**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 :)

{
    auto policy = getStoragePolicy();
    if (move_ttl.destination_type == DataDestinationType::VOLUME)
    {
        auto volume = policy->tryGetVolumeByName(move_ttl.destination_name);
        if (!volume)
            return {};
        if (is_insert && !volume->perform_ttl_move_on_insert)
            return {};
        return volume;
    }
    else if (move_ttl.destination_type == DataDestinationType::DISK)
    {
        auto disk = policy->tryGetDiskByName(move_ttl.destination_name);
        if (!disk)
            return {};
        auto volume = policy->getVolume(policy->getVolumeIndexByDisk(disk));
        if (!volume)
            return {};
        if (is_insert && !volume->perform_ttl_move_on_insert)
            return {};
        return disk;
    }
    else
        return {};
}
bool MergeTreeData::isPartInTTLDestination(const TTLDescription & ttl, const IMergeTreeDataPart & part) const