The command 'ALTER DATABASE FLASHBACK ON' turns on flashback logging (archive of undo), normally stored in the Flash or Fast Recovery Area (FRA). It is used to enable the "Flashback Database" feature.
Datapump does not use Flashback Database; it uses Flashback Query, which uses the UNDO tablespace. Since the Undo tablesapce works in a circular fashion, your ability to use Flashback Query by TIME or SCN will depend on its size and Undo retention policy.
Edited by: Markus Waldorf on Sep 4, 2010 10:42 AM