Why Use Unload/Reload?
The unload/reload upgrade avoids the upgradedb program (except for iidbdb), in favor of unloading the original Ingres databases to flat files, recreating the databases under Ingres, and then reloading the databases. This approach has the advantage of starting with clean databases, but requires more time and disk space than does the upgradedb method.
Note: Databases using the system-maintained logical key feature are best upgraded using upgradedb. Tables that contain SYSTEM_MAINTAINED table_key or object_key columns cannot be safely unloaded and reloaded without additional work. The reload step generates all new logical key values. If other tables reference the logical key columns, the new values must be manually propagated to those tables.