**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 (parts_mover.moves_blocker.isCancelled())
        return false;
    auto moving_tagger = selectPartsForMove();
    if (moving_tagger->parts_to_move.empty())
        return false;
    assignee.scheduleMoveTask(std::make_shared<ExecutableLambdaAdapter>(
        [this, moving_tagger] () mutable
        {
            return moveParts(moving_tagger);
        }, moves_assignee_trigger, getStorageID()));
    return true;
}
bool MergeTreeData::areBackgroundMovesNeeded() const
{
    auto policy = getStoragePolicy();
    if (policy->getVolumes().size() > 1)
        return true;
    return policy->getVolumes().size() == 1 && policy->getVolumes()[0]->getDisks().size() > 1;
}
bool MergeTreeData::movePartsToSpace(const DataPartsVector & parts, SpacePtr space)