**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 :)

{
    return getVisibleDataPartsVectorInPartition(local_context->getCurrentTransaction().get(), partition_id);
}
MergeTreeData::DataPartsVector MergeTreeData::getVisibleDataPartsVectorInPartition(
    ContextPtr local_context, const String & partition_id, DataPartsLock & lock) const
{
    return getVisibleDataPartsVectorInPartition(local_context->getCurrentTransaction().get(), partition_id, &lock);
}
MergeTreeData::DataPartsVector MergeTreeData::getVisibleDataPartsVectorInPartition(
    MergeTreeTransaction * txn, const String & partition_id, DataPartsLock * acquired_lock) const
{
    if (txn)
    {
        DataPartStateAndPartitionID active_parts{MergeTreeDataPartState::Active, partition_id};
        DataPartStateAndPartitionID outdated_parts{MergeTreeDataPartState::Outdated, partition_id};
        DataPartsVector res;
        {
            auto lock = (acquired_lock) ? DataPartsLock() : lockParts();
            res.insert(res.end(), data_parts_by_state_and_info.lower_bound(active_parts), data_parts_by_state_and_info.upper_bound(active_parts));
            res.insert(res.end(), data_parts_by_state_and_info.lower_bound(outdated_parts), data_parts_by_state_and_info.upper_bound(outdated_parts));
        }
        filterVisibleDataParts(res, txn->getSnapshot(), txn->tid);
        return res;
    }
    return getDataPartsVectorInPartitionForInternalUsage(MergeTreeDataPartState::Active, partition_id, acquired_lock);
}
MergeTreeData::DataPartsVector MergeTreeData::getDataPartsVectorInPartitionForInternalUsage(const DataPartStates & affordable_states, const String & partition_id, DataPartsLock * acquired_lock) const