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. 

{
    ISerialization::SerializeBinaryBulkSettings settings;
    const auto & [name, type] = name_and_type;
    auto serialization = type->getDefaultSerialization();
    serialization->enumerateStreams([&] (const ISerialization::SubstreamPath & path)
    {
        String data_file_name = ISerialization::getFileNameForStream(name_and_type, path);
        auto it = streams.find(data_file_name);
        if (it == streams.end())
        {
            const auto & data_file_it = storage.data_files_by_names.find(data_file_name);
            if (data_file_it == storage.data_files_by_names.end())
                throw Exception("Logical error: no information about file " + data_file_name + " in StorageLog", ErrorCodes::LOGICAL_ERROR);
            const auto & data_file = *data_file_it->second;
            const auto & columns = metadata_snapshot->getColumns();
            it = streams.try_emplace(data_file.name, storage.disk, data_file.path,
                                     storage.file_checker.getFileSize(data_file.path),
                                     columns.getCodecOrDefault(name_and_type.name),
                                     storage.max_compress_block_size).first;
        }
        auto & stream = it->second;
        if (stream.written)
            return;
    });
    settings.getter = createStreamGetter(name_and_type);