@Override
    public AggregationBuffer getNewAggregationBuffer() throws HiveException {
      AggregationBuffer result = new TimestampStatsAgg();
      reset(result);
      return result;
    }
GenericUDAFTimestampStatsEvaluator
High/low value will be saved in stats DB as long value representing seconds since epoch.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFComputeStats.java