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

        readOffset = 0;
        nextBatchSize = 0;

        presentStream = null;
        secondsStream = null;
        nanosStream = null;

        rowGroupOpen = false;
    }