presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorSplitManager.java/RaptorSplitManager/selectRandom
class RaptorSplitManager:    private static <T> T selectRandom(Iterable<T> elements)
    {
        List<T> list = ImmutableList.copyOf(elements);
        return list.get(ThreadLocalRandom.current().nextInt(list.size()));
    }