**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 :)

const MergeListEntry * merge_entry);
    
    
    
    virtual bool partIsAssignedToBackgroundOperation(const DataPartPtr & part) const = 0;
    
    
    
    
    virtual MutationCommands getFirstAlterMutationCommandsForPart(const DataPartPtr & part) const = 0;
    
    bool movePartsToSpace(const DataPartsVector & parts, SpacePtr space);
    
    static BackupEntries backupParts(const DataPartsVector & data_parts, const String & data_path_in_backup);
    class RestoredPartsHolder;
    
    void restorePartsFromBackup(RestorerFromBackup & restorer, const String & data_path_in_backup, const std::optional<ASTs> & partitions);
    void restorePartFromBackup(std::shared_ptr<RestoredPartsHolder> restored_parts_holder, const MergeTreePartInfo & part_info, const String & part_path_in_backup) const;
    
    virtual void attachRestoredParts(MutableDataPartsVector && parts) = 0;
    static void incrementInsertedPartsProfileEvent(MergeTreeDataPartType type);
    static void incrementMergedPartsProfileEvent(MergeTreeDataPartType type);
private:
    
    void checkPartCanBeAddedToTable(MutableDataPartPtr & part, DataPartsLock & lock) const;
    
    
    void preparePartForCommit(MutableDataPartPtr & part, Transaction & out_transaction, DataPartStorageBuilderPtr builder);