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 (!path_to_set_hardlinked_files.empty() && !hardlinked_files.empty())
                {
                    std::string data = boost::algorithm::join(hardlinked_files, "\n");
                    
                    
                    
                    ops.emplace_back(zkutil::makeSetRequest(path_to_set_hardlinked_files, data, -1));
                }
                Coordination::Responses responses;
                auto error = zookeeper->tryMulti(ops, responses);
                if (error == Coordination::Error::ZOK)
                {
                    created = true;
                    break;
                }
                else if (error == Coordination::Error::ZNONODE && mode != zkutil::CreateMode::Persistent)
                {
                    throw Exception(ErrorCodes::NOT_FOUND_NODE, "Cannot create ephemeral zero copy lock {} because part was unlocked from zookeeper", zookeeper_node);
                }
            }
            else
            {
                Coordination::Requests ops;
                if (!path_to_set_hardlinked_files.empty() && !hardlinked_files.empty())
                {
                    std::string data = boost::algorithm::join(hardlinked_files, "\n");
                    
                    
                    
                    ops.emplace_back(zkutil::makeSetRequest(path_to_set_hardlinked_files, data, -1));