**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 :)

{
        auto lock = lockParts();
        const auto it = column_sizes.find(name);
        return it == std::end(column_sizes) ? 0 : it->second.data_compressed;
    }
    ColumnSizeByName getColumnSizes() const override
    {
        auto lock = lockParts();
        return column_sizes;
    }
    const ColumnsDescription & getObjectColumns() const { return object_columns; }
    
    static ColumnsDescription getObjectColumns(
        const DataPartsVector & parts, const ColumnsDescription & storage_columns);
    IndexSizeByName getSecondaryIndexSizes() const override
    {
        auto lock = lockParts();
        return secondary_index_sizes;
    }
    
    String getPartitionIDFromQuery(const ASTPtr & ast, ContextPtr context, DataPartsLock * acquired_lock = nullptr) const;
    std::unordered_set<String> getPartitionIDsFromQuery(const ASTs & asts, ContextPtr context) const;
    std::set<String> getPartitionIdsAffectedByCommands(const MutationCommands & commands, ContextPtr query_context) const;
    
    
    
    MergeTreeData & checkStructureAndGetMergeTreeData(const StoragePtr & source_table, const StorageMetadataPtr & src_snapshot, const StorageMetadataPtr & my_snapshot) const;
    MergeTreeData & checkStructureAndGetMergeTreeData(IStorage & source_table, const StorageMetadataPtr & src_snapshot, const StorageMetadataPtr & my_snapshot) const;
    struct HardlinkedFiles