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. 

out.finalizePart(new_data_part, sync_on_insert);
    try
    {
        MergeTreeData::Transaction transaction(*this, NO_TRANSACTION_RAW);
        auto replaced_parts = renameTempPartAndReplace(new_data_part, transaction, data_part_storage_builder);
        if (!replaced_parts.empty())
        {
            Strings part_names;
            for (const auto & part : replaced_parts)
                part_names.emplace_back(part->name);
            
            
            
            
            
            
            
            
            throw Exception(ErrorCodes::INCORRECT_DATA, "Tried to create empty part {}, but it replaces existing parts {}.", lost_part_name, fmt::join(part_names, ", "));
        }
        lockSharedData(*new_data_part, false, {});
        while (true)
        {