**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 :)

[min_bytes_to_rebalance_partition_over_jbod](const auto & part)
                        {
                            return !(part->isStoredOnDisk() && part->getBytesOnDisk() >= min_bytes_to_rebalance_partition_over_jbod);
                        });
                /
                for (const auto & part : covered_parts)
                    submerging_big_parts_from_partition.insert(part->name);
                for (const auto & part : getDataPartsStateRange(MergeTreeData::DataPartState::Active))
                {
                    if (part->isStoredOnDisk() && part->getBytesOnDisk() >= min_bytes_to_rebalance_partition_over_jbod
                        && part_info.partition_id == part->info.partition_id)
                    {
                        auto name = part->data_part_storage->getDiskName();
                        auto it = disk_occupation.find(name);
                        if (it != disk_occupation.end())
                        {
                            if (submerging_big_parts_from_partition.find(part->name) == submerging_big_parts_from_partition.end())
                            {
                                it->second += part->getBytesOnDisk();
                                disk_parts_for_logging[name].push_back(formatReadableSizeWithBinarySuffix(part->getBytesOnDisk()));
                                committed_big_parts_from_partition.insert(part->name);
                            }
                            else
                            {
                                disk_parts_for_logging[name].push_back(formatReadableSizeWithBinarySuffix(part->getBytesOnDisk()) + " (submerging)");
                            }
                        }
                        else
                        {
                            /