**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 RENAME key " + backQuoteIfNeed(command.column_name) + " column which is a part of key expression",
                    ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
            }
        }
        else if (command.type == AlterCommand::DROP_COLUMN)
        {
            if (columns_in_keys.contains(command.column_name))
            {
                throw Exception(
                    "Trying to ALTER DROP key " + backQuoteIfNeed(command.column_name) + " column which is a part of key expression",
                    ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
            }
            if (!command.clear)
            {
                const auto & deps_mv = name_deps[command.column_name];
                if (!deps_mv.empty())
                {
                    throw Exception(
                        "Trying to ALTER DROP column " + backQuoteIfNeed(command.column_name) + " which is referenced by materialized view "
                            + toString(deps_mv),
                        ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
                }
            }
            dropped_columns.emplace(command.column_name);
        }
        else if (command.type == AlterCommand::RESET_SETTING)
        {
            for (const auto & reset_setting : command.settings_resets)