**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 :)

{
    auto lock = (acquired_lock) ? DataPartsLock() : lockParts();
    DataPartsVector res;
    for (const auto & state : affordable_states)
    {
        DataPartStateAndPartitionID state_with_partition{state, partition_id};
        res.insert(res.end(), data_parts_by_state_and_info.lower_bound(state_with_partition), data_parts_by_state_and_info.upper_bound(state_with_partition));
    }
    return res;
}
MergeTreeData::DataPartsVector MergeTreeData::getDataPartsVectorInPartitionForInternalUsage(
    const MergeTreeData::DataPartState & state, const String & partition_id, DataPartsLock * acquired_lock) const
{
    DataPartStateAndPartitionID state_with_partition{state, partition_id};
    auto lock = (acquired_lock) ? DataPartsLock() : lockParts();
    return DataPartsVector(
        data_parts_by_state_and_info.lower_bound(state_with_partition),
        data_parts_by_state_and_info.upper_bound(state_with_partition));
}
MergeTreeData::DataPartsVector MergeTreeData::getVisibleDataPartsVectorInPartitions(ContextPtr local_context, const std::unordered_set<String> & partition_ids) const