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. 

{
    return MinimalisticDataPartChecksums::getSerializedString(checksums,
        getSettings()->use_minimalistic_checksums_in_zookeeper);
}
MergeTreeData::MutableDataPartPtr StorageReplicatedMergeTree::attachPartHelperFoundValidPart(const LogEntry& entry) const
{
    const MergeTreePartInfo actual_part_info = MergeTreePartInfo::fromPartName(entry.new_part_name, format_version);
    const String part_new_name = actual_part_info.getPartName();
    for (const DiskPtr & disk : getStoragePolicy()->getDisks())
        for (const auto it = disk->iterateDirectory(fs::path(relative_data_path) / "detached/"); it->isValid(); it->next())
        {