**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 :)

part_log->add(part_log_elem);
}
catch (...)
{
    tryLogCurrentException(log, __PRETTY_FUNCTION__);
}
StorageMergeTree::PinnedPartUUIDsPtr MergeTreeData::getPinnedPartUUIDs() const
{
    std::lock_guard lock(pinned_part_uuids_mutex);
    return pinned_part_uuids;
}
MergeTreeData::CurrentlyMovingPartsTagger::CurrentlyMovingPartsTagger(MergeTreeMovingParts && moving_parts_, MergeTreeData & data_)
    : parts_to_move(std::move(moving_parts_)), data(data_)
{
    for (const auto & moving_part : parts_to_move)
        if (!data.currently_moving_parts.emplace(moving_part.part).second)
            throw Exception("Cannot move part '" + moving_part.part->name + "'. It's already moving.", ErrorCodes::LOGICAL_ERROR);
}
MergeTreeData::CurrentlyMovingPartsTagger::~CurrentlyMovingPartsTagger()
{
    std::lock_guard lock(data.moving_parts_mutex);
    for (const auto & moving_part : parts_to_move)
    {
        /
        if (!data.currently_moving_parts.contains(moving_part.part))
            std::terminate();
        data.currently_moving_parts.erase(moving_part.part);
    }
}
bool MergeTreeData::scheduleDataMovingJob(BackgroundJobsAssignee & assignee)