**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 :)

{
        
        std::string source_table_shared_id;
        
        std::string source_part_name;
        
        NameSet hardlinks_from_source_part;
    };
    std::pair<MergeTreeData::MutableDataPartPtr, scope_guard> cloneAndLoadDataPartOnSameDisk(
        const MergeTreeData::DataPartPtr & src_part, const String & tmp_part_prefix,
        const MergeTreePartInfo & dst_part_info, const StorageMetadataPtr & metadata_snapshot,
        const MergeTreeTransactionPtr & txn, HardlinkedFiles * hardlinked_files,
        bool copy_instead_of_hardlink);
    virtual std::vector<MergeTreeMutationStatus> getMutationsStatus() const = 0;
    
    
    virtual bool canUseAdaptiveGranularity() const
    {
        const auto settings = getSettings();
        return settings->index_granularity_bytes != 0 &&
            (settings->enable_mixed_granularity_parts || !has_non_adaptive_index_granularity_parts);
    }
    
    
    
    MergeTreeSettingsPtr getSettings() const
    {
        return storage_settings.get();
    }
    String getRelativeDataPath() const { return relative_data_path; }