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. 

{
    if (!use_marks_file || marks_loaded)
        return;
    size_t num_marks = 0;
    if (disk->exists(marks_file_path))
    {
        size_t file_size = disk->getFileSize(marks_file_path);
        if (file_size % (num_data_files * sizeof(Mark)) != 0)
            throw Exception("Size of marks file is inconsistent", ErrorCodes::SIZES_OF_MARKS_FILES_ARE_INCONSISTENT);
        num_marks = file_size / (num_data_files * sizeof(Mark));
        for (auto & data_file : data_files)
            data_file.marks.resize(num_marks);
        std::unique_ptr<ReadBuffer> marks_rb = disk->readFile(marks_file_path, ReadSettings().adjustBufferSize(32768));
        for (size_t i = 0; i != num_marks; ++i)
        {
            for (auto & data_file : data_files)
            {
                Mark mark;
                mark.read(*marks_rb);
                data_file.marks[i] = mark;
            }
        }
    }
    marks_loaded = true;
    num_marks_saved = num_marks;
    
    updateTotalRows(lock);
}
void StorageLog::saveMarks(const WriteLock & )