Removing DBD and PSB instances from the IMS catalog

You can remove the segments that represent individual DBD and PSB instances from the DBD and PSB records in the IMS catalog by using the IMS Catalog Record Purge utility (DFS3PU10).

You can also use the IMS Catalog Record Purge utility to delete all DBD instances of a particular DBD version from a DBD record in the IMS catalog. When a DBD version is deleted, all DBD instances of the DBD version are deleted from the DBD record. After deletion, the version of the DBD no longer exists in the IMS catalog.

When the IMS management of ACBs function is enabled, the IMS Catalog Record Purge utility deletes from the IMS directory the DBD and PSB instances that are also deleted from the IMS catalog. The DBD and PSB instances that are deleted from the IMS directory are also deleted from the directory staging data set.

The IMS Catalog Record Purge utility issues a CHKP (checkpoint) call to commit updates to the IMS catalog after every 200 updates. After 200 updates are made, the updates are committed to the IMS catalog only after the DBDs and PSBs that were identified for deletion since the previous CHKP call are deleted from the IMS directory.

To help avoid the unintentional deletion of DBD or PSB segments that you still need, you can define retention criteria for the DBD and PSB records in the IMS catalog. Based on the retention criteria in effect for each record in the catalog, the analysis function of the IMS Catalog Record Purge utility identifies and creates DELETE statements for the DBD or PSB segment instances that are eligible for deletion.

Retention criteria specific to a DBD or PSB record is set by the UPDATE control statement of the IMS Catalog Record Purge utility and are stored in the HEADER segment of the record. If no retention criteria is specified for a given record, catalog records are subject to the default retention criteria that is set by the RETENTION statement in the CATALOG section of the DFSDFxxx member of the IMS.PROCLIB data set.

The retention criteria includes the minimum number of segment instances IMS must retain in a DBD or PSB record and the minimum period of time segment instances must be retained before they can be deleted. By default, IMS retains a minimum DBD and PSB instances a record. There is no default for the period of time an instance must be retained. Periods of time are measured in days.

For example, if the number of instances of DBD or PSB segments in a record is equal to or less than the retention number that is set for the record, no instances can be deleted. If the number of days that a DBD or PSB instance has been in the IMS catalog is equal to or less than the retention period defined for the DBD or PSB record that contains it, the DBD or PSB instance cannot be deleted.

When you define your retention criteria for the segment instances in DBD and PSB records, keep in mind that each additional instance increases the amount of storage that is required for the IMS catalog.