**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 :)

candidates = {disk_name};
                }
                else if (size == min_occupation_size)
                {
                    candidates.push_back(disk_name);
                }
            }
            if (!candidates.empty())
            {
                /
                std::shuffle(candidates.begin(), candidates.end(), thread_local_rng);
                String selected_disk_name = candidates.front();
                WriteBufferFromOwnString log_str;
                writeCString("\nbalancer: \n", log_str);
                for (const auto & [disk_name, per_disk_parts] : disk_parts_for_logging)
                    writeString(fmt::format("  {}: [{}]\n", disk_name, fmt::join(per_disk_parts, ", ")), log_str);
                LOG_DEBUG(log, fmt::runtime(log_str.str()));
                if (ttl_infos)
                    reserved_space = tryReserveSpacePreferringTTLRules(
                        metadata_snapshot,
                        part_size,
                        *ttl_infos,
                        time(nullptr),
                        max_volume_index,
                        is_insert,
                        getStoragePolicy()->getDiskByName(selected_disk_name));
                else
                    reserved_space = tryReserveSpace(part_size, getStoragePolicy()->getDiskByName(selected_disk_name));
                if (reserved_space)
                {