@Override
 public SortedKeyValueIterator<Key, Value> deepCopy(final IteratorEnvironment env) {
   final NumericIndexStrategyFilterIterator iterator = new NumericIndexStrategyFilterIterator();
   iterator.indexStrategy = indexStrategy;
   iterator.rangeCache = rangeCache;
   iterator.source = source.deepCopy(env);
   return iterator;
 }
 @Override
 public synchronized SortedKeyValueIterator<K, V> deepCopy(IteratorEnvironment env) {
   return new SynchronizedIterator<K, V>(source.deepCopy(env));
 }