Illustration of DBCTL startup parameter creation and selection

This illustration shows you how the DBCTL startup parameters are created and selected during startup.

If you are new to IMS system definition, use this figure while reading Generating DBCTL.

Note: OCU in Figure 1 refers to the IMS online change utility.
Figure 1. Creating and selecting DBCTL startup parameters
We can approach this figure from two perspectives, examining first, the items which are affected by the DBCTL startup parameters, and second, the different methods which can be used to create or select the parameters. The items which are affected by the DBCTL startup parameters are:In the library IMS.RESLIB, the IMS nucleus DFSVNUCx. The suffix 'x' on DFSVNUC can be specified by the DBCTL startup parameters, and it is the same as the suffix on the items listed below in IMS.MODBLKS and IMS.MATRIX.In the library IMS.MODBLKSm, the DDIR DFSDDIRx, and the PDIR DFSPDIRx. The suffix 'x' on the DDIR and PDIR can be specified by the DBCTL startup parameters, and is the same as the suffix on the IMS nucleus DFSVNUCx. The suffix 'm' on IMS.MODBLKS indicates the version of IMS.MODBLKS that is currently active, as indicated in the status data set IMS.MODSTAT, and it is the same as the suffix on IMS.MATRIX and IMS.ACBLIB.In the library IMS.MATRIXm, the Application Group Name (AGN) table DFSAGT0x. The suffix 'x' on DFSAGT0x can be specified by the DBCTL startup parameters, and is the same as the suffix on the IMS nucleus DFSVNUCx. The suffix 'm' on IMS.MATRIX indicates the version of IMS.MATRIX that is currently active, as indicated in IMS.MODSTAT, and it is the same as the suffix on IMS.MODBLKS and IMS.ACBLIB.In the library IMS.PROCLIB, members DFSVSMxx (which contains various parameters including those for VSAM), DFSFIXxx (page fixing), and DFSMPLxx (list of preloaded modules). The suffixes 'xx' on these items (which are not necessarily the same suffix) can be specified using three different DBCTL startup parameters. IMS.PROCLIB also holds the DFSPBxxx members containing IMS startup parameters that you have specifiedThe diagram also shows some other items that are related to, but not directly affected by, the DBCTL startup parameters:The library IMS.ACBLIBm, which contains database and program descriptions. The suffix 'm' on IMS.ACBLIB indicates the version of IMS.ACBLIB that is currently active, as indicated in IMS.MODSTAT, and it is the same as the suffix on IMS.MATRIX and IMS.MODBLKS.The status data set IMS.MODSTAT, that indicates which version of the libraries mentioned above is active (the suffix 'm' on IMS.MATRIX, IMS.MODBLKS, and IMS.ACBLIB indicates the version). IMS keeps two suffixed versions of the libraries, an active and an inactive version. To make changes to the libraries, the operator uses the IMS online change utility (OCU) to update the inactive library, and then switches the two libraries so the inactive library becomes the active library and vice versa.The DBCTL startup parameters can be created and selected as follows:During IMS system definition, using:The IMSCTRL macro. The SYSTEM= parameter in this macro specifies the type of system definition to be performed, such as ALL (batch and online system definition), MODBLKS (to generate control block members for resources to be added or changed online), or NUCLEUS (to generate an IMS nucleus, and control block members for all IMS control blocks). There are other options, and other parameters, on this and the following three macros which are not relevant here. The DATABASE macro. Using OCU, the IMS online change utility, this macro can define the contents of DFSDDIR in the IMS.MODBLKS library.The APPLCTN macro. Using OCU, this macro can define the contents of DFSPDIR in the IMS.MODBLKS library.The IMSGEN macro. The SUFFIX= parameter on this macro specifies the suffix character we have referred to as 'x' for DFSVNUCx (the IMS nucleus), DFSDDIRx (the DDIR), DFSPDIRx (the PDIR), and DFSAGT0x (the AGN table).At DBCTL startup, using a DFDPBDBC member which you have placed in IMS.PROCLIB. These members specify DBCTL control region execution parameters that override existing settings. You can create several, naming them DFDPBxxx, where xxx is three alphanumeric characters. The suffix of the member to be used at startup is specified on the RGSUF= parameter of the EXEC statement.At DBCTL startup, using parameters on an EXEC statement to override existing settings, as follows:The RGSUF= parameter, that selects one of your sets of DFDBPxxx override parameters to use during startup. The SUF= parameter, that specifies the suffix character we have referred to as 'x' for DFSVNUCx (the IMS nucleus), DFSDDIRx (the DDIR), DFSPDIRx (the PDIR), and DFSAGT0x (the AGN table). It overrides the suffix set by the IMSGEN macro.The VSPEC= parameter, that sets the suffix 'xx' on the DFSVSMxx member of IMS.PROCLIB.The FIX= parameter, that sets the suffix 'xx' on the DFSFIXxx member of IMS.PROCLIB.The PRLD= parameter, that sets the suffix 'xx' on the DFSMPLxx member of IMS.PROCLIB.The diagram also shows some other ways to affect the modules mentioned here:SMU, the IMS security maintenance utility, and OCU, the IMS online change utility, can be used to place AGNs (Application Group Names) in the AGN tables DFSAGT0x in IMS.MATRIX.ACBGEN, the IMS application control block generator, and OCU, the IMS online change utility, can be used to build IMS.ACBLIB.