code: func newFixedLenColumn(elemLen, cap int) *column {
  	return &column{
  		elemBuf:    make([]byte, elemLen),
  		data:       make([]byte, 0, cap*elemLen),
  		nullBitmap: make([]byte, 0, cap>>3),
  	}
  }
docs: // newFixedLenColumn creates a fixed length column with elemLen and initial data capacity.