Method writeProjectionPartImpl

src/Storages/MergeTree/MergeTreeDataWriter.cpp:639–715

}

MergeTreeMetaBase::MutableDataPartPtr MergeTreeDataWriter::writeProjectionPartImpl(
    MergeTreeMetaBase & data,
    Poco::Logger * log,
    Block block,
    const StorageMetadataPtr & metadata_snapshot,
    MergeTreeMetaBase::MutableDataPartPtr && new_data_part)
{
    NamesAndTypesList columns = metadata_snapshot->getColumns().getAllPhysical().filter(block.getNames());
    MergeTreePartition partition{};
    IMergeTreeDataPart::MinMaxIndex minmax_idx{};
    new_data_part->setColumns(columns);
    new_data_part->partition = std::move(partition);
    new_data_part->minmax_idx = std::move(minmax_idx);

    if (new_data_part->isStoredOnDisk())
    {
        /// The name could be non-unique in case of stale files from previous runs.
        String full_path = new_data_part->getFullRelativePath();

        if (new_data_part->volume->getDisk()->exists(full_path))
        {
            LOG_WARNING(log, "Removing old temporary directory {}", fullPath(new_data_part->volume->getDisk(), full_path));
            new_data_part->volume->getDisk()->removeRecursive(full_path);
        }

        new_data_part->volume->getDisk()->createDirectories(full_path);
    }

    /// If we need to calculate some columns to sort.
    if (metadata_snapshot->hasSortingKey() || metadata_snapshot->hasSecondaryIndices())
        data.getSortingKeyAndSkipIndicesExpression(metadata_snapshot)->execute(block);

    Names sort_columns = metadata_snapshot->getSortingKeyColumns();
    SortDescription sort_description;
    size_t sort_columns_size = sort_columns.size();
    sort_description.reserve(sort_columns_size);

    for (size_t i = 0; i < sort_columns_size; ++i)
        sort_description.emplace_back(block.getPositionByName(sort_columns[i]), 1, 1);

    ProfileEvents::increment(ProfileEvents::MergeTreeDataProjectionWriterBlocks);

    /// Sort
    IColumn::Permutation * perm_ptr = nullptr;
    IColumn::Permutation perm;
    if (!sort_description.empty())
    {
        if (!isAlreadySorted(block, sort_description))
        {
            stableGetPermutation(block, sort_description, perm);
            perm_ptr = &perm;
        }
        else
            ProfileEvents::increment(ProfileEvents::MergeTreeDataProjectionWriterBlocksAlreadySorted);
    }

    /// This effectively chooses minimal compression method:
    ///  either default lz4 or compression method with zero thresholds on absolute and relative part size.