Migrating to a different release of DB2

When you are planning migration to a newer DB2® release, consider the following information:

To use the DB2 group attach facility with CICS®, CICS must be connected to DB2 Version 7 or later. You must also use DB2 Version 7 or later "early" (ERLY) code, meaning that the DB2 Version 7 or later version of db2hlq.SDSNLINK must be present in the MVS™ link list (where db2hlq is your chosen high-level qualifier for DB2 libraries). You must also apply APARS PQ44614, PQ45691, and PQ45692. (An MVS IPL is required for these DB2 APARS to take effect.)

With the group attach facility, instead of connecting to a specific DB2 subsystem, you can choose to connect to any one member of a data-sharing group of DB2 subsystems which is active on an MVS image. This allows you to use a common DB2CONN definition, specifying a group ID, across multiple cloned AORs, and to reconnect rapidly if the connection to DB2 fails. See Using the DB2 group attach facility for more information.

For the CICS DB2 attachment facility to use the open transaction environment (OTE), CICS must be connected to DB2 Version 6 or later. You must also use DB2 Version 6 or later "early" (ERLY) code, meaning that the DB2 Version 6 or later version of db2hlq.SDSNLINK must be present in the MVS link list. If you are using DB2 Version 6 early code, you must apply APARS PQ43242 and PQ50703. If you are using DB2 Version 7 early code, you must apply APARS PQ46501 and PQ50703. (An MVS IPL is required for these DB2 APARS to take effect.)

The open transaction environment enables the CICS DB2 task-related user exit to execute on an open TCB. Open TCBs, unlike the QR TCB or subtask thread TCBs, may be used for both non-CICS API requests (including requests to DB2) and threadsafe application code. Because threadsafe application code can be executed on the open TCB, a threadsafe CICS DB2 application should not need to switch between different TCBs several times during the execution of a CICS DB2 application. This situation produces a significant performance improvement where an application program issues multiple SQL calls. See Enabling CICS DB2 applications to exploit the open transaction environment (OTE) through threadsafe programming for more information on the open transaction environment and its performance benefits.

Start of changeIf you are migrating to DB2 Version 6 or later, note that with effect from DB2 Version 6, the CICS-DB2 language interface module, DSNCLI, is no longer shipped by the DB2 product. CICS ships the language interface stub in both the SDFHLOAD and SDFHAUTH libraries as a CICS named module, but also with appropriate aliases for compatibility. In SDFHLOAD, the stub is called DFHD2LI, with aliases of DSNCLI, DSNHLI, and DSNWLI. In SDFHAUTH, the stub is called DFHD2LIX, with aliases DSNCLI, DSNHLI, and DSNWLI. Start of changeEnsure that the library concatenation for the DB2 library SDSNLOAD and the CICS library SDFHLOAD are correct for your site, because both libraries contain the DSNHLI alias.End of changeEnd of change

If you are migrating to DB2 Version 6 or later, and using the open transaction environment, ensure that the limit set in your MAXOPENTCBS system initialization parameter is greater than the limit set in the TCBLIMIT attribute of your DB2CONN definition. In the open transaction environment, MAXOPENTCBS defines the total number of open TCBs allowed in the CICS system, and TCBLIMIT defines the number of these open TCBs that can be used to connect to DB2. If your MAXOPENTCBS limit is lower than your TCBLIMIT, a warning message is issued when CICS connects to DB2, and you may find that you do not have enough open TCBs available to process your DB2 workload. In addition, when running with Transaction Isolation active and connected to DB2 Version 6 or later, set MAXOPENTCBS to the value of max tasks (MXT) or higher. This will minimise the possibility of TCB stealing due to a TCB being allocated to the wrong subspace. For more information, see The MAXOPENTCBS system initialization parameter and TCBLIMIT.

Related concepts
Installation and migration notes for CICS DB2
CICS startup JCL requirements for connection to DB2
Supported releases of DB2
Migrating from a CICS release that used RCT definitions for CICS DB2 resources
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