**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 * place = arena.alignedAlloc(size_of_state, align_of_state);
        func->create(place);
        if (const AggregateFunctionCount * agg_count = typeid_cast<const AggregateFunctionCount *>(func.get()))
            agg_count->set(place, value.get<UInt64>());
        else
        {
            auto value_column = func->getReturnType()->createColumnConst(1, value)->convertToFullColumnIfConst();
            const auto * value_column_ptr = value_column.get();
            func->add(place, &value_column_ptr, 0, &arena);
        }
        column.insertFrom(place);
    };
    Block virtual_columns_block;
    auto virtual_block = getSampleBlockWithVirtualColumns();
    bool has_virtual_column = std::any_of(required_columns.begin(), required_columns.end(), [&](const auto & name) { return virtual_block.has(name); });
    if (has_virtual_column || has_filter)
    {
        virtual_columns_block = getBlockWithVirtualPartColumns(parts, false , true /;
        if (virtual_columns_block.rows() == 0)
            return {};
    }
    size_t rows = parts.size();
    ColumnPtr part_name_column;
    std::optional<PartitionPruner> partition_pruner;
    std::optional<KeyCondition> minmax_idx_condition;
    DataTypes minmax_columns_types;
    if (has_filter)
    {
        if (metadata_snapshot->hasPartitionKey())
        {