**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 & part_info : detached_parts)
        {
            LOG_DEBUG(log, "Found part {}", part_info.dir_name);
            active_parts.add(part_info.dir_name);
        }
        LOG_DEBUG(log, "{} of them are active", active_parts.size());
        /
        for (const auto & part_info : detached_parts)
        {
            const String containing_part = active_parts.getContainingPart(part_info.dir_name);
            if (!containing_part.empty() && containing_part != part_info.dir_name)
                part_info.disk->moveDirectory(fs::path(relative_data_path) / source_dir / part_info.dir_name,
                    fs::path(relative_data_path) / source_dir / ("inactive_" + part_info.dir_name));
            else
                renamed_parts.addPart(part_info.dir_name, "attaching_" + part_info.dir_name, part_info.disk);
        }
    }
    /
    renamed_parts.tryRenameAll();
    /
    LOG_DEBUG(log, "Checking parts");
    MutableDataPartsVector loaded_parts;
    loaded_parts.reserve(renamed_parts.old_and_new_names.size());
    for (const auto & [old_name, new_name, disk] : renamed_parts.old_and_new_names)
    {
        LOG_DEBUG(log, "Checking part {}", new_name);
        auto single_disk_volume = std::make_shared<SingleDiskVolume>("volume_" + old_name, disk);
        auto data_part_storage = std::make_shared<DataPartStorageOnDisk>(single_disk_volume, relative_data_path, source_dir + new_name);
        MutableDataPartPtr part = createPart(old_name, data_part_storage);
        loadPartAndFixMetadataImpl(part);