Modifying system resources online

IMS supports two separate functions that support modifying IMS resources online: dynamic resource definition (DRD) and the online change function. Authorized system operators and database administrators (DBAs) can change various system resources using IMS commands.

Dynamic resource definition

With DRD, you can perform the following actions on IMS system resources:

Use commands to create, update, and delete MODBLKS and MSC resources dynamically.
Use the enhanced Destination Creation exit routine (DFSINSX0), formerly called the Output Creation exit routine, to create transactions (and, if necessary, the programs that are associated with the transactions) instead of using the online change process.
Use the Program Creation user exit routine (PGMCREAT) to dynamically create the runtime program resourece for a program that is to be scheduled in a BMP or JBP dependent region.

DRD enables you to avoid the online change process for MODBLKS resources. To change resources other than MODBLKS and MSC resources online (for example, resources in IMS.ACBLIB), you still need to use the online change process.

DRD is enabled by specifying MODBLKS=DYN in the DFSDFxxx member or the DFSCGxxx member. To enable DRD for MSC resources, you must also specify MSCRSCS=DYN in the DFSDFxxx member.

When dynamic resource definition (DRD) is enabled in your IMS system, you can use the following type-2 commands to create, modify, and delete runtime resource and descriptor definitions for application programs, databases, routing codes and transactions.

CREATE
UPDATE
DELETE
IMPORT

The CREATE, UPDATE, DELETE, and IMPORT commands in a DRD-enabled system are essentially the same as adding, modifying, or deleting the system definition macros for IMS runtime resource definitions.

The EXPORT command is used to export MODBLKS runtime resource and descriptor definitions from the online IMS system to a resource definition data set (RDDS) or IMSRSC repository. The MODBLKS resource and descriptor definitions can then be added to IMS dynamically through the IMPORT command. For dynamically defined MSC resources, use the automatic export function to export the resources to the IMSRSC repository. The MSC resource definitions can then be added to IMS dynamically at IMS cold start by using the automatic import function.

By exporting runtime resource and descriptor definitions to a repository, you can create resources for another IMS in the IMSplex.

Modifications to IMS resources that are made by use of type-2 commands are recoverable across a warm or emergency restart. Runtime MODBLKS descriptor definitions and MSC definitions are lost when an IMS system is cold started unless you perform the following actions:

For runtime MODBLKS descriptor definitions, export MODBLKS resource and descriptor definitions to the RDDS or repository while IMS is running. MODBLKS resource and descriptor definitions can be exported either explicitly by use of the EXPORT DEFN command, or automatically if AUTOEXPORT is enabled in the DFSDFxxx PROCLIB member.
For MSC definitions, use the automatic export function to export the definitions to the IMSRSC repository.

If you want to modify resources, use the QUERY command to view the resource information before making the change.

You must ensure that:

Commands are routed to and executed on the systems where you want the changes to be applied.
Any changes made dynamically with the DRD commands are recovered across a cold start. Here are some examples of possible methods:
- Using automatic export to export updated resource definitions to an RDDS or the IMSRSC repository, and then using automatic import during IMS cold start to retrieve the definitions from the RDDS or the IMSRSC repository.
- Issuing the EXPORT DEFN TARGET(REPO) command while IMS is running and then using automatic import from the repository.
  You can periodically issue the EXPORT DEFN TARGET(REPO) OPTION(CHANGESONLY) command to write changes to the repository.

The following IMS resources and resource descriptors can be defined dynamically:

Application programs
Databases
Fast Path routing codes
Transactions
MSC resources, including logical links, physical links, logical link paths (MSNAMEs), and remote logical terminals (LTERMs)

You can enter the CREATE, UPDATE, DELETE, and MODIFY type-2 commands directly through:

TSO SPOC
Batch SPOC
REXX automation (through the REXX SPOC API)
Your own programs that use the OM API

Similarly, you can use the Manage Resource panels to enter DRD commands by selecting an option from the IMS Application Menu. The Manage Resource panels are a hierarchy of ISPF panels that offer an alternative way to enter commands. From the Manage Resource panels, you can:

Define and control IMS resources
Select an action that you want to perform (for example, CREATE)
Manage attributes of a resource

Figure 1. Example of a Manage Resource panel

---------------------------------------------------------------------------------
                                                                                  MORE: +
 * NAME   Transaction name . . 4NEWTRAN                                     
 SET                                                                        
   AOCMD    AOI command option . . . . . . . N          CMD, N, Tran, Y     
   CLASS    Class. . . . . . . . . . . . . . 1          1-999               
   CMTMODE  Commit mode. . . . . . . . . . . SNGL       Sngl, Mult          
   CONV     Conversational . . . . . . . . . N          Y, N                
   DCLWA    Log write-ahead option . . . . . Y          Y, N                
   DIRROUTE MSC direct routing option. . . . N          Y, N                
   EDITRTN  Input edit routine . . . . . . .                                
   EDITUC   Edit to uppercase. . . . . . . . Y          Y, N                
   EMHBSZ   EMH buffer size. . . . . . . . .            12-30720 
----------------------------------------------------------------------------------

You can use many IMS commands to perform similar control functions for different types of resources.

Online change function

There are two variations of online change:

Local online change, which enables you to make online changes to IMS resources for one IMS.
Global online change, which enables you to coordinate online changes to IMS resources across all IMS systems in an IMSplex.

Global online change is not supported in all IMS environments that support local online change. Environments that require the MODSTAT/MODSTAT2 data sets do not support global online change. FDBR, XRF alternate, and DBCTL-standby do not participate in global online process, however they keep track of the online change from the log records.

Table 1. IMS environments that support online change
Environment	Supports local online change?	Supports global online change?
DB/DC	Yes	Yes
DBCTL	Yes	Yes
DBCTL-standby	No	No
DCCTL	Yes	Yes
FDBR	No	No
XRF active	Yes	Yes
XRF alternate	No	No