**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 :)

#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypesNumber.h>
#include <Processors/Merges/Algorithms/Graphite.h>
#include <Storages/MergeTree/BackgroundJobsAssignee.h>
#include <Storages/MergeTree/MergeTreeIndices.h>
#include <Storages/MergeTree/MergeTreePartInfo.h>
#include <Storages/MergeTree/MergeTreeSettings.h>
#include <Storages/MergeTree/MergeTreeMutationStatus.h>
#include <Storages/MergeTree/MergeList.h>
#include <Storages/MergeTree/IMergeTreeDataPart.h>
#include <Storages/MergeTree/MergeTreeDataPartInMemory.h>
#include <Storages/MergeTree/MergeTreePartsMover.h>
#include <Storages/MergeTree/MergeTreeWriteAheadLog.h>
#include <Storages/MergeTree/PinnedPartUUIDs.h>
#include <Storages/MergeTree/ZeroCopyLock.h>
#include <Storages/MergeTree/TemporaryParts.h>
#include <Storages/IndicesDescription.h>
#include <Storages/DataDestinationType.h>
#include <Storages/extractKeyExpressionList.h>
#include <Storages/PartitionCommands.h>
#include <Interpreters/PartLog.h>
#include <Disks/StoragePolicy.h>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/global_fun.hpp>
#include <boost/range/iterator_range_core.hpp>
namespace DB
{
const size_t DEFAULT_DELAYED_STREAMS_FOR_PARALLEL_WRITE = 1000;
class AlterCommands;