**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 :)

{
        DataPartState state;
        String partition_id;
    };
    STRONG_TYPEDEF(String, PartitionID)
    
    
    
    
    
    struct AlterConversions
    {
        
        std::unordered_map<String, String> rename_map;
        bool isColumnRenamed(const String & new_name) const { return rename_map.count(new_name) > 0; }
        String getColumnOldName(const String & new_name) const { return rename_map.at(new_name); }
    };
    struct LessDataPart
    {
        using is_transparent = void;
        bool operator()(const DataPartPtr & lhs, const MergeTreePartInfo & rhs) const { return lhs->info < rhs; }
        bool operator()(const MergeTreePartInfo & lhs, const DataPartPtr & rhs) const { return lhs < rhs->info; }
        bool operator()(const DataPartPtr & lhs, const DataPartPtr & rhs) const { return lhs->info < rhs->info; }
        bool operator()(const MergeTreePartInfo & lhs, const PartitionID & rhs) const { return lhs.partition_id < rhs.toUnderType(); }
        bool operator()(const PartitionID & lhs, const MergeTreePartInfo & rhs) const { return lhs.toUnderType() < rhs.partition_id; }
    };
    struct LessStateDataPart
    {
        using is_transparent = void;
        bool operator() (const DataPartStateAndInfo & lhs, const DataPartStateAndInfo & rhs) const