**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 :)

DataTypePtr getPartitionValueType() const;
    
    Block getSampleBlockWithVirtualColumns() const;
    
    
    Block getBlockWithVirtualPartColumns(const MergeTreeData::DataPartsVector & parts, bool one_part, bool ignore_empty = false) const;
    
    SimpleIncrement insert_increment;
    bool has_non_adaptive_index_granularity_parts = false;
    
    mutable std::atomic_bool has_lightweight_delete_parts = false;
    
    
    
    
    
    
    DataParts currently_moving_parts;
    
    mutable std::mutex moving_parts_mutex;
    PinnedPartUUIDsPtr getPinnedPartUUIDs() const;
    
    virtual bool scheduleDataProcessingJob(BackgroundJobsAssignee & assignee) = 0;
    
    bool scheduleDataMovingJob(BackgroundJobsAssignee & assignee);
    bool areBackgroundMovesNeeded() const;
    
    
    virtual void lockSharedData(const IMergeTreeDataPart &, bool = false, std::optional<HardlinkedFiles> = {}) const {}