private int getRgCount(StripeInformation stripe, int rowIndexStride) {
    return (int)Math.ceil((double)stripe.getNumberOfRows() / rowIndexStride);
  }
Determines which RGs need to be read, after stripes have been determined.
SARG is applied, and readState is populated for each stripe accordingly.
llap-server/src/java/org/apache/hadoop/hive/llap/io/encoded/OrcEncodedDataReader.java