When executing clhsdb commands that walk the heap, such as scanoops or dumpheap, you will see the following in the output just once (and only the first time the command is executed):

InstanceStackChunkKlass: InstanceStackChunkKlass

It comes from InstanceStackChunkKlass.initialize():

  private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
    // Just make sure it's there for now
    Type type = db.lookupType("InstanceStackChunkKlass");
    java.lang.Thread.currentThread().dumpStack();
    System.out.println("InstanceStackChunkKlass: " + type);
  }

It's purpose was really just a reminder that SA still does not scan virtual thread StackChunks. We have JDK-8261848 to cover that. Note the presence of the output happens even if virtual threads are not used, so it should be removed.