{
        const IColumn & column = *key_columns[0];
        const ColumnFixedString & column_string = assert_cast<const ColumnFixedString &>(column);
        n = column_string.getN();
        chars = &column_string.getChars();
    }
    auto getKeyHolder(size_t row, [[maybe_unused]] Arena & pool) const
    {
        StringRef key(&(*chars)[row * n], n);
        if constexpr (place_string_to_arena)
        {
            return ArenaKeyHolder{key, pool};
        }
        else
        {
            return key;
        }
    }
protected:
    friend class columns_hashing_impl::HashMethodBase<Self, Value, Mapped, use_cache>;
};
class LowCardinalityDictionaryCache : public HashMethodContext