpretations of date subtraction in the DRDA Server cause the results to vary by server.

Row Length Limitation

Because of a restriction of the DRDA architecture, rows with aggregate length exceeding 32KB in DRDA representation cannot be stored or retrieved.

LONG Data type in SQL*Plus

SQL*Plus cannot fetch LONG columns from the Oracle Transparent Gateway for DRDA.

Dictionary Views Are Not Provided for DB2/VM

Currently the Oracle Transparent Gateway for DRDA provides SQL for defining DB2/OS390, DB2/400, and DB2/UDB views that emulate parts of the Oracle Database dictionary. These are required for certain applications and tools that query dictionary tables. View definitions for DB2/VM are not provided in this release.

Single Gateway Instance per DRDA Network Interface

When installing the gateway, a proper DRDA Network Interface must be chosen. Only one DRDA Network Interface may be chosen and installed per gateway instance. If the gateway product is reinstalled, and if a Network Interface different from the previous installation is chosen, then the new choice will overlay the current installation. Reconfiguration of the Gateway Initialization Parameters must occur at this point in order to ensure proper gateway operation. If you wish to have both SNA and TCP/IP DRDA Network Interfaces installed, then you must install two separate gateway homes.

Stored Procedures and Transaction Integrity

IBM DB2 has introduced a feature called Commit on Return for stored procedures. This feature allows DB2 to perform an automatic commit after a stored procedure runs successfully. This feature is enabled when the procedure is created. To ensure data integrity, this feature is not supported by the Oracle Transparent gateway for DRDA in a heterogeneous environment. When attempting to call a stored procedure which has this feature enabled, through the gateway, the gateway will return an error, ORA-28526 or PLS-00201 (identifier must be declared).

2.6.2 SQL Limitations

The SQL limitations are descibed as follows:

Oracle ROWID Column

The DB2 ROWID column is not compatible with the Oracle ROWID column. Because the ROWID column is not supported, the following restrictions apply:

• UPDATE and DELETE are not supported with the WHERE CURRENT OF CURSOR clause. To update or delete a specific row through the gateway, a condition style WHERE clause must be used. (Bug No. 205538)

  When UPDATE and DELETE statements are used in precompiler and PL/SQL programs, they rely internally on the Oracle ROWID function.

• Snapshots between Oracle Database and DB2 are not supported.

  Snapshots rely internally on the Oracle ROWID column.

Oracle Bind Variables

Oracle bind variables become SQL parameter markers when used with the gateway. Therefore, the bind variables are subject to the same restrictions as SQL parameter markers.

For example, the following statements are not allowed:

WHERE :x IS NULL 
WHERE :x = :y 

CONNECT BY Is Not Supported

Oracle Transparent gateway for DRDA does not support CONNECT BY in SELECT statements.

COUNT Function Compatibility

The following DRDA servers do not support all forms of the COUNT function, specifically COUNT(colname) and COUNT(ALL colname):

DB2 OS/390 V6,

DB2/VM V6 and V7

The default for all DRDA server platforms, except DB2/VM, is for all forms of COUNT to be passed to the DRDA server as it is. For DB2/VM, the forms COUNT(colname) and COUNT(ALL colname) have been disabled by default and will be post-processed.

If the gateway is to be used with one of the releases of DRDA servers, then it may be necessary to disable the default usage of this form of COUNT.

Refer to Chapter 13, "Mapping the COUNT Function" and Chapter 13, "Native Semantics" for details on how to disable or enable compatibility for these forms of COUNT.