**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 :)

void forgetPartAndMoveToDetached(const DataPartPtr & part, const String & prefix = "", bool restore_covered = false);
    
    void tryRemovePartImmediately(DataPartPtr && part);
    
    
    DataPartsVector grabOldParts(bool force = false);
    
    void rollbackDeletingParts(const DataPartsVector & parts);
    
    void removePartsFinally(const DataPartsVector & parts);
    
    void flushAllInMemoryPartsIfNeeded();
    
    
    size_t clearOldPartsFromFilesystem(bool force = false);
    
    void clearPartsFromFilesystem(const DataPartsVector & parts, bool throw_on_error = true, NameSet * parts_failed_to_delete = nullptr);
    
    size_t clearOldWriteAheadLogs();
    size_t clearOldBrokenPartsFromDetachedDirecory();
    
    
    size_t clearOldTemporaryDirectories(size_t custom_directories_lifetime_seconds, const NameSet & valid_prefixes = {"tmp_", "tmp-fetch_"});
    size_t clearEmptyParts();
    
    
    void dropAllData();