**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 :)

{
    std::lock_guard moving_lock(moving_parts_mutex);
    MergeTreeMovingParts parts_to_move;
    for (const auto & part : parts)
    {
        auto reservation = space->reserve(part->getBytesOnDisk());
        if (!reservation)
            throw Exception("Move is not possible. Not enough space on '" + space->getName() + "'", ErrorCodes::NOT_ENOUGH_SPACE);
        auto reserved_disk = reservation->getDisk();
        if (reserved_disk->exists(relative_data_path + part->name))
            throw Exception(
                "Move is not possible: " + fullPath(reserved_disk, relative_data_path + part->name) + " already exists",
                ErrorCodes::DIRECTORY_ALREADY_EXISTS);
        if (currently_moving_parts.contains(part) || partIsAssignedToBackgroundOperation(part))
            throw Exception(
                "Cannot move part '" + part->name + "' because it's participating in background process",
                ErrorCodes::PART_IS_TEMPORARILY_LOCKED);
        parts_to_move.emplace_back(part, std::move(reservation));
    }
    return std::make_shared<CurrentlyMovingPartsTagger>(std::move(parts_to_move), *this);
}
bool MergeTreeData::moveParts(const CurrentlyMovingPartsTaggerPtr & moving_tagger)