Controlling online change

If you modify a shared database online in a sharing environment, you must coordinate the sequence of /MODIFY commands across all sharing IMS systems.

Procedure

  1. Stop the databases you want to modify in all IMS online systems using that database.
  2. Perform the online change on all sharing IMS systems
  3. Restart the shared databases only when the /MODIFY command sequences are complete in all affected IMS systems.
If any of the data-sharing IMS systems also physically share any of the ACBLIB, FORMAT, or MODBLKS libraries, you must ensure that these IMS systems use the same designated active library, for example, IMS.ACBLIBA.

Each system keeps track of its active libraries in the IMS.MODSTAT data set. Performing an online change in only one IMS system could result in the individual IMS systems' using different control blocks, which can cause unpredictable errors in a data-sharing environment.

Also, if any library is shared, ensure that the Online Change Copy utility (DFSUOCU0) updates only inactive libraries.