Project (UnaryNode) is way too aggressive in estimating statistics

  override def statistics: Statistics = {
    // There should be some overhead in Row object, the size should not be zero when there is
    // no columns, this help to prevent divide-by-zero error.
    val childRowSize = child.output.map(_.dataType.defaultSize).sum + 8
    val outputRowSize = output.map(_.dataType.defaultSize).sum + 8
    // Assume there will be the same number of rows as child has.
    var sizeInBytes = (child.statistics.sizeInBytes * outputRowSize) / childRowSize
    if (sizeInBytes == 0) {
      // sizeInBytes can't be zero, or sizeInBytes of BinaryNode will also be zero
      // (product of children).
      sizeInBytes = 1
    }

    child.statistics.copy(sizeInBytes = sizeInBytes)
  }