**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 :)

currently_emerging_big_parts.emplace(
                        part_name, EmergingPartInfo{reserved_space->getDisk(0)->getName(), part_info.partition_id, part_size});
                    for (const auto & part : covered_parts)
                    {
                        if (currently_submerging_big_parts.contains(part))
                            LOG_WARNING(log, "currently_submerging_big_parts contains duplicates. JBOD might lose balance");
                        else
                            currently_submerging_big_parts.insert(part);
                    }
                    /
                    tagger_ptr->emplace(*this, part_name, std::move(covered_parts), log);
                }
            }
        }
        catch (...)
        {
            LOG_DEBUG(log, "JBOD balancer encounters an error. Fallback to random disk selection");
            tryLogCurrentException(log);
        }
    }
    return reserved_space;
}
ColumnsDescription MergeTreeData::getObjectColumns(
    const DataPartsVector & parts, const ColumnsDescription & storage_columns)
{
    return DB::getObjectColumns(
        parts.begin(), parts.end(),
        storage_columns, [](const auto & part) -> const auto & { return part->getColumns(); });
}
ColumnsDescription MergeTreeData::getObjectColumns(