GSAM databases and IMS management of ACBs

When the IMS management of ACBs is enabled, IMS stores the definitions for GSAM databases in the IMS catalog. The runtime control blocks are stored in the IMS directory, a system-managed extension of the IMS catalog that is generally equivalent to the ACB library (ACBLIB) in systems that use an ACBLIB.

In IMS systems that use ACBLIBs, the GSAM control blocks are not stored in the ACBLIB, but are instead loaded from the DBDLIB. Therefore, when you enable the IMS management of ACBs, you are not only relieved of having to manage both ACBLIB and DBDLIB data sets, but IMS stores and manages the GSAM definitions and control blocks for you, in essentially the same way that it does for other database types.

Each time a BMP application program that requires a GSAM database is scheduled in a dependent region, IMS loads the runtime control blocks for the GSAM database from the IMS catalog.

When the IMS management of ACBs is enabled for the first time by running the IMS Catalog Populate utility (DFS3PU00) with the MANAGEDACBS control statement, the utility creates DBD records in the IMS catalog for GSAM metadata and loads the GSAM control blocks into the system-managed data sets of the IMS catalog.

As a result, when IMS manages ACBs, the IMS catalog contains a DBD record for each GSAM database that was added by the IMS Catalog Populate utility. When the IMS management of ACBs is not enabled, the IMS catalog does not contain a DBD record for every GSAM database.