**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 (prefix.empty())
        LOG_INFO(log, "Renaming {} to {} and forgetting it.", part_to_detach->data_part_storage->getPartDirectory(), part_to_detach->name);
    else
        LOG_INFO(log, "Renaming {} to {}_{} and forgetting it.", part_to_detach->data_part_storage->getPartDirectory(), prefix, part_to_detach->name);
    auto lock = lockParts();
    bool removed_active_part = false;
    bool restored_active_part = false;
    auto it_part = data_parts_by_info.find(part_to_detach->info);
    if (it_part == data_parts_by_info.end())
        throw Exception("No such data part " + part_to_detach->getNameWithState(), ErrorCodes::NO_SUCH_DATA_PART);
    
    
    
    DataPartPtr part = *it_part; 
    if (part->getState() == DataPartState::Active)
    {
        removePartContributionToDataVolume(part);
        removePartContributionToColumnAndSecondaryIndexSizes(part);
        removed_active_part = true;
    }
    modifyPartState(it_part, DataPartState::Deleting);
    auto builder = part->data_part_storage->getBuilder();
    part->renameToDetached(prefix, builder);
    builder->commit();