ExecutorService slow and hung sometime

I am calling the multiple rest API and for this i am using the ExecutorService for parallel processing. Consumer hit my app more than 10 times every seconds and i observed ExecutorService very slow to response. I have deployed my application on kubernetes using tomcat web server.
below is my code , not sure what is causing this to slow.

   ExecutorService WORKER_THREAD_POOL = Executors.newFixedThreadPool(100);

            Collection tasks = new ArrayList();
  for( String str: datalist){
 tasks.add(new MyThreadPool(str)); // MyThreadPool internally calls the REST API using Google HttpRequest.
}
 List<Future<BasePolicy>> futures = null;
            try {
                long startProcessingTime = System.currentTimeMillis();
                futures = WORKER_THREAD_POOL.invokeAll(tasks);
                WORKER_THREAD_POOL.shutdown();

                if (!WORKER_THREAD_POOL.awaitTermination(60000, TimeUnit.SECONDS)) {
                    WORKER_THREAD_POOL.shutdownNow();
                }

                long totalProcessingTime = System.currentTimeMillis() - startProcessingTime;
                log.info("total time to complete the thread pool- " + totalProcessingTime);
            } catch (InterruptedException e) {
                log.error("error occured during ASYNC process ");
                e.printStackTrace();
            }
            log.info("Finished Waiting All threads completed ");
            for (Future<Data> mFuture : futures) {
               // my logic 
            }

</details>


# 答案1
**得分**: 2

ExecutorService非常慢响应。 <br>

ExecutorService WORKER_THREAD_POOL = Executors.newFixedThreadPool(100);

让我们从这个问题开始：您的机器有多少个核心？ <br>
对于`newFixedThreadPool`，建议开始使用与您的机器核心数相同数量的线程（如果任务需要较长时间）。使用值为`100`时，您的CPU将忙于**调度和上下文切换**。此外，由于它是一个`newFixedThreadPool`，即使负载较轻，许多线程也会保留在池中，对CPU毫无帮助。

如《Effective Java》所建议，`newCachedThreadPool`通常做得不错。
[这里][1]有更多关于线程池的信息。

如果您期望有重负载，我认为在多台服务器上部署应用程序是明智的选择（这取决于您的单台服务器的容量）。线程不会有帮助，最终可能会导致应用程序变慢。

  [1]: https://stackoverflow.com/questions/17957382/fixedthreadpool-vs-cachedthreadpool-the-lesser-of-two-evils

<details>
<summary>英文:</summary>

&gt; and i observed ExecutorService very slow to response. &lt;br&gt;

    ExecutorService WORKER_THREAD_POOL = Executors.newFixedThreadPool(100);

Let&#39;s start with the question: How many cores does your machine have? &lt;br&gt;
For, `newFixedThreadPool`, it is suggested to start with as many threads as the number of cores in your machine (if the tasks are long running ones). With a value of `100`, your CPU is going to be busy with **scheduling and context-switching**. On top of that, since it&#39;s a `newFixedThreadPool`, so many threads are going to remain in pool even when there is less load - not helpin the CPU.

As suggested in *Effective Java*, `newCachedThreadPool` *usually does the good thing*. 
[Here][1] is more on the Thread Pools.

If you are expecting a really heavy load, I think deployment of apps on multiple servers would be the wise thing to do (this depends on the capacity of your single server). Threads are not going to help and can eventually make your app slow.


  [1]: https://stackoverflow.com/questions/17957382/fixedthreadpool-vs-cachedthreadpool-the-lesser-of-two-evils

</details>



# 答案2
**得分**: 0

当您在Kubernetes中部署应用程序时，如果不指定`memory`和`cpu`的要求，Kubernetes调度程序将以尽力而为的方式将Pod调度到节点上，这可能导致饥饿甚至Pod被驱逐。

您可以通过以下方式帮助调度程序做出更好的调度决策，指定`memory`和`cpu`的要求：

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: frontend
spec:
  containers:
  - name: app
    image: images.my-company.example/app:v4
    env:
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"

这将确保Pod被调度到能够满足起始要求的节点上，即64Mi内存和250m CPU，并允许它在需要时扩展到128Mi内存和500m CPU。

apiVersion: v1
kind: Pod
metadata:
  name: frontend
spec:
  containers:
  - name: app
    image: images.my-company.example/app:v4
    env:
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"