**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 (miss_column)
            throw Exception("Version column " + version_column + " does not exist in table declaration.", ErrorCodes::NO_SUCH_COLUMN_IN_TABLE);
    };
    if (mode == MergingParams::Collapsing)
        check_sign_column(false, "CollapsingMergeTree");
    if (mode == MergingParams::Summing)
    {
        
        for (const auto & column_to_sum : columns_to_sum)
        {
            auto check_column_to_sum_exists = [& column_to_sum](const NameAndTypePair & name_and_type)
            {
                return column_to_sum == Nested::extractTableName(name_and_type.name);
            };
            if (columns.end() == std::find_if(columns.begin(), columns.end(), check_column_to_sum_exists))
                throw Exception(
                        "Column " + column_to_sum + " listed in columns to sum does not exist in table declaration.", ErrorCodes::NO_SUCH_COLUMN_IN_TABLE);
        }
        
        if (metadata.isPartitionKeyDefined())
        {
            auto partition_key_columns = metadata.getPartitionKey().column_names;
            Names names_intersection;
            std::set_intersection(columns_to_sum.begin(), columns_to_sum.end(),
                                  partition_key_columns.begin(), partition_key_columns.end(),
                                  std::back_inserter(names_intersection));
            if (!names_intersection.empty())
                throw Exception("Columns: " + boost::algorithm::join(names_intersection, ", ") +
                " listed both in columns to sum and in partition key. That is not allowed.", ErrorCodes::BAD_ARGUMENTS);
        }