code: func (p PgXLog) Compare(xlog1, xlog2 xlog.Position) (int, error) {
  	p1, err := parse(xlog1)
  	if err != nil {
  		return 0, err
  	}
  	p2, err := parse(xlog2)
  	if err != nil {
  		return 0, err
  	}
  
  	if p1[0] == p2[0] && p1[1] == p2[1] {
  		return 0, nil
  	}
  	if p1[0] > p2[0] || p1[0] == p2[0] && p1[1] > p2[1] {
  		return 1, nil
  	}
  	return -1, nil
  }
docs: // Compare compares two xlog positions returning -1 if xlog1 < xlog2, 0 if xlog1
  // == xlog2, and 1 if xlog1 > xlog2.