**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 :)

if (has_count)
    {
        for (const auto & part : real_parts)
        {
            auto & column = assert_cast<ColumnAggregateFunction &>(*partition_minmax_count_columns.back());
            insert(column, part->rows_count);
        }
    }
    block.setColumns(std::move(partition_minmax_count_columns));
    Block res;
    for (const auto & name : required_columns)
    {
        if (virtual_columns_block.has(name))
            res.insert(virtual_columns_block.getByName(name));
        else if (block.has(name))
            res.insert(block.getByName(name));
        else if (startsWith(name, "count")) /
        {
            const auto & column = block.getByName("count()");
            res.insert({column.column, column.type, name});
        }
        else
            throw Exception(
                ErrorCodes::LOGICAL_ERROR,
                "Cannot find column {} in minmax_count projection but query analysis still selects this projection. It's a bug",
                name);
    }
    return res;
}
std::optional<ProjectionCandidate> MergeTreeData::getQueryProcessingStageWithAggregateProjection(