**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 :)

}
                    }
                }
            }
            for (const auto & [name, emerging_part] : currently_emerging_big_parts)
            {
                /
                if (committed_big_parts_from_partition.find(name) == committed_big_parts_from_partition.end()
                    && part_info.partition_id == emerging_part.partition_id)
                {
                    auto it = disk_occupation.find(emerging_part.disk_name);
                    if (it != disk_occupation.end())
                    {
                        it->second += emerging_part.estimate_bytes;
                        disk_parts_for_logging[emerging_part.disk_name].push_back(
                            formatReadableSizeWithBinarySuffix(emerging_part.estimate_bytes) + " (emerging)");
                    }
                    else
                    {
                        /
                    }
                }
            }
            size_t min_occupation_size = std::numeric_limits<size_t>::max();
            std::vector<String> candidates;
            for (const auto & [disk_name, size] : disk_occupation)
            {
                if (size < min_occupation_size)
                {
                    min_occupation_size = size;