You can configure the Update Strategy transformation to either pass rejected rows to the next transformation or drop them. By default, the Integration Service forwards rejected rows to the next transformation. The Integration Service flags the rows for reject and writes them to the session reject file. If you do not select Forward Rejected Rows, the Integration Service drops rejected rows and writes them to the session log file.
If you enable row error handling, the Integration Service writes the rejected rows and the dropped rows to the row error logs. It does not generate a reject file. If you want to write the dropped rows to the session log in addition to the row error logs, you can enable verbose data tracing.