**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 (!part.unique())
            {
                skipped_parts.push_back(part->info);
                continue;
            }
            if ((part_remove_time < now && now - part_remove_time > getSettings()->old_parts_lifetime.totalSeconds() && !has_skipped_mutation_parent(part))
                || force
                || isInMemoryPart(part)     
                || (part->version.creation_csn == Tx::RolledBackCSN && getSettings()->remove_rolled_back_parts_immediately))
            {
                parts_to_delete.emplace_back(it);
            }
            else
            {
                skipped_parts.push_back(part->info);
            }
        }
        res.reserve(parts_to_delete.size());
        for (const auto & it_to_delete : parts_to_delete)
        {
            res.emplace_back(*it_to_delete);
            modifyPartState(it_to_delete, DataPartState::Deleting);
        }
    }
    if (!res.empty())
        LOG_TRACE(log, "Found {} old parts to remove.", res.size());
    return res;
}
void MergeTreeData::rollbackDeletingParts(const MergeTreeData::DataPartsVector & parts)