**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 (!it->unique())
                    LOG_WARNING(log, "Cannot immediately remove part {} because someone using it right now "
                             "usage counter {}", part_name_with_state, it->use_count());
                return;
            }
            modifyPartState(it, DataPartState::Deleting);
            part_to_delete = *it;
        }
        else
        {
            part_to_delete = std::move(part);
        }
    }
    try
    {
        part_to_delete->remove();
    }
    catch (...)
    {
        rollbackDeletingParts({part_to_delete});
        throw;
    }
    removePartsFinally({part_to_delete});
    LOG_TRACE(log, "Removed part {}", part_to_delete->name);
}
size_t MergeTreeData::getTotalActiveSizeInBytes() const
{
    return total_active_size_bytes.load(std::memory_order_acquire);
}
size_t MergeTreeData::getTotalActiveSizeInRows() const