**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 :)

if (!new_part_info.isDisjoint((*prev)->info))
                throw Exception(ErrorCodes::LOGICAL_ERROR, "Part {} intersects previous part {}. It is a bug.",
                                new_part_name, (*prev)->getNameWithState());
            break;
        }
        begin = prev;
    }
    
    DataPartIteratorByStateAndInfo end = it_middle;
    while (end != committed_parts_range.end())
    {
        if ((*end)->info == new_part_info)
            throw Exception(ErrorCodes::LOGICAL_ERROR, "Unexpected duplicate part {}. It is a bug.", (*end)->getNameWithState());
        if (!new_part_info.contains((*end)->info))
        {
            if ((*end)->info.contains(new_part_info))
            {
                out_covering_part = *end;
                return {};
            }
            if (!new_part_info.isDisjoint((*end)->info))
                throw Exception(ErrorCodes::LOGICAL_ERROR, "Part {} intersects next part {}. It is a bug.",
                                new_part_name, (*end)->getNameWithState());
            break;
        }
        ++end;
    }
    return DataPartsVector{begin, end};
}
bool MergeTreeData::renameTempPartAndAdd(