private List<String> verifySameColumnsForAllParts(
      List<String> colsToUpdateForAll, List<String> colsToUpdate) {
    if (colsToUpdateForAll == null) {
      return colsToUpdate;
    }
    if (colsToUpdate.size() != colsToUpdateForAll.size()) {
      return null;
    }
    // Assumes the lists are sorted.
    for (int i = 0; i < colsToUpdateForAll.size(); ++i) {
      if (!colsToUpdate.get(i).equals(colsToUpdateForAll.get(i))) {
        return null;
      }
    }
    return colsToUpdateForAll;
  }
Whether to only update stats that already exist and are out of date.
ql/src/java/org/apache/hadoop/hive/ql/stats/StatsUpdaterThread.java