presto-main/src/main/java/io/prestosql/operator/aggregation/state/KeyValuePairsStateFactory.java/GroupedState/set
class GroupedState:        @Override
        public void set(KeyValuePairs value)
        {
            requireNonNull(value, "value is null");

            KeyValuePairs previous = get();
            if (previous != null) {
                size -= previous.estimatedInMemorySize();
            }

            pairs.set(getGroupId(), value);
            size += value.estimatedInMemorySize();
        }