@Override
  public CloseableIterator<IndexStoreEntry> descendingIterator(Collection keysToRemove) {
    return new MapIndexStoreIterator(indexMap.descendingIterator(), keysToRemove, indexOnValues,
        indexOnRegionKeys);
  }
Implementation of IndexStorage that is backed by an IndexMap
geode-core/src/main/java/org/apache/geode/cache/query/internal/index/MapIndexStore.java