private <T> T persistenceLoop(T sig, Class<T> clazz) throws IOException {
    RuntimeStatsPersister sp = RuntimeStatsPersister.INSTANCE;
    String stored = sp.encode(sig);
    return sp.decode(stored, clazz);
  }
This hook adds a persistence loop-back ensure that runtime statistics could be used.
ql/src/java/org/apache/hadoop/hive/ql/hooks/RuntimeStatsPersistenceCheckerHook.java