presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/index/Indexer.java/Indexer/getIndexColumnFamily
class Indexer:    public static ByteBuffer getIndexColumnFamily(byte[] columnFamily, byte[] columnQualifier)
    {
        return wrap(ArrayUtils.addAll(ArrayUtils.add(columnFamily, UNDERSCORE), columnQualifier));
    }