Changing databases dynamically in online systems

Dynamic resource definition allows you to add new databases to an online IMS system, update certain attributes of the database online, or remove databases from the online IMS system without requiring you to shut IMS down or perform any of the system definition process.

To use dynamic resource definition, the feature must be enabled in your IMS system.

The type-2 commands that support changing databases by using dynamic resource definition include:

  • CREATE DB
  • DELETE DB
  • UPDATE DB

By using the QUERY DB command, you can display the database attributes that can be changed by the other commands.

Dynamic resource definition also allows you to define and store database resource descriptors, which can be used as a template to create new databases with common attributes. For example, when adding a database to an online system by using the CREATE DB command, instead of specifying each attribute individually, you can specify CREATE DB NAME(db_name) LIKE(DESC(db_desc_name)). The LIKE() parameter can also be used to create new databases based on existing databases or database descriptors.

To save changes made to databases online by using dynamic resource definition across cold starts, the database definitions must be either:
  • Exported, either by the EXPORT DEFN command or automatic export, to the resource definition data set (RDDS) or the IMSRSC repository if IMS is enabled with the repository
  • Added to the IMS MODBLKS data set by system definition and then imported during cold start. Across warm starts and emergency restarts, IMS recovers dynamic resource definition changes from the logs.

If IMS is enabled to use the IMSRSC repository, resource definitions in the IMS change list are read at the end of warm or emergency restart. IMS calls the Resource Manager (RM) to read the change list for the IMS. The IMS change list is maintained by RM in the repository.

If a change list exists, IMS imports the stored resource definitions from the IMSRSC repository for all the resources and descriptors in the change list. The IMS change list is processed after the IMS log is processed. The resources and descriptors in the change list are quiesced and are not available for use until the stored resource definitions are imported from the repository. The change list for the IMS system is deleted at the end of warm or emergency restart or at the end of IMS cold start.