**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::atomic_load(&log_name));
        }
        else
        {
            reservation = destination_ptr->reserve(expected_size);
            if (reservation)
                return reservation;
            else
                if (move_ttl_entry->destination_type == DataDestinationType::VOLUME)
                    LOG_WARNING(
                        log,
                        "Would like to reserve space on volume '{}' by TTL rule of table '{}' but there is not enough space",
                        move_ttl_entry->destination_name,
                        *std::atomic_load(&log_name));
                else if (move_ttl_entry->destination_type == DataDestinationType::DISK)
                    LOG_WARNING(
                        log,
                        "Would like to reserve space on disk '{}' by TTL rule of table '{}' but there is not enough space",
                        move_ttl_entry->destination_name,
                        *std::atomic_load(&log_name));
        }
    }
    /
    if (selected_disk)
        reservation = selected_disk->reserve(expected_size);
    if (!reservation)
        reservation = getStoragePolicy()->reserve(expected_size, min_volume_index);
    return reservation;
}
SpacePtr MergeTreeData::getDestinationForMoveTTL(const TTLDescription & move_ttl, bool is_insert) const