**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 :)

candidate.prewhere_info->prewhere_actions = prewhere_actions;
            }
            if (candidate.prewhere_info->row_level_filter)
            {
                auto row_level_filter_actions = candidate.prewhere_info->row_level_filter->clone();
                /
                auto new_prewhere_required_columns = row_level_filter_actions->foldActionsByProjection(
                    prewhere_required_columns, projection.sample_block_for_keys, candidate.prewhere_info->row_level_column_name, false);
                if (new_prewhere_required_columns.empty() && !prewhere_required_columns.empty())
                    return false;
                prewhere_required_columns = std::move(new_prewhere_required_columns);
                candidate.prewhere_info->row_level_filter = row_level_filter_actions;
            }
            required_columns.insert(prewhere_required_columns.begin(), prewhere_required_columns.end());
        }
        bool match = true;
        for (const auto & column : required_columns)
        {
            /
            if (!source_block.has(column))
            {
                match = false;
                break;
            }
        }
        return match;
    };
    auto virtual_block = getSampleBlockWithVirtualColumns();
    auto add_projection_candidate = [&](const ProjectionDescription & projection, bool minmax_count_projection = false)
    {