**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 :)

{
    
    if (!renamed)
        return;
    for (const auto & [old_name, new_name, disk] : old_and_new_names)
    {
        if (old_name.empty())
            continue;
        try
        {
            const String full_path = fs::path(storage.relative_data_path) / source_dir;
            disk->moveFile(fs::path(full_path) / new_name, fs::path(full_path) / old_name);
        }
        catch (...)
        {
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }
    }
}
MergeTreeData::DataPartsVector MergeTreeData::getActivePartsToReplace(