IMS management of ACBs

IMS can manage the runtime application control blocks (ACBs) for databases and program views for you. You can define databases and program views by using SQL DDL statements or by using the IMS generation utilities.

ACBs are the runtime blocks that represent the active databases and program views in online and batch IMS environments. They are created from the databases and program views that you define to the IMS system.

Most ACBs are pre-built, stored in a data set in binary format, and loaded into memory by the online IMS system or by batch application programs. Some application programs and some utilities, such as those that run in an offline DL/I batch region, build ACBs dynamically during run time.

When IMS manages ACBs, as indicated by ACBMGMT=CATALOG in the <CATALOG> section of the DFSDFxxx member, IMS stores ACBs in the IMS directory, a collection of system-managed data sets that are associated with an IMS catalog. The IMS directory data sets include data sets for the active ACBs, a staging data set for ACBs that are pending activation, and a boot strap data set that IMS uses to manage the IMS directory.

When IMS managed ACBs, IMS can build, activate, and load ACBs into memory dynamically when database and program view definitions are submitted to IMS by using SQL DDL statements. Upon receiving the SQL statements, IMS automatically updates the IMS catalog and can, if directed to do so, activate certain changes to database or program view definitions automatically.

Changes that are not activated automatically or that are saved in the staging data set for later activation, can be activated by issuing the IMS type-2 IMPORT DEFN SOURCE(CATALOG) command. IMS type-2 command support requires the Operations Manager (OM) and Structured Call Interface (SCI) components of the IMS Common Service Layer (CSL). In data sharing environments, the CSL Resource Manager (RM) component is also required.

Defining databases and program views with SQL DDL statements is an alternative to the process of coding DBD and PSB source, generating DBDs, PSBs, and ACBs with utilities, and performing an Online Change process to activate the resulting ACBs. The DDL statements can be submitted to IMS through a separate product, such as the IMS Enterprise Suite Explorer for Development.

When IMS manages ACBs, you can also still define databases and program views by using the DBD and PSB generation utilities and build ACBs by using either the ACB Maintenance utility or the ACB Generation and Catalog Populate utility (DFS3UACB).

If you use the DFS3UACB utility, in addition to building the ACBs, the utility can also update the IMS catalog and activate the ACBs by loading them into the IMS directory. If you do not use the DFS3UACB utility, you can achieve the same results by using the ACB Maintenance utility and the IMS Catalog Populate utility (DFS3PU00).

The IMS Catalog Directory Recovery utility (DFS3RU00) can also be used to rebuild the IMS directory and write the online resources into the IMS directory data sets.

Both the DFS3UACB and the DFS3PU00 utilities require exclusive access when they update the IMS directory directly. So, if the utilities are run in the UPDATE mode, the IMS systems that use the IMS catalog that is being updated must be shut down. To avoid shutting down the IMS systems, run the utilities in STAGE mode and add them to the IMS directory by using the IMPORT DEFN SOURCE(CATALOG) command.

In many cases, whether you use DDL or the generation utilities, new or changed ACBs are placed in the staging data set as pending changes and you must activate the ACBs by issuing the IMPORT DEFN SOURCE(CATALOG) command. The Online Change process is not used. In other cases, such as when you delete a resource, the changes to the ACBs are activated automatically.

When you enable IMS management of ACBs, IMS performance is similar to what it is when an ACB library is used. IMS uses the same amount of I/O to access IMS-managed ACBs as it does to access ACBs in an ACB library.

Before IMS can manage ACBs, IMS and the IMS catalog must be set up to support ACB management by running the DFS3PU00 utility with the MANAGEDACBS=SETUP control statement that you provide as input. After IMS is set up for ACB management, you specify ACBMGMT=CATALOG in the <CATALOG> section of the DFSDFxxx PROCLIB member.

Restrictions

The following restrictions currently apply to the IMS management of ACBs function.

Change coordination restrictions with the IMS management of ACBs
In data sharing environments, if ACBSHR=Y is specified, the activation of resource changes in IMS systems that share an IMS catalog is always coordinated globally by the IMPORT DEFN SOURCE(CATALOG) command. Activating resources locally or separately in the individual IMS systems that share the IMS catalog is not supported. If you require more control over the activation of resource changes in IMS systems that share ACBs, use a separate aliased IMS catalog to manage the ACBs for each IMS system.
Database utilities and region type restrictions
Some IMS database-related utilities, and some vendor products that use the UDR or ULU region type, might still require access to DBDLIB and PSBLIB data sets even when the IMS managed ACBs function is enabled.
The following IMS utilities still require the use of DBDLIB or PSBLIB data sets:
  • DEDB Area Data Set Compare utility (DBFUMMH0)
  • DEDB Area Data Set Create utility (DBFUMRI0)
  • DEDB Sequential Dependent Delete utility (DBFUMDL0)
  • DEDB Sequential Dependent Scan utility (DBFUMSC0)
  • Database Surveyor utility (DFSPRSUR)
  • HALDB Index/ILDS Rebuild utility (DFSPREC0)
  • High-Speed DEDB Direct Reorganization utility (DBFUHDR0)
  • Partial Database Reorganization utility (DFSPRCT1 and DFSPRCT2)
  • Utility Control Facility (DFSUCF00)
IMS catalog population restrictions
If IMS manages ACBs, you must shut down IMS when you run one of the following utilities with the SETUP or the UPDATE parameter specified on the MANAGEDACBS= control statement:
  • The IMS Catalog Populate utility (DFS3PU00)
  • The ACB Generation and Catalog Populate utility (DFS3UACB)
However, you can run the DFS3PU00 utility with MANAGEDACBS=STAGE specified without shutting down IMS, even if IMS manages ACBs.
XRF does not support the IMS management of ACBs
The Extended Recovery Facility (XRF) function does not support the IMS management of ACBs.