**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 :)

virtual std::pair<bool, NameSet> unlockSharedData(const IMergeTreeDataPart &) const { return std::make_pair(true, NameSet{}); }
    
    
    virtual DataPartStoragePtr tryToFetchIfShared(const IMergeTreeDataPart &, const DiskPtr &, const String &) { return nullptr; }
    
    
    virtual bool removeDetachedPart(DiskPtr disk, const String & path, const String & part_name, bool is_freezed);
    virtual String getTableSharedID() const { return ""; }
    
    
    virtual void createAndStoreFreezeMetadata(DiskPtr disk, DataPartPtr part, String backup_part_path) const;
    
    
    
    DataParts currently_submerging_big_parts;
    std::map<String, EmergingPartInfo> currently_emerging_big_parts;
    
    mutable std::mutex currently_submerging_emerging_mutex;
    
    using MatcherFn = std::function<bool(const String &)>;
    
    scope_guard getTemporaryPartDirectoryHolder(const String & part_dir_name);
protected:
    friend class IMergeTreeDataPart;
    friend class MergeTreeDataMergerMutator;
    friend struct ReplicatedMergeTreeTableMetadata;
    friend class StorageReplicatedMergeTree;