@Override
    public void reset(AggregationBuffer agg) throws HiveException {
      PercentileAgg percAgg = (PercentileAgg) agg;
      if (percAgg.counts != null) {
        percAgg.counts.clear();
      }
    }
A state class to store intermediate aggregation results.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFPercentileCont.java