**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 normal_result_ptr = reader.estimateNumMarksToRead(
            normal_parts,
            required_columns,
            storage_snapshot->metadata,
            storage_snapshot->metadata,
            query_info, /
            added_filter_nodes,
            query_context,
            settings.max_threads,
            max_added_blocks);
        if (normal_result_ptr->error())
            return;
        if (normal_result_ptr->marks() == 0)
            candidate.complete = true;
        else
        {
            sum_marks += normal_result_ptr->marks();
            candidate.merge_tree_normal_select_result_ptr = normal_result_ptr;
        }
    }
    candidate.merge_tree_projection_select_result_ptr = projection_result_ptr;
    /
    if (sum_marks < min_sum_marks)
    {
        selected_candidate = &candidate;
        min_sum_marks = sum_marks;
    }
}
Block MergeTreeData::getMinMaxCountProjectionBlock(