**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 :)

{
    precommitted_parts.insert(part);
    part_builders.push_back(builder);
}
void MergeTreeData::Transaction::rollback()
{
    if (!isEmpty())
    {
        WriteBufferFromOwnString buf;
        buf << " Removing parts:";
        for (const auto & part : precommitted_parts)
            buf << " " << part->data_part_storage->getPartDirectory();
        buf << ".";
        LOG_DEBUG(data.log, "Undoing transaction.{}", buf.str());
        data.removePartsFromWorkingSet(txn,
            DataPartsVector(precommitted_parts.begin(), precommitted_parts.end()),
            / true);
    }
    clear();
}
MergeTreeData::DataPartsVector MergeTreeData::Transaction::commit(MergeTreeData::DataPartsLock * acquired_parts_lock)