Activation when the IMS catalog is shared

IMS automatically coordinates resource changes globally among IMS systems that share IMS-managed ACBs. Internally, IMS uses a global coordination process that is similar to the process that is used by the Global Online Change process to activate changes in an ACBLIB data set.

IMS determines which IMS systems are sharing ACBs in an IMS catalog by the specification of the ACBSHR= parameter in each system. Only those systems that specify ACBSHR=Y are included in the global coordination of resource activation. IMS systems that specify ACBSHR=N are not. The ACBSHR= parameter is specified either in the COMMON_SERVICE_LAYER section of the DFSDFxxx member or in the DFSCGxxx member of the PROCLIB data set.

One IMS system functions as master for the global coordination of resource activation in managed ACB environments. To function as a master, ACBSHR=Y must be specified in the IMS system. The master updates the IMS catalog directory data sets and notifies the other IMS systems in the IMSplex that share the IMS catalog to refresh their resource definitions from the IMS directory. If resource activation is triggered by an IMPORT DEFN SOURCE(CATALOG), the master includes all IMS systems that specify ACBSHR=Y in the global coordination of the resource activation even if the command is not explicitly routed to those systems.

If one of the sharing IMS systems is down while resources are activated globally, IMS takes note of the system that is down. If the IMS system comes up while the resources are still being activated, the restarting IMS system issues message DFS4373I and waits for the processing to complete before it continues. If the IMS system comes back up after the processing of the command is complete, the IMS system issues a message to indicate that the IMS catalog was updated while the IMS system was down. If the IMS system is restarting with a warm or emergency restart, the IMS system refreshes the ACBs from the IMS catalog.

Staging the activation of modified PSBs in a managed-ACB environment.

If you are changing PSBs only, you can stage the activation of the modified PSBs across an IMSplex by using the IMPORT DEFN SOURCE(CATALOG) command with the OPTION(UPDATEPSB) keyword. Staging the activation of PSBs allows you to maintain availability by activating and testing the modified PSBs on one IMS system while continuing to process work with the original PSB on other IMS systems. If DBDs are in the staging data set of the IMS catalog when the OPTION(UPDATEPSB) keyword is specified, the IMPORT DEFN SOURCE(CATALOG) is rejected.

Error scenarios during the activation of resources in a data sharing environment

If the master abends during the activation of resources, the other IMS systems in the data sharing group attempt to take over activation processing and clean up locally.

Only one of the other IMS systems that share the IMS catalog can take over as the new master to back out or commit the updates to the directory data set of the IMS catalog. If the new master IMS also abends or cannot complete the take over process successfully, you must resubmit the IMPORT DEFN SOURCE(CATALOG) command or the DDL statements to clean up the directory data sets.

If an IMS system abends during import processing, you can determine the status of both the import processing and the take over attempt by issuing the QUERY MEMBER TYPE(IMS) SHOW(STATUS) command.