I am reading clickhouse mutation code. In StorageMergeTree->selectPartsToMutate() function, there is a check 
`if (current_ast_elements + commands_size >= max_ast_elements)
                break;`

I think if there are many mutations then the check result will be true, so that it will skip the remaining mutations.
But the new part's mutation is set to the last one in mutation map, and it does not apply the remaining mutations actually.
`new_part_info.mutation = current_mutations_by_version.rbegin()->first;`

Then the new part will miss the remaining mutations in future mutation job.

I think it's wrong here. Am I right?

If it is right, I will submit a PR 

auto lower = std::lower_bound(block_numbers_on_disk.begin(), block_numbers_on_disk.end(), std::make_pair(min_block, Int64(-1L)));
        if (lower != block_numbers_on_disk.end() && min_block >= lower->first && max_block <= lower->second)
            return true;
        if (lower != block_numbers_on_disk.begin())
        {
            --lower;
            if (min_block >= lower->first && max_block <= lower->second)
                return true;
        }
        return false;
    };
    size_t cleared_count = 0;
    auto disks = getStoragePolicy()->getDisks();
    for (auto disk_it = disks.rbegin(); disk_it != disks.rend(); ++disk_it)
    {
        auto disk_ptr = *disk_it;
        for (auto it = disk_ptr->iterateDirectory(relative_data_path); it->isValid(); it->next())
        {
            auto min_max_block_number = MergeTreeWriteAheadLog::tryParseMinMaxBlockNumber(it->name());
            if (min_max_block_number && is_range_on_disk(min_max_block_number->first, min_max_block_number->second))
            {
                LOG_DEBUG(log, "Removing from filesystem the outdated WAL file " + it->name());
                disk_ptr->removeFile(relative_data_path + it->name());
                ++cleared_count;
            }
        }
    }
    return cleared_count;
}
size_t MergeTreeData::clearEmptyParts()