**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 :)

ProjectionCandidate candidate{};
        candidate.desc = &projection;
        auto sample_block = projection.sample_block;
        auto sample_block_for_keys = projection.sample_block_for_keys;
        for (const auto & column : virtual_block)
        {
            sample_block.insertUnique(column);
            sample_block_for_keys.insertUnique(column);
        }
        /
        auto attach_aggregation_in_order_info = [&]()
        {
            for (const auto & desc : select.getQueryAnalyzer()->aggregationKeys())
            {
                const String & key = desc.name;
                auto actions_dag = analysis_result.before_aggregation->clone();
                actions_dag->foldActionsByProjection({key}, sample_block_for_keys);
                candidate.group_by_elements_actions.emplace_back(std::make_shared<ExpressionActions>(actions_dag, actions_settings));
                candidate.group_by_elements_order_descr.emplace_back(key, 1, 1);
            }
        };
        if (projection.type == ProjectionDescription::Type::Aggregate && analysis_result.need_aggregate && can_use_aggregate_projection)
        {
            Block aggregates;
            /
            for (const auto & aggregate : select.getQueryAnalyzer()->aggregates())
            {
                if (const auto * column = sample_block.findByName(aggregate.column_name))
                {
                    aggregates.insert(*column);