**Describe the bug**

Since we upgraded to 20.10.3.30, one of our clickhouse cluster takes much more time to start. (Up to 50 minutes, and before it took ~3 minutes)
The log file is filled with
>  <Debug> DiskLocal: Reserving 1.00 MiB on disk `default`, having unreserved 16.90 TiB

Additionally, the memory consumption increases, linearly, a lot (up to arround 230 G for us) and then drop back to normal values once clickhouse finished starting up. During that loading phase, a single CPU core is used at 100%.
If that memory is not available for the machine, clickhouse gets OOMed by the kernel.


**How to reproduce**
* Issue appeared after we upgraded to ClickHouse server version 20.10.3.30

* How could I find wich of our tables may be responsible for that ?


**Expected behavior**
A fast startup :)

size_t min_volume_index = 0,
        bool is_insert = false,
        DiskPtr selected_disk = nullptr) const;
    
    
    
    ReservationPtr balancedReservation(
        const StorageMetadataPtr & metadata_snapshot,
        size_t part_size,
        size_t max_volume_index,
        const String & part_name,
        const MergeTreePartInfo & part_info,
        MergeTreeData::DataPartsVector covered_parts,
        std::optional<CurrentlySubmergingEmergingTagger> * tagger_ptr,
        const IMergeTreeDataPart::TTLInfos * ttl_infos,
        bool is_insert = false);
    
    
    ReservationPtr makeEmptyReservationOnLargestDisk() const { return getStoragePolicy()->makeEmptyReservationOnLargestDisk(); }
    Disks getDisks() const { return getStoragePolicy()->getDisks(); }
    
    AlterConversions getAlterConversionsForPart(MergeTreeDataPartPtr part) const;
    
    
    SpacePtr getDestinationForMoveTTL(const TTLDescription & move_ttl, bool is_insert = false) const;
    
    
    bool isPartInTTLDestination(const TTLDescription & ttl, const IMergeTreeDataPart & part) const;