**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 (!getStorageID().hasUUID())
        getContext()->dropCaches();
    LOG_TRACE(log, "dropAllData: removing data from filesystem.");
    
    clearPartsFromFilesystem(all_parts);
    for (const auto & disk : getDisks())
    {
        if (disk->isBroken())
            continue;
        try
        {
            disk->removeRecursive(relative_data_path);
        }
        catch (const fs::filesystem_error & e)
        {
            if (e.code() == std::errc::no_such_file_or_directory)
            {
                
                tryLogCurrentException(__PRETTY_FUNCTION__);
            }
            else
                throw;
        }
    }
    setDataVolume(0, 0, 0);
    LOG_TRACE(log, "dropAllData: done.");
}
void MergeTreeData::dropIfEmpty()