@Override
    public String getStatistics() {
      return String.format(
          "PTFValueCache.InstrumentedCacheHandler statistics: put: %d, evict: %d, hit: %d, miss: %d",
          put, evict, hit, miss);
    }
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