private Aggregation getCurrentAggregationBuffer(
        VectorAggregationBufferRow[] aggregationBufferSets,
        int aggregateIndex,
        int row) {
      VectorAggregationBufferRow mySet = aggregationBufferSets[row];
      Aggregation myagg = (Aggregation) mySet.getAggregationBuffer(aggregateIndex);
      return myagg;
    }
class for storing the current aggregate value.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/aggregates/VectorUDAFCountStar.java