The main problem area here is that in runs out of memory in SAP.This is a limitation of the interface SAP provides, you can do some workarounds to avoid this:
1. The Connector supports column-based slicing, creates qvd-files with n columns in each, which can be easily merged with the field "Commonkey".
2. Use the WHERE-clause and limit the number of rows of the object.
3. Use the SQL Connector instead, quite easy, plus you get possibilty to do incremental loads (template exists).