**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 :)

PartitionCommandsResultInfo unfreezePartition(
        const ASTPtr & partition,
        const String & backup_name,
        ContextPtr context,
        TableLockHolder & table_lock_holder);
    
    PartitionCommandsResultInfo unfreezeAll(
        const String & backup_name,
        ContextPtr context,
        TableLockHolder & table_lock_holder);
    
    void backupData(BackupEntriesCollector & backup_entries_collector, const String & data_path_in_backup, const std::optional<ASTs> & partitions) override;
    
    void restoreDataFromBackup(RestorerFromBackup & restorer, const String & data_path_in_backup, const std::optional<ASTs> & partitions) override;
    
    bool supportsBackupPartition() const override { return true; }
    
    void movePartitionToDisk(const ASTPtr & partition, const String & name, bool moving_part, ContextPtr context);
    
    void movePartitionToVolume(const ASTPtr & partition, const String & name, bool moving_part, ContextPtr context);
    
    
    
    void checkPartitionCanBeDropped(const ASTPtr & partition, ContextPtr local_context);
    void checkPartCanBeDropped(const String & part_name);
    Pipe alterPartition(
        const StorageMetadataPtr & metadata_snapshot,
        const PartitionCommands & commands,
        ContextPtr query_context) override;
    size_t getColumnCompressedSize(const std::string & name) const