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. 

{
    LOG_TRACE(log, "Executing DROP_RANGE {}", entry.new_part_name);
    auto drop_range_info = MergeTreePartInfo::fromPartName(entry.new_part_name, format_version);
    getContext()->getMergeList().cancelInPartition(getStorageID(), drop_range_info.partition_id, drop_range_info.max_block);
    queue.removePartProducingOpsInRange(getZooKeeper(), drop_range_info, entry);
    part_check_thread.cancelRemovedPartsCheck(drop_range_info);
    
    
    
    
    
    auto metadata_snapshot = getInMemoryMetadataPtr();
    DataPartsVector parts_to_remove;
    {
        auto data_parts_lock = lockParts();
        parts_to_remove = removePartsInRangeFromWorkingSetAndGetPartsToRemoveFromZooKeeper(NO_TRANSACTION_RAW, drop_range_info, data_parts_lock);
        if (parts_to_remove.empty())
        {