**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 :)

for (const String & disk_name : all_diff_disk_names)
                    {
                        auto disk = new_storage_policy->getDiskByName(disk_name);
                        if (disk->exists(relative_data_path))
                            throw Exception("New storage policy contain disks which already contain data of a table with the same name", ErrorCodes::LOGICAL_ERROR);
                    }
                    for (const String & disk_name : all_diff_disk_names)
                    {
                        auto disk = new_storage_policy->getDiskByName(disk_name);
                        disk->createDirectories(relative_data_path);
                        disk->createDirectories(fs::path(relative_data_path) / MergeTreeData::DETACHED_DIR_NAME);
                    }
                    
                    has_storage_policy_changed = true;
                }
            }
        }
        
        auto copy = getDefaultSettings();
        copy->applyChanges(new_changes);
        copy->sanityCheck(getContext()->getMergeMutateExecutor()->getMaxTasksCount());
        storage_settings.set(std::move(copy));
        StorageInMemoryMetadata new_metadata = getInMemoryMetadata();
        new_metadata.setSettingsChanges(new_settings);
        setInMemoryMetadata(new_metadata);
        if (has_storage_policy_changed)
            startBackgroundMovesIfNeeded();
    }
}
void MergeTreeData::PartsTemporaryRename::addPart(const String & old_name, const String & new_name, const DiskPtr & disk)