**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 :)

, data_parts_by_state_and_info(data_parts_indexes.get<TagByStateAndInfo>())
    , parts_mover(this)
    , background_operations_assignee(*this, BackgroundJobsAssignee::Type::DataProcessing, getContext())
    , background_moves_assignee(*this, BackgroundJobsAssignee::Type::Moving, getContext())
    , use_metadata_cache(getSettings()->use_metadata_cache)
{
    context_->getGlobalContext()->initializeBackgroundExecutorsIfNeeded();
    const auto settings = getSettings();
    allow_nullable_key = attach || settings->allow_nullable_key;
    if (relative_data_path.empty())
        throw Exception("MergeTree storages require data path", ErrorCodes::INCORRECT_FILE_NAME);
    
    if (!attach)
        settings->sanityCheck(getContext()->getMergeMutateExecutor()->getMaxTasksCount());
    MergeTreeDataFormatVersion min_format_version(0);
    if (!date_column_name.empty())
    {
        try
        {
            checkPartitionKeyAndInitMinMax(metadata_.partition_key);
            setProperties(metadata_, metadata_, attach);
            if (minmax_idx_date_column_pos == -1)
                throw Exception("Could not find Date column", ErrorCodes::BAD_TYPE_OF_FIELD);
        }
        catch (Exception & e)
        {
            
            e.addMessage("(while initializing MergeTree partition key from date column " + backQuote(date_column_name) + ")");
            throw;
        }