**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/checkDataPart.h>
#include <Storages/MergeTree/localBackup.h>
#include <Storages/StorageMergeTree.h>
#include <Storages/StorageReplicatedMergeTree.h>
#include <Storages/VirtualColumnUtils.h>
#include <Storages/Freeze.h>
#include <Common/Increment.h>
#include <Common/SimpleIncrement.h>
#include <Common/Stopwatch.h>
#include <Common/StringUtils/StringUtils.h>
#include <Disks/TemporaryFileOnDisk.h>
#include <Common/escapeForFileName.h>
#include <Common/quoteString.h>
#include <Common/typeid_cast.h>
#include <Common/noexcept_scope.h>
#include <Processors/QueryPlan/ReadFromMergeTree.h>
#include <Processors/Formats/IInputFormat.h>
#include <AggregateFunctions/AggregateFunctionCount.h>
#include <boost/range/adaptor/filtered.hpp>
#include <boost/range/algorithm_ext/erase.hpp>
#include <boost/algorithm/string/join.hpp>
#include <boost/algorithm/string/replace.hpp>
#include <base/insertAtEnd.h>
#include <base/sort.h>
#include <algorithm>
#include <iomanip>
#include <optional>
#include <set>
#include <thread>
#include <typeinfo>