protected void resetAggregations(AggregationBuffer[] aggs) throws HiveException {
    for (int i = 0; i < aggs.length; i++) {
      aggregationEvaluators[i].reset(aggs[i]);
    }
  }
@return the size of each row
ql/src/java/org/apache/hadoop/hive/ql/exec/GroupByOperator.java