Learn more about the IMS online reorganization process

End-to-end reorganization solution

IBM® IMS™ Online Reorganization Facility for z/OS® analyzes and evaluates space management conditions against user-defined policies to determine when thresholds have been breached. It detects problems before they can negatively impact IMS applications. You can schedule when you want to reorganize online databases by predefining an online reorganization window, helping save DBA resources, CPU time and increasing database availability.


The verification phase is the first phase of the online reorganization process. IMS Online Reorganization Facility for z/OS uses this phase to validate that the IMS database can be reorganized. The tool checks the IMS release and component levels, the DBRC registration and database DBD definitions, the tool control statements, and the shadow and temporary data sets are allocated correctly. The reorganization continues if this verification step completes successfully.


The IMS databases are briefly paused to allow the database buffers to be flushed to the IMS database data sets. This ensures that the latest updates are captured in the original IMS database data sets. Then the original IMS database data sets are copied to the shadow IMS database data sets. When this copy is completed, a second brief pause is performed to capture any updates that were made to the original IMS database data sets. These updates are also applied to the shadow data sets.


Once the shadow IMS database data sets are created, they are unloaded using the unload tool and reloaded using the load tool. If there are secondary indexes, they are also rebuilt. Internal logical relationships are resolved and updated using the prefix resolution tool. The reorganized IMS shadow databases are image copied with the image copy tool and can be pointer checked with the pointer checker tool.


When the reorganization of the shadow data sets has completed, the original IMS database data sets are swapped with the reorganized shadow IMS database data sets. IMS DBRC is notified with the REORG database status. If the IMS DBD database definitions change, the IMS Online Reorganization Facility performs an ACBGEN. Finally, the IMS database is restarted internally by the tool with the /START command and the takeover phase is completed.


In the completion step, the final reports are created and the shadow IMS database data sets are deleted.

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