**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 ((*it)->info.min_block < pos)
                continue;
            if (!is_appropriate_state((*it)->getState()))
            {
                update_error(it);
                continue;
            }
            if ((*it)->info.min_block > pos)
                update_error(it);
            if ((*it)->getState() != DataPartState::Active)
                activate_part(it);
            pos = (*it)->info.max_block + 1;
            restored.push_back((*it)->name);
        }
        if (pos != part->info.max_block + 1)
            error = true;
        for (const String & name : restored)
        {
            LOG_INFO(log, "Activated part {}", name);
        }
        if (error)
        {
            LOG_ERROR(log, "The set of parts restored in place of {} looks incomplete. There might or might not be a data loss.{}", part->name, (error_parts.empty() ? "" : " Suspicious parts: " + error_parts));
        }
    }
    if (removed_active_part || restored_active_part)
        resetObjectColumnsFromActiveParts(lock);
}
void MergeTreeData::tryRemovePartImmediately(DataPartPtr && part)