The challenge of transmitting large volumes of data to a warehouse is always one that must be carefully considered. Your options are limited in some ways since you feel that creating flat files is not an option, and based on your description, this is probably a good idea. You also mention a DB Link -- this is another nice option, but again not an option for you. So what else do we have? My suggestion would be transportable tablespaces (TT). The concept behind TT is that you can do a VERY quick export of the metadata and then you can copy the export file and the data files from your source system and then attach them to your database. Another option would be to export and import data; you could pipe the export and improve your performance. You could also create a standby database, but you would still have to transmit data to the warehouse.
I hope this gives you some food for thought.
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