Time Consuming DB-Transaction

Hi list, I need to provide the facility to upload a large csv-file (>800kb) to my customer, do some expensive string comparison stuff (cut off empty lines or superfluous fields - Excel-Generated csv seems to be unpredictable in some cases; convert some of the fields - '3%' -> 3) and then load the file or insert each row into a postgres backend. This takes anywhere between 20 secs and 90 secs at the moment, and the file is likely to grow in the near future. How can I provide feedback to the user while keeping the db-transaction running and providing rollback facilities in case of a failure? tia. Hannes