**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 :)

}
    else
    {
        is_custom_partitioned = true;
        checkPartitionKeyAndInitMinMax(metadata_.partition_key);
        min_format_version = MERGE_TREE_DATA_MIN_FORMAT_VERSION_WITH_CUSTOM_PARTITIONING;
    }
    setProperties(metadata_, metadata_, attach);
    
    merging_params.check(metadata_);
    if (metadata_.sampling_key.definition_ast != nullptr)
    {
        
        checkSampleExpression(metadata_, attach || settings->compatibility_allow_sampling_expression_not_in_primary_key,
                              settings->check_sample_column_is_correct && !attach);
    }
    checkTTLExpressions(metadata_, metadata_);
    
    PathWithDisk version_file;
    
    for (const auto & disk : getDisks())
    {
        if (disk->isBroken())
            continue;
        disk->createDirectories(relative_data_path);
        disk->createDirectories(fs::path(relative_data_path) / MergeTreeData::DETACHED_DIR_NAME);
        String current_version_file_path = fs::path(relative_data_path) / MergeTreeData::FORMAT_VERSION_FILE_NAME;
        if (disk->exists(current_version_file_path))
        {
            if (!version_file.first.empty())