Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

return Chunk(res.getColumns(), res.rows());
    }
private:
    const StorageStripeLog & storage;
    StorageSnapshotPtr storage_snapshot;
    ReadSettings read_settings;
    std::shared_ptr<const IndexForNativeFormat> indices;
    IndexForNativeFormat::Blocks::const_iterator index_begin;
    IndexForNativeFormat::Blocks::const_iterator index_end;
    size_t file_size;
    Block header;
    /** optional - to create objects only on first reading
      *  and delete objects (release buffers) after the source is exhausted
      * - to save RAM when using a large number of sources.
      */
    bool started = false;
    std::optional<CompressedReadBufferFromFile> data_in;
    std::optional<NativeReader> block_in;
    void start()
    {
        if (!started)
        {
            started = true;
            String data_file_path = storage.table_path + "data.bin";
            data_in.emplace(storage.disk->readFile(data_file_path, read_settings.adjustBufferSize(file_size)));
            block_in.emplace(*data_in, 0, index_begin, index_end);
        }
    }
};
class StripeLogSink final : public SinkToStorage