**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 dropIfEmpty();
    
    
    
    void rename(const String & new_table_path, const StorageID & new_table_id) override;
    
    void renameInMemory(const StorageID & new_table_id) override;
    
    
    
    
    
    void checkAlterIsPossible(const AlterCommands & commands, ContextPtr context) const override;
    
    
    void checkMutationIsPossible(const MutationCommands & commands, const Settings & settings) const override;
    
    void checkAlterPartitionIsPossible(const PartitionCommands & commands, const StorageMetadataPtr & metadata_snapshot, const Settings & settings) const override;
    
    void changeSettings(
        const ASTPtr & new_settings,
        AlterLockHolder & table_lock_holder);
    
    
    
    void reportBrokenPart(MergeTreeData::DataPartPtr & data_part) const;
    
    
    static ASTPtr extractKeyExpressionList(const ASTPtr & node)