Migration considerations for dynamic definition of MSC resources

There are several considerations for migrating to IMS 15 support for the dynamic definition of MSC resources.

To migrate to using dynamic definition of MSC resources, evaluate existing transaction, LTERM, and MSNAME names for conflicts with dynamic MSC. Dynamic MSC reserves additional name prefixes, including MSNS and MSNI. If you already have existing transaction, LTERM, or MSNAMEs defined that start with the prefix MSNS or MSNI, the CREATE MSNAME command might not complete successfully. The CREATE MSNAME command defines an internal system MSNAME with the naming convention MSNIxxxx, where xxxx is the link number. If MSNIxxxx already exists as an LTERM, transaction, or MSNAME, the CREATE MSNAME command will fail.

The QUERY LTERM, QUERY MSLINK, QUERY MSNAME, and QUERY MSPLINK commands are changed to include L before all local headers in command output, as preconditioning to distinguish from the global output fields for the IMSRSC repository. If you have automation that looks for the headers, it might need to change to look for the new local headers that have L at the beginning.

Automation might need to be changed if it issues the following commands:
  • /DISPLAY ASMT MSPLINK, QUERY MSLINK, or QUERY MSPLINK commands, because the resources are now displayed in alphabetic order instead of in system definition order.
  • QUERY LTERM, QUERY MSLINK, QUERY MSNAME, or QUERY MSPLINK commands that parse the output headers, because all local headers now have an L prefix, to identify them as local values.
  • QUERY MSLINK specified with SHOW(ALL), because SHOW(ALL) now displays the column for definitional attribute BACKUP.
  • QUERY MSPLINK specified with SHOW(ALL), because SHOW(ALL) now displays columns for definitional attributes ASR, BACKUP, BUFSIZE, MAXSESS, and MODETBL.

IMS 14 manages link numbers differently after a cold start when logical links are deleted and re-created. Update your operating procedures to use link names instead of link numbers. The numbers for links remain the same across warm and emergency restarts, even if there are number gaps caused by deleted links. If links are created and deleted dynamically, resulting in gaps in link numbers, when an IMS system is cold started, the gaps are removed and the link numbers of the logical links that followed the gap are adjusted.

Exit routines that access remote logical terminal blocks (RCNTs) must be updated to use the FIND and SCAN control block callable services to access the RCNTs. In IMS 13 and earlier, exit routines could access RCNTs by referencing the RCNTs in the SCDRCNTM field of the IMS system contents directory (SCD). In IMS 15, exit routines can no longer use the SCDRCNTM field to access RCNTs. For more information about the FIND and SCAN control block callable services, see IMS Callable Control Block Services requests.

After migration, perform the following procedure to clean up system generation definitions:
  1. Remove the MSC definitions from the stage 1 system definition, which include the following items:
    • MSPLINK, MSLINK, MSNAME, and NAME macros
    • MSVID and SYSTEM=(MSVERIFY) parameters in the IMSCTRL macro
    • SYSID parameter in the APPLCTN and TRANSACT macros
  2. Run system generation.