presto-main/src/main/java/io/prestosql/operator/aggregation/state/KeyValuePairsStateFactory.java/SingleState/getEstimatedSize
class SingleState:        @Override
        public long getEstimatedSize()
        {
            long estimatedSize = INSTANCE_SIZE;
            if (pair != null) {
                estimatedSize += pair.estimatedInMemorySize();
            }
            return estimatedSize;
        }