Sharing an IMS catalog

As an IMS HALDB database, the IMS catalog can be shared among multiple IMS systems in a data sharing environment.

When the IMS management of ACBs is enabled, sharing an IMS catalog greatly simplifies the coordination of changes to shared databases and program views across all of the IMS systems that use those resources. After the changes are submitted to IMS, either via DDL statements or via one of the IMS catalog population utilities, the changes are activated in the online IMS systems either automatically or by issuing the IMPORT DEFN SOURCE(CATALOG) command. If the IMS catalog is not shared, the changes need to be applied to each sharing IMS system independently and IMS does not coordinate the activation of the changed resources across the data sharing group.

To share an IMS catalog, you must configure your data sharing environment as you would for any shared IMS database.

You can share the IMS catalog and directory data sets with a DCCTL system in a sysplex environment so that the DCCTL system can use the IMS management of ACBs enhancement. To enable IMS management of ACBs in a DCCTL system, specify ACBMGMT=CATALOG in the CATALOG or CATALOGxxxx section of the DFSDFxxx member of the DCCTL IMS instance.

The IMS catalog and directory must be created and maintained by a non-DCCTL IMS in the sysplex. The DCCTL system cannot create or maintain the IMS catalog or the directory data sets.

Additionally, sharing an IMS catalog requires the following specific actions.

Configure the IMS catalog to use DBRC.
DBRC is required for data sharing of the IMS catalog by application programs and utilities that are running in either online IMS dependent regions or in batch regions.
Register the IMS catalog database in the RECON data set with a share level of 2 or 3.
You can specify the share level either by using the DBRC commands INIT.DB or CHANGE.DB or by using the TSO HALDB Partition Definition utility (%DFSHALDB). The share level applies to the HALDB master database and all of the partitions that it contains.
For recovery purposes, register the IMS catalog database data sets as members of a new or existing change accumulation group in DBRC, as described in Change accumulation groups.
Specify a SHAREOPTIONS value of (1,3), (2,3), or (3,3) when you define the VSAM data sets of the IMS catalog.
The primary index, secondary index, and indirect list data set (ILDS) of the IMS catalog use VSAM.
If application programs or utilities in multiple IMS systems must update a shared IMS catalog concurrently, change the access of the IMS catalog to update by using one of the following commands:
- UPDATE DB NAME(DFSCD000,DFSCX000) START(ACCESS) SET(ACCTYPE=UPD)
- START DB DFSCD000 DFSCX000 ACCESS=UP
Enable IRLM support in the JCL of the application programs and utilities that access the shared IMS catalog by specifying Y and the IRLM ID in the execution parameters.
For example, the second Y and irlmid values in following execution parameters for the IMS Catalog Populate utility (DFS3PU00) specify IRLM support:
```
PARM=(DLI,DFS3PU00,DFSCP001,,,,,,,,,,,Y,Y,irlmid,,,,,,,,,,,'DFSDF=001')
```