public void addBasicStats(Statistics stats) {
    dataSize = StatsUtils.safeAdd(dataSize, stats.dataSize);
    numRows = StatsUtils.safeAdd(numRows, stats.numRows);
    basicStatsState = inferColumnStatsState(basicStatsState, stats.basicStatsState);
  }
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