**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 sum_marks = query_info.merge_tree_select_result_ptr->marks() + 1;
            if (sum_marks < min_sum_marks)
            {
                selected_candidate = nullptr;
                min_sum_marks = sum_marks;
            }
        }
        /
        for (auto & candidate : candidates)
        {
            if (candidate.desc->type == ProjectionDescription::Type::Aggregate)
            {
                selectBestProjection(
                    reader,
                    storage_snapshot,
                    query_info,
                    added_filter_nodes,
                    analysis_result.required_columns,
                    candidate,
                    query_context,
                    max_added_blocks,
                    settings,
                    parts,
                    selected_candidate,
                    min_sum_marks);
            }
        }