code: public static void gc() {
      class GCTask extends DTask<GCTask> {
        public GCTask() {super(GUI_PRIORITY);}
        @Override public void compute2() {
          Log.info("Calling System.gc() now...");
          System.gc();
          Log.info("System.gc() finished");
          tryComplete();
        }
      }
  
      for (H2ONode node : H2O.CLOUD._memary) {
        GCTask t = new GCTask();
        new RPC<>(node, t).call().get();
      }
    }
docs: Run System.gc() on every node in the H2O cluster.
  
  Having to call this manually from user code is a sign that something is wrong and a better
  heuristic is needed internally.