CPU stuck between 95% to 100% for Standalone Jetty server

Question

I am using Jetty to start a main class as a service. Below a extract of the code to demonstrate the problem.

    Server server = new Server(8080);
    ResourceHandler resource_handler = new ResourceHandler();
    resource_handler.setDirectoriesListed(true);
    resource_handler.setWelcomeFiles(new String[] {"index.html"});
    resource_handler.setResourceBase(".");
    HandlerList handlers = new HandlerList();
    handlers.setHandlers(new Handler[] {resource_handler, new DefaultHandler()});
    server.setHandler(handlers);
    server.start();
    server.join();

I am running this application from eclipse on a windows machine with 2 CPU.

After I start this application, I execute below program on different machine. Below code just spawns 100 concurrent threads and executes a simple http request to get the index.html page.

ExecutorService service = Executors.newFixedThreadPool(100);
for (int i = 0; i < 10000; i++) {
  service.execute(new Runnable() {
    public void run() {
      try {
        long startTime = System.nanoTime();
        URL url = new URL("http://localhost:8080");
        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        conn.setRequestMethod("GET");
        long endTime = System.nanoTime();
        System.out.println(conn.getResponseMessage() + ":" + ((endTime - startTime)/1000000) + " (ms)");
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  });
}
service.shutdown();

When I execute this program, the server's CPU immediately reaches 100% (for both cores).

I have tried modifying maxThreads, acceptorThreads, buffer size parameters as suggested in https://wiki.eclipse.org/Jetty/Howto/High_Load.

But even then, the CPU still remains stuck between 95-100 for high load.

So the question here is, is there any configuration that I am missing to minimize the CPU? Or this is expected and can only be rectified by adding more CPUs or clustering the services?

Thanks for your help.

Joakim Erdfelt Joakim Erdfelt · Accepted Answer · 2015-01-06T13:16:38

You state you do run the ExecutorService part on a different machine, but the URL is http://localhost:8080. That's a no-no in load testing.

Some advice:

Don't have the Client Load and the Server Load on the same machine (don't cheat and attempt to put the load on 2 different VMs on a single physical machine)
Use multiple client machines, not just 1 (when the Jetty developers test load characteristics, we use at least 10:1 ratio of client machines to server machines)
Don't test with loopback, virtual network interfaces, localhost, etc.. Use a real network interface.
Don't test with unrealistic load scenarios. A real-world usage of your server will be a majority of HTTP/1.1 pipelined connections with multiple requests per physical connection. Some on fast networks, some on slow networks, some even on unreliable networks (think mobile)
If you must use HttpURLConnection, understand how it manages its HTTP version + connections (such as keep-alive or http/1.1 close), and make sure you read the response body content, close the streams, and disconnect() the connection.

Finally, be sure you are testing load in realistic ways.

CPU stuck between 95% to 100% for Standalone Jetty server

1 Answers