Overview of dynamic resource definition

With dynamic resource definition (DRD), you can use type-2 commands to define MODBLKS resources such as application programs, databases, routing codes, and transactions, and resource descriptors, and MSC resources such as definitions for MSC physical links, logical links, logical link paths, and remote logical terminals.

MODBLKS resources

For IMS systems in which DRD for MODBLKS resources is not enabled or is unavailable, you must use the APPLCTN, DATABASE, RTCODE, and TRANSACT macros, along with the batch system definition process, to create the resource definitions for these resources and store them in the IMS.MODBLKS data set. The following figure shows the control block generation process:
Figure 1. Control block generation process for MODBLKS resources
begin figure description. This figure is described in the surrounding text. end figure description.

With DRD enabled, the APPLCTN, DATABASE, RTCODE, and TRANSACT macros are optional. If you do not code these macros as part of the system definition process, you can either import resource definitions into IMS from a resource definition data set (RDDS) or an IMSRSC repository, or you can use type-2 commands to define resources to IMS dynamically (instead of using online change).

For IMS systems in which DRD is not enabled or unavailable, after IMS initialization, you use the online change process to add, change, and delete resource definitions dynamically. The online change process requires that you:

  1. Generate the resource definitions and store them in an IMS.MODBLKS staging library data set
  2. Run the Online Change Copy utility (DFSUOCU0) to copy the staging library into an inactive library
  3. Run a series of online change commands to cause the change to take effect (see the figure below)
Figure 2. Online change process for IMS resources
begin figure description. IMS.MODBLKS members are copied from a staging library (using the Online Change Copy utility) to an inactive library (IMS.MODBLKSA or IMS.MODBLKSB) and then commands are used to switch the inactive library with the active library. end figure description
Another aspect of the online change process is that, during the COMMIT phase, all the resources associated with the definitions in the IMS.MODBLKS data set are quiesced, which affects IMS availability.
Recommendation: Unless you have a simple system, and online change meets your requirements, use DRD with the repository or DRD with RDDSs rather than the IMS.MODBLKS data set.

To change some resources online (for example, resources in IMS.ACBLIB), you cannot use DRD and must use the online change process.

MSC resources

For IMS systems in which DRD for MSC resources is not enabled or is unavailable, you must use the MSPLINK, MSLINK, MSNAME, and NAME macros, along with the batch system definition process, to create the resource definitions for these resources, and store them in the IMS.DFSCLL3x and IMS.DFSCLL data sets. The following figure shows the control block generation process for MSC resources.

Figure 3. Control block generation process for MSC resources
begin figure description. This figure is described in the surrounding text. end figure description.
With DRD enabled for MSC resources, the MSPLINK, MSLINK, MSNAME, and NAME macros are optional. If you do not code these macros as part of the system definition process, you can import resource definitions into IMS from the IMSRSC repository, or you can use type-2 commands to define resources to IMS dynamically.
Tip: If dynamic definition of MSC resources is enabled, you can use the IMSRSC repository to save the dynamically created resource definitions permanently, even across cold starts.