**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 :)

String getFullPathOnDisk(const DiskPtr & disk) const;
    
    
    DiskPtr tryGetDiskForDetachedPart(const String & part_name) const;
    DiskPtr getDiskForDetachedPart(const String & part_name) const;
    bool storesDataOnDisk() const override { return true; }
    Strings getDataPaths() const override;
    
    ReservationPtr reserveSpace(UInt64 expected_size) const;
    
    static ReservationPtr reserveSpace(UInt64 expected_size, SpacePtr space);
    static ReservationPtr tryReserveSpace(UInt64 expected_size, SpacePtr space);
    
    ReservationPtr reserveSpacePreferringTTLRules(
        const StorageMetadataPtr & metadata_snapshot,
        UInt64 expected_size,
        const IMergeTreeDataPart::TTLInfos & ttl_infos,
        time_t time_of_move,
        size_t min_volume_index = 0,
        bool is_insert = false,
        DiskPtr selected_disk = nullptr) const;
    ReservationPtr tryReserveSpacePreferringTTLRules(
        const StorageMetadataPtr & metadata_snapshot,
        UInt64 expected_size,
        const IMergeTreeDataPart::TTLInfos & ttl_infos,
        time_t time_of_move,