IT Management

When it’s time to migrate your DB2 subsystems to Version 8 (V8), you’ll need to understand the significant differences for V8 migration from your previous DB2 migration strategies. The biggest difference is the introduction of three distinct DB2 operating modes that dictate the functionality you’ll have available.

However, before we discuss these modes, let’s quickly examine DB2 version migration basics. Typically, before you begin using a new version of DB2, you’ll migrate your test subsystems to the new version. Over time and after successful testing, you’ll migrate your production subsystems. When a subsystem is running on the new release (whether test or production), all the functionality of the new version is available to all DB2 users. For fallback purposes, many shops try to discourage immediate use of new functionality, preferring to ensure the new release is stable. But, prior to V8, there was no mechanism to support such a phased roll-in of new functionality.

You can exploit the three modes of DB2—compatibility mode (CM), enabling new function mode (ENFM), and new functionality mode (NFM)—to help manage how new functionality is used as you migrate to V8. As you begin the migration process, V8 will begin in CM. No new functionality is available at this stage. A V8 subsystem in CM is ideal for verifying functionality of existing applications and processes to ensure they function as they did in Version 7. Once this verification is complete, there’s no need to remain in CM.

The next phase moves V8 into ENFM. Job DSNTIJNE is run to begin enabling new functionality. At this stage, conversion of critical subsystem components has begun, but while in this mode, most new functionality isn’t available to users. Certain DB2 system catalog changes occur during this mode, including:

  • Movement of several (not all) tablespaces to Unicode
  • Extension of many existing columns to support long names
  • Alteration of certain catalog indexes to be NOT PADDED (because VARCHAR is used for long name columns).

Remember, too, that fallback to CM or to V7 isn’t permitted once you’ve entered ENFM.

You can remain in ENFM for as long as necessary to complete the task. IBM supplies the DSNTIJNH job that can be run to halt the enabling new function job. In this way, you can stage enabling new functionality mode over time. To pick up where you left off, run the DSNTIJNE job again. It will determine where it was halted and start running again. This feature permits phased implementation of the required changes, which is nice if you have only a limited window where you can make changes to the DB2 catalog.

The final stage of migrating to V8 is NFM. Job DSNTIJNF is run to move into NFM. When your subsystem is moved into this mode, all the new V8 functionality is available and you’ve successfully migrated to V8. In NFM, all the necessary DB2 system catalog changes are complete, including the addition of new tables and columns and any needed modification of existing columns. Additionally, several tablespaces will have grown to be too large for 4K pages, causing the DB2 catalog to require 8K, 16K, and 32K page sizes and buffer pools for the first time.

Remember these rules as you migrate to V8, moving from CM to ENFM and NFM:

  • You must be at V7 to migrate to V8; there’s no migration to V8 from any previous version.
  • You’ll need to apply the proper level of maintenance to V7 before migrating to V8 so you can fall back to V7 from CM. If you haven’t applied the fallback SPE, your V8 migration will fail and you’ll have to start over. This involves first applying the fallback SPE to V7, then proceeding with your migration.
  • Although you can’t fall back to V7 after you move to NFM, you can fall back to ENFM, if necessary. This can be useful to curtail usage of V8 functionality if it causes problems.
  • The migration process will change any user-defined indexes you’ve built on your DB2 catalog tables, but these indexes won’t be changed to NOT PADDED. If these indexes contain any column that refers to a long name, then your indexes will become quite large until you alter them to be NOT PADDED.
  • Be sure to migrate any existing Type 1 indexes to Type 2. V8 will fail if any Type 1 indexes are found in the catalog.

Summary

The migration process for V8 is quite different from any previous DB2 release migration. Be sure to study the DB2 manuals to understand all the nuances of each mode before beginning your subsystems migration to V8. Z