public boolean isPermanentFunc(Class<?> udfClass) {
    // Note that permanent functions can only be properly checked from the session registry.
    // If permanent functions are read from the metastore during Hive initialization,
    // the JARs are not loaded for the UDFs during that time and so Hive is unable to instantiate
    // the UDf classes to add to the persistent functions set.
    // Once a permanent UDF has been referenced in a session its FunctionInfo should be registered
    // in the session registry (and persistent set updated), so it can be looked up there.
    return udfClass != null && persistent.containsKey(udfClass);
  }
@param udfClass Function class.
@return True iff the fnExpr represents a hive built-in function.
ql/src/java/org/apache/hadoop/hive/ql/exec/Registry.java