presto-orc/src/main/java/io/prestosql/orc/writer/SliceDirectColumnWriter.java/SliceDirectColumnWriter/beginRowGroup
class SliceDirectColumnWriter:    @Override
    public void beginRowGroup()
    {
        checkState(!closed);
        presentStream.recordCheckpoint();
        lengthStream.recordCheckpoint();
        dataStream.recordCheckpoint();
    }