For some reasons when we delete a MergeTree Part in atomic way something may go wrong - and leave the `delete_tmp_*` folder or it's part on disk. This may lead to a disk space consumption over time.

It's suggested to delete this folders at least at server start-up. Current solution with `clearOldTemporaryDirectories()` doesn't work because this method is called periodically from a thread without any locks or advisory on folders - it may cause the race conditions.
{
    std::lock_guard background_processing_lock(currently_processing_in_background_mutex);
    return currently_merging_mutating_parts.contains(part);
}
std::shared_ptr<MergeMutateSelectedEntry> StorageMergeTree::selectPartsToMutate(
    const StorageMetadataPtr & metadata_snapshot, String * , TableLockHolder & ,
    std::unique_lock<std::mutex> & currently_processing_in_background_mutex_lock,
    bool & were_some_mutations_for_some_parts_skipped)
{
    size_t max_ast_elements = getContext()->getSettingsRef().max_expanded_ast_elements;
    auto future_part = std::make_shared<FutureMergedMutatedPart>();
    if (storage_settings.get()->assign_part_uuids)
        future_part->uuid = UUIDHelpers::generateV4();
    CurrentlyMergingPartsTaggerPtr tagger;
    if (current_mutations_by_version.empty())
        return {};
    size_t max_source_part_size = merger_mutator.getMaxSourcePartSizeForMutation();
    if (max_source_part_size == 0)
    {
        LOG_DEBUG(
            log,
            "Not enough idle threads to apply mutations at the moment. See settings 'number_of_free_entries_in_pool_to_execute_mutation' "
            "and 'background_pool_size'");
        return {};
    }