@Override
 public void setRecordHandler(
     @NotNull
         PersistentEnumeratorBase.RecordBufferHandler<PersistentEnumeratorBase> recordHandler) {
   myExternalKeysNoMapping = false;
   super.setRecordHandler(recordHandler);
 }
 @Override
 protected void doClose() throws IOException {
   try {
     super.doClose();
   } finally {
     btree.doClose();
   }
 }
 @Override
 protected void doFlush() throws IOException {
   btree.doFlush();
   storeVars(true);
   super.doFlush();
 }