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. 

const DataPartPtr & part, std::optional<MergeTreeData::HardlinkedFiles> hardlinked_files)
{
    auto zookeeper = getZooKeeper();
    while (true)
    {
        Coordination::Requests ops;
        NameSet absent_part_paths_on_replicas;
        lockSharedData(*part, false, hardlinked_files);
        
        checkPartChecksumsAndAddCommitOps(zookeeper, part, ops, part->name, &absent_part_paths_on_replicas);
        
        if (transaction.isEmpty())
            return {};
        
        if (!absent_part_paths_on_replicas.empty())
        {
            Coordination::Requests new_ops;
            for (const String & part_path : absent_part_paths_on_replicas)
            {
                
                new_ops.emplace_back(zkutil::makeCreateRequest(part_path, "", zkutil::CreateMode::Persistent));
                new_ops.emplace_back(zkutil::makeRemoveRequest(part_path, -1));
            }