Changing or adding IMS.ACBLIB members online

In an IMSplex environment, you can use the ACB member online change (OLC) function to add or change individual members of the ACB library, or the entire ACB library, and bring these new or changed members online without quiescing the IMSplex or refreshing the active ACB library.

Members that are not affected by the member OLC are not quiesced.

You can make online changes to the ACB library in IMSplex environments in which:

  • A single IMS system comprises the IMSplex. In this configuration, IMS must use the OLCSTAT data set with a CSL that consists of an OM and SCI. An RM is not required.
  • Multiple IMS systems comprise the IMSplex. In this configuration, each IMS system must use the same shared OLCSTAT data set, or each system must use its own local OLCSTAT data set. The CSL must consist of an OM, an SCI, and an RM. Although a resource structure is recommended, it is not required.

Global online change for ACBLIB members can only be performed in an IMSplex.

You can specify whether the ACBLIB member is shared or dedicated in the IMSplex. The following example highlights how the ACBLIB member online change process can be coordinated among all IMS systems that share the OLCSTAT data set:

  • OM chooses an IMS system to be the command master IMS.
  • The command master IMS coordinates the member OLC process with other IMS systems sharing the OLCSTAT data set using RM.
  • ACBSHR= must be specified as Y or N in the DFSCGxxx or DFSDFxxx PROCLIB member.
    • Y– Indicates that all of the IMS systems in the OLCSTAT are using the same active and inactive ACBLIB.
    • N– Indicates that each IMS in the OLCSTAT is using its own dedicated active and inactive ACBLIB.
  • All IMS systems in the IMSplex that share the OLCSTAT data set must specify the value of ACBSHR=.
  • The member OLC updates all the active ACBLIBs, whether or not they are shared.

The ACB member online change uses IMS type-2 commands only. The commands that are involved in performing an ACB library member online change are:

  • INITIATE OLC PHASE(PREPARE)
  • INITIATE OLC PHASE(COMMIT)
  • TERMINATE OLC
  • QUERY MEMBER TYPE(IMS)
  • QUERY OLC SHOW(RSCLIST)

By default, when a DBD is specified on the NAME keyword of the INITIATE OLC PHASE(PREPARE) TYPE(ACBMBR) command, the ACB member online change (OLC) function automatically copies all associated PSBs and externally referenced DBDs from the staging ACB library to active ACB library. Depending on the number of PSBs and DBDs, the amount of time required for the copying process can be significant.

In many cases, you can significantly reduce the amount of time the ACB member online change function takes by specifying OPTION(NAMEONLY) on the INITIATE OLC PHASE(PREPARE) TYPE(ACBMBR) command. The NAMEONLY option limits the processing of the ACB member online change function to only the DBDs and PSBs that are specified in NAME() keyword of the command.

If you want to fall back to the previous version of the changed resource, perform a full online change process with a full library switch.

To perform an ACB member online change:

Procedure

  1. Define the IMS system with online change capability by removing local MODSTAT definitions and defining the OLCSTAT data set in the DFSCGxxx PROCLIB member.
  2. Run the PSB generation to generate or update PSBLIB members.
  3. Run the DBD generation to generate or update DBDLIB members.
  4. Run the ACB generation to create an executable ACBLIB member in a staging ACB library.

    The staging ACB library can be a clone or a subset of the active ACB library.

  5. Optionally, create a backup copy of the active ACBLIB member for fallback purposes; you can use the Online Change Copy utility (DFSUOCU0) to do this.
  6. Issue the INITIATE OLC command with the TYPE(ACBMBR) parameter to copy the updated or new member from the staging library to the active library.

    If your ACBs are in 64-bit storage, the ACB members that are affected by the online change process are removed from the non-resident pool and deleted from the 64-bit pool. The next time an application is scheduled that needs the new or updated ACB members, the members are read from the ACB library and copied to the non-resident pool for execution and are also copied to the 64-bit pool.

If you want to fall back to the previous version of the changed resource, perform a full online change process with a full library switch.