**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 :)

DataPartPtr & out_covering_part,
        DataPartsLock & data_parts_lock) const;
    
    bool isPrimaryOrMinMaxKeyColumnPossiblyWrappedInFunctions(const ASTPtr & node, const StorageMetadataPtr & metadata_snapshot) const;
    
    PartitionCommandsResultInfo freezePartitionsByMatcher(MatcherFn matcher, const StorageMetadataPtr & metadata_snapshot, const String & with_name, ContextPtr context);
    PartitionCommandsResultInfo unfreezePartitionsByMatcher(MatcherFn matcher, const String & backup_name, ContextPtr context);
    
    bool canReplacePartition(const DataPartPtr & src_part) const;
    
    virtual void dropPartNoWaitNoThrow(const String & part_name) = 0;
    virtual void dropPart(const String & part_name, bool detach, ContextPtr context) = 0;
    virtual void dropPartition(const ASTPtr & partition, bool detach, ContextPtr context) = 0;
    virtual PartitionCommandsResultInfo attachPartition(const ASTPtr & partition, const StorageMetadataPtr & metadata_snapshot, bool part, ContextPtr context) = 0;
    virtual void replacePartitionFrom(const StoragePtr & source_table, const ASTPtr & partition, bool replace, ContextPtr context) = 0;
    virtual void movePartitionToTable(const StoragePtr & dest_table, const ASTPtr & partition, ContextPtr context) = 0;
    virtual void fetchPartition(
        const ASTPtr & partition,
        const StorageMetadataPtr & metadata_snapshot,
        const String & from,
        bool fetch_part,
        ContextPtr query_context);
    virtual void movePartitionToShard(const ASTPtr & partition, bool move_part, const String & to, ContextPtr query_context);
    void writePartLog(
        PartLogElement::Type type,
        const ExecutionStatus & execution_status,
        UInt64 elapsed_ns,
        const String & new_part_name,
        const DataPartPtr & result_part,
        const DataPartsVector & source_parts,