When to Migrate
You can perform most migration activities during regular working hours. Obviously, identifying, punching or decompiling components, and adding or modifying source definitions of components will not disturb programs or systems that are currently executing.
Perform Some Tasks After System Shutdown
Depending on the specifics of the migration, you may not have to do any of it after regular working hours. To be on the safe side, however, you should plan to migrate or recompile load modules during off-peak hours. You must also perform any restructuring operations on the production database while no application access is taking place. Note that if it is an SQL-defined database, the restructuring occurs immediately as part of the execution of the DDL statement that define the change. Therefore, you may want to delay execution of the DDL statements until a time when the database is not being accessed by application programs.
Making Load Modules Available
If you migrate or recompile new copies of existing load modules while the system is down, they automatically come into use when you bring the system back up. If you migrate or recompile existing load modules while the system is up, you can control the time at which the new load modules take effect through the NEW COPY option of the SYSTEM system generation statement or DCMT VARY PROGRAM command.
NEW COPY Options
Using the NEW COPY option of the SYSTEM system generation statement, you can designate whether new load modules should be loaded automatically by the system or manually through explicit commands. If you choose to control loading manually, issue the DCMT VARY PROGRAM command with the NEW COPY option.
If you are migrating a new system whose tasks and programs are not enabled in the system generation, then you can migrate or recompile all of its load modules at any time. Access to the load modules will not be possible until the tasks and programs are enabled.
Check Your Work
When you have completed the mechanical migration of components, run a series of reports or issue a series of DISPLAY statements to check your work. However, to verify that the migration is complete and successful, you must test the new components in their new environment.
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