Method ConfigureDictionary

cpp/src/parquet/column_reader.cc:737–771

  }

  void ConfigureDictionary(const DictionaryPage* page) {
    int encoding = static_cast<int>(page->encoding());
    if (page->encoding() == Encoding::PLAIN_DICTIONARY ||
        page->encoding() == Encoding::PLAIN) {
      encoding = static_cast<int>(Encoding::RLE_DICTIONARY);
    }

    auto it = decoders_.find(encoding);
    if (it != decoders_.end()) {
      throw ParquetException("Column cannot have more than one dictionary.");
    }

    if (page->encoding() == Encoding::PLAIN_DICTIONARY ||
        page->encoding() == Encoding::PLAIN) {
      auto dictionary = MakeTypedDecoder<DType>(Encoding::PLAIN, descr_, pool_);
      dictionary->SetData(page->num_values(), page->data(), page->size());

      // The dictionary is fully decoded during DictionaryDecoder::Init, so the
      // DictionaryPage buffer is no longer required after this step
      //
      // TODO(wesm): investigate whether this all-or-nothing decoding of the
      // dictionary makes sense and whether performance can be improved

      std::unique_ptr<DictDecoder<DType>> decoder = MakeDictDecoder<DType>(descr_, pool_);
      decoder->SetDict(dictionary.get());
      decoders_[encoding] =
          std::unique_ptr<DecoderType>(dynamic_cast<DecoderType*>(decoder.release()));
    } else {
      ParquetException::NYI("only plain dictionary encoding has been implemented");
    }

    new_dictionary_ = true;
    current_decoder_ = decoders_[encoding].get();
    ARROW_DCHECK(current_decoder_);
  }

  // Initialize repetition and definition level decoders on the next data page.