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. 

{
            tryLogCurrentException(log, "Failed to remove some parts from memory, or write info about them into part log");
        }
    };
    
    if (!parts_to_delete_only_from_filesystem.empty())
    {
        
        
        
        delete_parts_from_fs_and_rollback_in_case_of_error(parts_to_delete_only_from_filesystem, "old duplicate");
    }
    
    NameSet part_names_to_retry_deletion;
    try
    {
        Strings part_names_to_delete_completely;
        for (const auto & part : parts_to_delete_completely)
            part_names_to_delete_completely.emplace_back(part->name);
        LOG_DEBUG(log, "Removing {} old parts from ZooKeeper", parts_to_delete_completely.size());
        removePartsFromZooKeeper(zookeeper, part_names_to_delete_completely, &part_names_to_retry_deletion);
    }
    catch (...)
    {
        LOG_ERROR(log, "There is a problem with deleting parts from ZooKeeper: {}", getCurrentExceptionMessage(true));
    }
    
    auto num_reliably_deleted_parts = parts_to_delete_completely.size() - part_names_to_retry_deletion.size();
    LOG_DEBUG(log, "Removed {} old parts from ZooKeeper. Removing them from filesystem.", num_reliably_deleted_parts);