**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 :)

{
    column_sizes.clear();
    
    auto committed_parts_range = getDataPartsStateRange(DataPartState::Active);
    for (const auto & part : committed_parts_range)
        addPartContributionToColumnAndSecondaryIndexSizes(part);
}
void MergeTreeData::addPartContributionToColumnAndSecondaryIndexSizes(const DataPartPtr & part)
{
    for (const auto & column : part->getColumns())
    {
        ColumnSize & total_column_size = column_sizes[column.name];
        ColumnSize part_column_size = part->getColumnSize(column.name);
        total_column_size.add(part_column_size);
    }
    auto indexes_descriptions = getInMemoryMetadataPtr()->secondary_indices;
    for (const auto & index : indexes_descriptions)
    {
        IndexSize & total_secondary_index_size = secondary_index_sizes[index.name];
        IndexSize part_index_size = part->getSecondaryIndexSize(index.name);
        total_secondary_index_size.add(part_index_size);
    }
}
void MergeTreeData::removePartContributionToColumnAndSecondaryIndexSizes(const DataPartPtr & part)
{
    for (const auto & column : part->getColumns())
    {
        ColumnSize & total_column_size = column_sizes[column.name];
        ColumnSize part_column_size = part->getColumnSize(column.name);
        auto log_subtract = [&](size_t & from, size_t value, const char * field)