**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 :)

auto load_part = [&](const String & part_name, const DiskPtr & part_disk_ptr)
    {
        auto part_opt = MergeTreePartInfo::tryParsePartName(part_name, format_version);
        if (!part_opt)
            return;
        const auto & part_info = *part_opt;
        auto single_disk_volume = std::make_shared<SingleDiskVolume>("volume_" + part_name, part_disk_ptr, 0);
        auto data_part_storage = std::make_shared<DataPartStorageOnDisk>(single_disk_volume, relative_data_path, part_name);
        auto part = createPart(part_name, part_info, data_part_storage);
        bool broken = false;
        String part_path = fs::path(relative_data_path) / part_name;
        String marker_path = fs::path(part_path) / IMergeTreeDataPart::DELETE_ON_DESTROY_MARKER_FILE_NAME;
        if (part_disk_ptr->exists(marker_path))
        {
            
            size_t size_of_part = data_part_storage->calculateTotalSizeOnDisk();
            LOG_WARNING(log,
                "Detaching stale part {}{} (size: {}), which should have been deleted after a move. "
                "That can only happen after unclean restart of ClickHouse after move of a part having an operation blocking that stale copy of part.",
                getFullPathOnDisk(part_disk_ptr), part_name, formatReadableSizeWithBinarySuffix(size_of_part));
            std::lock_guard loading_lock(mutex);
            broken_parts_to_detach.push_back(part);
            ++suspicious_broken_parts;
            suspicious_broken_parts_bytes += size_of_part;
            return;
        }
        try
        {
            part->loadColumnsChecksumsIndexes(require_part_metadata, true);
        }