presto-hive/src/main/java/io/prestosql/plugin/hive/SyncPartitionMetadataProcedure.java/SyncPartitionMetadataProcedure/difference
class SyncPartitionMetadataProcedure:    private static Set<String> difference(List<String> a, List<String> b)
    {
        return Sets.difference(new HashSet<>(a), new HashSet<>(b));
    }