code: public int sendBuffer1(SingleElementPushBackIterator<IN1> input) throws IOException {
  		if (serializer1 == null) {
  			IN1 value = input.next();
  			serializer1 = getSerializer(value);
  			input.pushBack(value);
  		}
  		return sendBuffer(input, serializer1);
  	}
docs: Extracts records from an iterator and writes them to the memory-mapped file. This method assumes that all values
  in the iterator are of the same type. This method does NOT take care of synchronization. The caller must
  guarantee that the file may be written to before calling this method.
  
  @param input iterator containing records
  @return size of the written buffer
  @throws IOException