**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 :)

catch (const Exception & e)
        {
            
            
            
            if (isNotEnoughMemoryErrorCode(e.code()))
                throw;
            broken = true;
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }
        catch (...)
        {
            broken = true;
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }
        
        if (broken)
        {
            
            size_t size_of_part = data_part_storage->calculateTotalSizeOnDisk();
            LOG_ERROR(log,
                "Detaching broken part {}{} (size: {}). "
                "If it happened after update, it is likely because of backward incompability. "
                "You need to resolve this manually",
                getFullPathOnDisk(part_disk_ptr), part_name, formatReadableSizeWithBinarySuffix(size_of_part));
            std::lock_guard loading_lock(mutex);
            broken_parts_to_detach.push_back(part);
            ++suspicious_broken_parts;
            suspicious_broken_parts_bytes += size_of_part;
            return;