**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 :)

}
            });
        }
        pool.wait();
    }
    else
    {
        for (const DataPartPtr & part : parts_to_remove)
        {
            LOG_DEBUG(log, "Removing part from filesystem {}", part->name);
            part->remove();
            if (part_names_successed)
                part_names_successed->insert(part->name);
        }
    }
}
size_t MergeTreeData::clearOldBrokenPartsFromDetachedDirecory()
{
    /**
     * Remove old (configured by setting) broken detached parts.
     * Only parts with certain prefixes are removed. These prefixes
     * are such that it is guaranteed that they will never be needed
     * and need to be cleared. ctime is used to check when file was
     * moved to detached/ directory (see https:unix.stackexchange.com/a/211134)
     */
    DetachedPartsInfo detached_parts = getDetachedParts();
    if (detached_parts.empty())
        return 0;
    PartsTemporaryRename renamed_parts(*this, "detached/");
    for (const auto & part_info : detached_parts)