Usage

How to submit the UNLOAD statement

You submit the UNLOAD utility only through the batch command facility. You must run the batch command facility in local mode.

Using UNLOAD on an SQL-defined database

You can use the UNLOAD utility statement to unload and reload an SQL-defined database to make these changes:

Change area page ranges
Change page size
See EXPAND PAGE for complete information about changing a page size.
Change the maximum number of records per page

The page changes are specified in the DMCL definition.

Note: The modified DMCL must be available during the unload operation and during the reload operation.

You cannot make changes to table definitions in an SQL-defined database between the unload and reload steps.

Using UNLOAD on a non-SQL-defined database

You unload and reload a non-SQL-defined database in order to modify the database based on changes made to the schema or segment definition. These changes must be reflected in the subschema or DMCL used for the reload operation. An SQL-defined database must be reloaded into the same segment. You cannot reload it into another segment.

Note: The modified DMCL or subschema must be available during the unload operation and during the reload operation.

You can make the following changes by using UNLOAD and RELOAD:

Change area page ranges
Change page size
See EXPAND PAGE for complete information on changing a page size.
Change page ranges for record types
Reassign records to different areas
Change record placements within an area
Change record location modes
Store VIA records by means of a different set (as long as they already participate in the set)
Change compression and INDEX BLOCK CONTAINS options for indexes
Change area and page-range assignments for system-owned indexes
Change the maximum number of records per page

UNLOAD and ASF databases

If the UNLOAD utility is to be run against an ASF data or definition area, see the CA IDMS ASF User Guide for more information.

When not to use UNLOAD

The areas processed by the UNLOAD utility cannot contain any logically deleted records. Therefore, do not use it until you have removed all logically deleted records with the CLEANUP utility statement.

The UNLOAD utility cannot be used against native VSAM files.

During UNLOAD and RELOAD processing, record formats are preserved, that is, the layout of data within a record and record positions within sets. This limits the modifications that you can make during an unload/reload operation. For example, you cannot use an unload/reload operation to:

Remove a set
Remove a record type
Insert new data fields into a record
Change the order of a sorted set
Connect records to new sets
Change or delete record IDs
Change the size, location, or data type of sort or index keys
Change a set from unordered to ordered

These type of changes require other utilities, such as RESTRUCTURE, and possibly user-written programs.

Using UNLOAD and Mixed Page Groups

UNLOAD cannot process mixed page groups. The subschemas specified for the UNLOAD cannot contain areas that reside in page groups other than the page group for the segment being unloaded. If the environment has an EXIT34 installed that exit will be invoked. If the CA supplied EXIT34 is used (RHDCUX34) and has not been altered a message will be produced indicating that an unqualified FIND/OBTAIN DBKEY command has been issued. If the exit has been modified to abort the associated run-unit when this type of command is encountered, the UNLOAD utility will be abnormally terminated. You must use multiple invocations of the utility to process areas in different page groups.

UNLOAD and the DCMT VARY SEGMENT/AREA PERMANENT

If the UNLOAD utility is to be run with the purpose of changing an area's page range and that change includes changing the area's low page, it is recommended that none of the DCMT VARY SEGMENT/AREA commands using the PERMANENT option be issued against the original area(s). The PERMANENT feature is implemented by carrying the area's low-page number in the journals across cycles of the CV. Changing an area's low-page will prohibit future cycles of the CV to properly identify the area once the new page range is implemented.

If a DCMT VARY SEGMENT/AREA PERMANENT command is still in effect when the new page range is implemented, the area's usage-mode at startup will be determined by the value specified in the DMCL. The entry in the journals for the old area's page range will remain until the next format of the journals.

UNLOAD and the CLEANUP utility

If the area being unloaded contains logically deleted records, run the CLEANUP utility before running unload.

Note: For more information about making these kinds of changes, see the CA IDMS Database Administration Guide.