private Object getOldKey(RegionEntry entry) throws TypeMismatchException {
    Object oldKey = null;
    if (IndexManager.isObjectModificationInplace() && entryToValuesMap.containsKey(entry)) {
      oldKey = entryToValuesMap.get(entry);
    } else if (!IndexManager.isObjectModificationInplace() && entryToOldKeysMap != null) {
      Map oldKeyMap = entryToOldKeysMap.get();
      if (oldKeyMap != null) {
        oldKey = TypeUtils.indexKeyFor(oldKeyMap.get(entry));
      }
    }
    return oldKey;
  }
Add/Updates the index forward and reverse map. If index key for a RegionEntry is found same as
previous key no update is performed.

This also updates the {@link IndexStatistics} numKeys and numValues as and when appropriate.
One thing to notice though is no increment in numValues is performed if old key and new index
key are found equal using {@link Object#equals(Object)}.
geode-core/src/main/java/org/apache/geode/cache/query/internal/index/HashIndex.java