And waits for them. That's pointless.
mutation_kind == MutationsInterpreter::MutationKind::MUTATE_INDEX_PROJECTION ? Block{} : updated_header,
                new_data_part,
                in,
                time_of_mutation,
                compression_codec,
                merge_entry,
                need_remove_expired_values,
                need_sync,
                space_reservation,
                holder,
                context);
        }
        for (const auto & [rename_from, rename_to] : files_to_rename)
        {
            if (rename_to.empty() && new_data_part->checksums.files.count(rename_from))
            {
                new_data_part->checksums.files.erase(rename_from);
            }
            else if (new_data_part->checksums.files.count(rename_from))
            {
                new_data_part->checksums.files[rename_to] = new_data_part->checksums.files[rename_from];
                new_data_part->checksums.files.erase(rename_from);
            }
        }
        finalizeMutatedPart(source_part, new_data_part, need_remove_expired_values, compression_codec);
    }
    return new_data_part;
}
MergeAlgorithm MergeTreeDataMergerMutator::chooseMergeAlgorithm(