For some reasons when we delete a MergeTree Part in atomic way something may go wrong - and leave the `delete_tmp_*` folder or it's part on disk. This may lead to a disk space consumption over time.

It's suggested to delete this folders at least at server start-up. Current solution with `clearOldTemporaryDirectories()` doesn't work because this method is called periodically from a thread without any locks or advisory on folders - it may cause the race conditions.
{
            Ordinary            = 0,    
            Collapsing          = 1,
            Summing             = 2,
            Aggregating         = 3,
            Replacing           = 5,
            Graphite            = 6,
            VersionedCollapsing = 7,
        };
        Mode mode;
        
        String sign_column;
        
        Names columns_to_sum;
        
        String version_column;
        
        Graphite::Params graphite_params;
        
        void check(const StorageInMemoryMetadata & metadata) const;