Method MergeTreeReaderCompact

src/Storages/MergeTree/MergeTreeReaderCompact.cpp:135–257

}

MergeTreeReaderCompact::MergeTreeReaderCompact(
    DataPartCompactPtr data_part_,
    NamesAndTypesList columns_,
    const StorageMetadataPtr & metadata_snapshot_,
    UncompressedCache * uncompressed_cache_,
    MarkCache * mark_cache_,
    MarkRanges mark_ranges_,
    MergeTreeReaderSettings settings_,
    ValueSizeMap avg_value_size_hints_,
    const ReadBufferFromFileBase::ProfileCallback & profile_callback_,
    clockid_t clock_type_)
    : IMergeTreeReader(
        std::move(data_part_),
        std::move(columns_),
        metadata_snapshot_,
        uncompressed_cache_,
        mark_cache_,
        std::move(mark_ranges_),
        std::move(settings_),
        std::move(avg_value_size_hints_))
{
    try
    {
        size_t columns_num = columns.size();

        column_positions.resize(columns_num);
        read_only_offsets.resize(columns_num);
        auto name_and_type = columns.begin();
        auto compact_part = std::dynamic_pointer_cast<const MergeTreeDataPartCompact>(data_part);
        if (!compact_part)
            throw Exception("Can not convert part into MergeTreeDataPartCompact in MergeTreeReaderCompact.", ErrorCodes::LOGICAL_ERROR);
        for (size_t i = 0; i < columns_num; ++i, ++name_and_type)
        {
            if (name_and_type->name == "_part_row_number")
                continue;

            if (name_and_type->isSubcolumn())
            {
                auto storage_column_from_part = getColumnFromPart(
                    {name_and_type->getNameInStorage(), name_and_type->getTypeInStorage()});

                if (!storage_column_from_part.type->tryGetSubcolumnType(name_and_type->getSubcolumnName()))
                    continue;
            }

            NameAndTypePair column_from_part = getColumnFromPart(*name_and_type);

            auto position = compact_part->getColumnPositionWithoutMap(column_from_part.name);
            if (!position && typeid_cast<const DataTypeArray *>(column_from_part.type.get()))
            {
                /// If array of Nested column is missing in part,
                /// we have to read its offsets if they exist.
                position = findColumnForOffsets(column_from_part.name);
                read_only_offsets[i] = (position != std::nullopt);
            }

            column_positions[i] = std::move(position);
        }