public Statistics scaleToRowCount(long newRowCount, boolean downScaleOnly) {
    Statistics ret = clone();
    if (numRows == 0) {
      return ret;
    }
    if (downScaleOnly && newRowCount >= numRows) {
      return ret;
    }
    // FIXME: using real scaling by new/old ration might yield better results?
    ret.numRows = newRowCount;
    ret.dataSize = StatsUtils.safeMult(getAvgRowSize(), newRowCount);
    return ret;
  }
Statistics. Describes the output of an operator in terms of size, rows, etc
based on estimates.
ql/src/java/org/apache/hadoop/hive/ql/plan/Statistics.java