The database unload/reload method ensures a clean start with a fresh database. Depending on the kind of table data, additional disk space may be needed to perform the unloading and reloading; the space could be as large as three to five times the space of the database that is to be upgraded. For example, compressed tables with wide char or varchar columns can expand substantially when unloaded.

The unload/reload process takes longer than upgradedb, thus increasing the downtime of the production system. However, it ensures a clean final installation.

A database that has been running for years, perhaps surviving a number of system crashes and hardware failures, may have suffered hidden damage that can confuse the upgradedb utility. For example, a database that is used by a small department or group of people may not be maintained as well as a production database. Such a database may have work tables owned by a user who no longer exists, or may be missing table data files. An unload/reload upgrade may be a better choice for this database.

The typical unload/reload upgrade uses the original Ingres installation as a base. The system databases iidbdb and imadb are upgraded in-place with upgradedb, even if user databases are unloaded/reloaded. A variation of the unload/reload method uses a brand new installation (perhaps even on a different machine). When this is done, additional work is needed to transfer iidbdb information (users, groups, roles, and database and installation privileges) to the new installation.