**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 :)

throw Exception(
                    "Trying to ALTER DROP version " + backQuoteIfNeed(command.column_name) + " column",
                    ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
            }
            else if (command.type == AlterCommand::RENAME_COLUMN)
            {
                throw Exception(
                    "Trying to ALTER RENAME version " + backQuoteIfNeed(command.column_name) + " column",
                    ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
            }
        }
        if (command.type == AlterCommand::MODIFY_ORDER_BY && !is_custom_partitioned)
        {
            throw Exception(
                "ALTER MODIFY ORDER BY is not supported for default-partitioned tables created with the old syntax",
                ErrorCodes::BAD_ARGUMENTS);
        }
        if (command.type == AlterCommand::MODIFY_TTL && !is_custom_partitioned)
        {
            throw Exception(
                "ALTER MODIFY TTL is not supported for default-partitioned tables created with the old syntax",
                ErrorCodes::BAD_ARGUMENTS);
        }
        if (command.type == AlterCommand::MODIFY_SAMPLE_BY)
        {
            if (!is_custom_partitioned)
                throw Exception(
                    "ALTER MODIFY SAMPLE BY is not supported for default-partitioned tables created with the old syntax",
                    ErrorCodes::BAD_ARGUMENTS);
            checkSampleExpression(new_metadata, getSettings()->compatibility_allow_sampling_expression_not_in_primary_key,