**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 (!new_type->canBeUsedAsVersion())
        throw Exception("Cannot alter version column " + backQuoteIfNeed(column_name) +
            " to type " + new_type->getName() +
            " because version column must be of an integer type or of type Date or DateTime"
            , ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
    auto which_new_type = WhichDataType(new_type);
    auto which_old_type = WhichDataType(old_type);
    
    if ((which_old_type.isInt() && !which_new_type.isInt())
        || (which_old_type.isUInt() && !which_new_type.isUInt())
        || (which_old_type.isDate() && !which_new_type.isDate())
        || (which_old_type.isDate32() && !which_new_type.isDate32())
        || (which_old_type.isDateTime() && !which_new_type.isDateTime())
        || (which_old_type.isFloat() && !which_new_type.isFloat()))
    {
        throw Exception("Cannot alter version column " + backQuoteIfNeed(column_name) +
            " from type " + old_type->getName() +
            " to type " + new_type->getName() + " because new type will change sort order of version column." +
            " The only possible conversion is expansion of the number of bytes of the current type."
            , ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
    }
    
    if (new_type->getSizeOfValueInMemory() < old_type->getSizeOfValueInMemory())
    {
        throw Exception("Cannot alter version column " + backQuoteIfNeed(column_name) +
            " from type " + old_type->getName() +
            " to type " + new_type->getName() + " because new type is smaller than current in the number of bytes." +
            " The only possible conversion is expansion of the number of bytes of the current type."