presto-main/src/main/java/io/prestosql/operator/aggregation/NumericHistogramStateFactory.java/NumericHistogramStateFactory/getEstimatedSize
class NumericHistogramStateFactory:        @Override
        public long getEstimatedSize()
        {
            if (histogram == null) {
                return 0;
            }
            return histogram.estimatedInMemorySize();
        }