presto-orc/src/main/java/io/prestosql/orc/reader/TimestampColumnReader.java/TimestampColumnReader/openRowGroup
class TimestampColumnReader:    private void openRowGroup()
            throws IOException
    {
        presentStream = presentStreamSource.openStream();
        secondsStream = secondsStreamSource.openStream();
        nanosStream = nanosStreamSource.openStream();

        rowGroupOpen = true;
    }