**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 <Storages/MergeTree/MergeTreeData.h>
#include <Backups/BackupEntriesCollector.h>
#include <Backups/BackupEntryFromImmutableFile.h>
#include <Backups/BackupEntryFromSmallFile.h>
#include <Backups/IBackup.h>
#include <Backups/RestorerFromBackup.h>
#include <Compression/CompressedReadBuffer.h>
#include <DataTypes/DataTypeArray.h>
#include <DataTypes/DataTypeDate.h>
#include <DataTypes/DataTypeDateTime.h>
#include <DataTypes/DataTypeEnum.h>
#include <DataTypes/DataTypeLowCardinality.h>
#include <DataTypes/DataTypeNullable.h>
#include <DataTypes/DataTypeUUID.h>
#include <DataTypes/DataTypeTuple.h>
#include <DataTypes/NestedUtils.h>
#include <DataTypes/DataTypeObject.h>
#include <DataTypes/ObjectUtils.h>
#include <Columns/ColumnObject.h>
#include <DataTypes/hasNullable.h>
#include <Disks/ObjectStorages/DiskObjectStorage.h>
#include <Functions/FunctionFactory.h>
#include <Functions/IFunction.h>