presto-orc/src/main/java/io/prestosql/orc/reader/SliceDirectColumnReader.java/SliceDirectColumnReader/openRowGroup
class SliceDirectColumnReader:    private void openRowGroup()
            throws IOException
    {
        presentStream = presentStreamSource.openStream();
        lengthStream = lengthStreamSource.openStream();
        dataStream = dataByteSource.openStream();

        rowGroupOpen = true;
    }