Global online change

The global online change function changes resources online for all IMS systems in an IMSplex.

The benefits of global online change are as follows:

Simplified process for changing resources online by issuing one instance of a command for online change for all IMS systems in the IMSplex
Continuous processing so that each IMS is not stopped and manually coordinated with online changes.
No situations where online change is committed on some IMS systems in the IMSplex and not committed on other IMS systems

With global online change, the master IMS control region coordinates online change of the following resources among all the IMS systems in the IMSplex:

Databases (DMB in ACBLIB)
Database directories (DDIR in MODBLKS)
MFS formats (FMTLIB)
Programs (PSB in ACBLIB)
Program directories (PDIR in MODBLKS)
Transactions (SMBs in MODBLKS)
Routing codes (RCTEs in MODBLKS)

Restriction: The online change function is not supported for the following types of resources when dynamic definition of the resources is enabled:

Database (DBD) and program view (PSB) resources when the IMS management of ACBs is enabled.
MODBLKS resources when dynamic resource definition is enabled.

Global online change operates through a master IMS control region, as specified by the user or by OM. OM uses RM, if RM is active, to coordinate the phases of online change with the other IMS systems in the IMSplex. Start online change by issuing the command INITIATE OLC through the OM API. At that time you can specify the master IMS control region. If you do not choose a master IMS control region, OM selects one of the IMS systems as the master IMS control region.

If global online change is specified in the IMSplex, the following components are required:

An IMSplex defined with CSL and at least one OM
CQS, if there is a resource structure in the IMSplex
The resource structure is used to save IMSplex-wide process status. It also provides more recovery capability during the online change, should any failures occur.
OLCSTAT data set, which must be initialized by the Global Online Change utility (DFSUOLC0) before the first IMS cold start
If you exclude RM from the IMSplex by specifying RMENV=N, each IMS system must have its own OLCSTAT data set and that OLCSTAT data set must contain the IMSID of the IMS system that owns it and no other IMSIDs.
OLC=GLOBAL and OLCSTAT= parameters in the DFSCGxxx PROCLIB member data set
CSLG= parameter in the IMS EXEC statement

At least one RM and a resource structure are recommended for global online change, but they are not required. Consider the following if you choose not to use RM or a resource structure. If you do not use an RM in your IMSplex, the OLCSTAT data set can contain only the IMSID of the IMS system that owns that OLCSTAT data set. Any attempt to restart an IMS system that contains an OLCSTAT data set with a different or multiple IMSIDs results in an abend. IMS rejects INITIATE OLC and TERMINATE OLC commands that are issued by an IMS system other than the IMS system that owns the OLCSTAT data set.

If you choose not to enable global online change, the MODSTAT data sets in the IMS procedure are optional. The IMS control region sample JCL includes DD statements for the MODSTAT data set and the MODSTAT2 data set (if XRF). If you specify the MODSTAT DD statements for an IMSplex where global online change is enabled, the MODSTAT and MODSTAT2 (if XRF) data sets must also exist.