**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 :)

{
    NameSet part_names_successeded;
    auto get_failed_parts = [&part_names_successeded, &parts_failed_to_delete, &parts] ()
    {
        if (part_names_successeded.size() == parts.size())
            return;
        if (parts_failed_to_delete)
        {
            for (const auto & part : parts)
            {
                if (!part_names_successeded.contains(part->name))
                    parts_failed_to_delete->insert(part->name);
            }
        }
    };
    try
    {
        clearPartsFromFilesystemImpl(parts, &part_names_successeded);
        get_failed_parts();
    }
    catch (...)
    {
        get_failed_parts();
        if (throw_on_error)
            throw;
    }
}
void MergeTreeData::clearPartsFromFilesystemImpl(const DataPartsVector & parts_to_remove, NameSet * part_names_successed)