Class VectorStream

bolt/serializers/PrestoSerializer.cpp:1226–1633

Appendable container for serialized values. To append a value at a time, call appendNull or appendNonNull first. Then call appendLength if the type has a length. A null value has a length of 0. Then call appendValue if the value was not null.

// type has a length. A null value has a length of 0. Then call appendValue if
// the value was not null.
class VectorStream {
 public:
  // This constructor takes an optional encoding and vector. In cases where the
  // vector (data) is not available when the stream is created, callers can also
  // manually specify the encoding, which only applies to the top level stream.
  // If both are specified, `encoding` takes precedence over the actual
  // encoding of `vector`. Only 'flat' encoding can take precedence over the
  // input data encoding.
  VectorStream(
      const TypePtr& type,
      std::optional<VectorEncoding::Simple> encoding,
      std::optional<VectorPtr> vector,
      StreamArena* streamArena,
      int32_t initialNumRows,
      bool useLosslessTimestamp)
      : type_(type),
        streamArena_(streamArena),
        encoding_(getEncoding(encoding, vector)),
        useLosslessTimestamp_(useLosslessTimestamp),
        nulls_(streamArena, true, true),
        lengths_(streamArena),
        values_(streamArena),
        isLongDecimal_(type_->isLongDecimal()) {
    if (initialNumRows == 0) {
      initializeHeader(typeToEncodingName(type), *streamArena);
      return;
    }

    if (encoding_.has_value()) {
      switch (encoding_.value()) {
        case VectorEncoding::Simple::CONSTANT: {
          initializeHeader(kRLE, *streamArena);
          isConstantStream_ = true;
          children_.emplace_back(std::make_unique<VectorStream>(
              type_,
              std::nullopt,
              std::nullopt,
              streamArena,
              initialNumRows,
              useLosslessTimestamp));
          return;
        }
        case VectorEncoding::Simple::DICTIONARY: {
          initializeHeader(kDictionary, *streamArena);
          values_.startWrite(initialNumRows * 4);
          isDictionaryStream_ = true;
          children_.emplace_back(std::make_unique<VectorStream>(
              type_,
              std::nullopt,
              std::nullopt,
              streamArena,
              initialNumRows,
              useLosslessTimestamp));
          return;
        }
        default:
          break;
      }