**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 :)

{
    old_and_new_names.push_back({old_name, new_name, disk});
}
void MergeTreeData::PartsTemporaryRename::tryRenameAll()
{
    renamed = true;
    for (size_t i = 0; i < old_and_new_names.size(); ++i)
    {
        try
        {
            const auto & [old_name, new_name, disk] = old_and_new_names[i];
            if (old_name.empty() || new_name.empty())
                throw DB::Exception("Empty part name. Most likely it's a bug.", ErrorCodes::LOGICAL_ERROR);
            const auto full_path = fs::path(storage.relative_data_path) / source_dir;
            disk->moveFile(fs::path(full_path) / old_name, fs::path(full_path) / new_name);
        }
        catch (...)
        {
            old_and_new_names.resize(i);
            LOG_WARNING(storage.log, "Cannot rename parts to perform operation on them: {}", getCurrentExceptionMessage(false));
            throw;
        }
    }
}
MergeTreeData::PartsTemporaryRename::~PartsTemporaryRename()