**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 :)

reduce_bytes += covered_part->getBytesOnDisk();
                        reduce_rows += covered_part->rows_count;
                        data.modifyPartState(covered_part, DataPartState::Outdated);
                        data.removePartContributionToColumnAndSecondaryIndexSizes(covered_part);
                    }
                    reduce_parts += covered_parts.size();
                    add_bytes += part->getBytesOnDisk();
                    add_rows += part->rows_count;
                    ++add_parts;
                    data.modifyPartState(part, DataPartState::Active);
                    data.addPartContributionToColumnAndSecondaryIndexSizes(part);
                }
            }
            if (reduce_parts == 0)
            {
                for (const auto & part : precommitted_parts)
                    data.updateObjectColumns(part, parts_lock);
            }
            else
                data.resetObjectColumnsFromActiveParts(parts_lock);
            ssize_t diff_bytes = add_bytes - reduce_bytes;
            ssize_t diff_rows = add_rows - reduce_rows;
            ssize_t diff_parts  = add_parts - reduce_parts;
            data.increaseDataVolume(diff_bytes, diff_rows, diff_parts);
        });
    }
    clear();
    return total_covered_parts;
}
bool MergeTreeData::isPrimaryOrMinMaxKeyColumnPossiblyWrappedInFunctions(