During UNLOAD processing, an area sweep is performed, unloading all CALC, DIRECT, and unowned VIA records. At the same time, the area sweep extracts information for all indexes regardless of whether or not the index has been specified for the data area being unloaded.
After unloading the owner of a VIA set, the area sweep is interrupted to unload all the members of the set.
When unloading a CALC record for which duplicates are allowed, the CALC set is walked in the prior direction to determine the relative position of the record with respect to other record occurrences with duplicate keys.
Non-SQL-defined sets can be partially unloaded
Records in an area being unloaded or reloaded can have set connections (as owners or members) to records in areas not being processed in the same run.
For example, a CALC record in an area being unloaded can own a VIA member in an area that is not being unloaded.
The UNLOAD utility will keep track of the set connections, and the connections will be rebuilt when the records are reloaded.
Note: UNLOAD cannot process mixed page groups and will issue an error message if mixed page groups are encountered. You must use multiple invocations of the utility to process different page groups.
SQL-defined segments
Area and table stamps are unloaded during the UNLOAD steps of an SQL-defined database and are reloaded during RELOAD processing. For this reason, you must format the affected areas using the FILE option between the unload and reload operations.
The one exception to this is when unloading and reloading the DDLCATLOD area in a segment defined for SQL. In this case, either format by area or use the INSTALL STAMPS utility before reloading the data.
DIRECT records and their VIA clusters
Since DIRECT records have been placed on a specific page by a user, it may be difficult for the UNLOAD utility to determine where they should be placed in the new area. If a DIRECT record's old page exists in the new area, the RELOAD attempts to place the occurrence on the same page. However, if the old page does not exist in the new page range, the occurrence is targeted to the low page of the new area.
If a DIRECT record owns a VIA record, the members are stored in their new area proportional to their owner's position in its old area. If the owners and members reside in the same area and the page range has been extended or completely changed, the VIA cluster may not be on the same page as the owner. If this is not acceptable, the user may want to consider using a user-written program to unload the database and the FASTLOAD utility to reload the area.
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