**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 (expr.hasArrayJoin())
        throw Exception(key_name + " key cannot contain array joins", ErrorCodes::ILLEGAL_COLUMN);
    try
    {
        expr.assertDeterministic();
    }
    catch (Exception & e)
    {
        e.addMessage(fmt::format("for {} key", key_name));
        throw;
    }
    for (const ColumnWithTypeAndName & element : sample_block)
    {
        const ColumnPtr & column = element.column;
        if (column && (isColumnConst(*column) || column->isDummy()))
            throw Exception(ErrorCodes::ILLEGAL_COLUMN, "{} key cannot contain constants", key_name);
        if (!allow_nullable_key && hasNullable(element.type))
            throw Exception(
                ErrorCodes::ILLEGAL_COLUMN, "{} key contains nullable columns, but merge tree setting `allow_nullable_key` is disabled", key_name);
    }
}
void MergeTreeData::checkProperties(