public Object get(int evaluatorIndex, Range range) {
      if (cache[evaluatorIndex].containsKey(range)) {
        hit += 1;
      } else {
        miss += 1;
      }
      return cache[evaluatorIndex].get(range);
    }
Cache for storing aggregated values that were already calculated within a partition - used for
PTF functions. This cache can lead to performance improvement when PTFPartition would have to
calculate a particular aggregation for the same range again and again. The caching relies on the
fact that evaluators are deterministic in a sense that they'll give the same result for the same
range in the same partition (no matter for which row is the current target).
ql/src/java/org/apache/hadoop/hive/ql/exec/PTFValueCache.java