@Override
    public int compare(VersionTag o1, VersionTag o2) {
      long result = o1.getRegionVersion() - o2.getRegionVersion();
      if (result == 0) {
        result = o1.getVersionTimeStamp() - o2.getVersionTimeStamp();
      }
      return Long.signum(result);
    }
A comparator that sorts version tags based on the region version, and then on the timestamp.
geode-core/src/main/java/org/apache/geode/internal/cache/OrderedTombstoneMap.java