SelectionVector2 contains list of indexes for the rows that RemovingRecordBatch can copy from underlying RecordBatch. SV2 is created by operator like Filter, Limit, etc to provide the selected rows from underlying buffer. Later then RemovingRecordBatch copies the rows based on indexes in SelectionVector2 to the output container of type NONE.
For cases when all the rows needs to be copied by RemovingRecordBatch from incoming batch, it can be improved to do full transfer of ValueVectors from input to output container instead of row by row copy. For example if for an incoming batch all rows are selected by the Filter condition in FilterRecordBatch, it will prepare an SV2 with all the record rowIndex. Later RemovingRecordBatch downstream of Filter can potentially do just transfer instead of row by row copy.