presto-orc/src/main/java/io/prestosql/orc/reader/SliceDictionaryColumnReader.java/SliceDictionaryColumnReader/startRowGroup
class SliceDictionaryColumnReader:    @Override
    public void startRowGroup(InputStreamSources dataStreamSources)
    {
        presentStreamSource = dataStreamSources.getInputStreamSource(column, PRESENT, BooleanInputStream.class);
        dataStreamSource = dataStreamSources.getInputStreamSource(column, DATA, LongInputStream.class);

        readOffset = 0;
        nextBatchSize = 0;

        presentStream = null;
        dataStream = null;

        rowGroupOpen = false;
    }