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;
    if (num_data_files)
        total_rows = data_files[INDEX_WITH_REAL_ROW_COUNT].marks.empty() ? 0 : data_files[INDEX_WITH_REAL_ROW_COUNT].marks.back().rows;
    else
        total_rows = 0;
}
std::optional<UInt64> StorageLog::totalRows(const Settings &) const
{
    if (use_marks_file && marks_loaded)
        return total_rows;
    if (!total_bytes)
        return 0;
    return {};
}
std::optional<UInt64> StorageLog::totalBytes(const Settings &) const