Spring Cloud Hystrix线程池不足的解决方法

现象：

昨天突然线上很多接口获取失败，通过 kibana发现大量异常，具体异常信息：

...into fallback. Rejected command because thread-pool queueSize is at rejection threshold.

异常代码出处：

@FeignClient(name = "api", fallbackFactory = LoadBalancingFallbackFactory.class)
public interface LoadBalancingFeignClient {

  @PostMapping(value = "/api/loadBalancing/server")
  Result currentServer();

}

@Slf4j
@Component
public class LoadBalancingFallbackFactory implements FallbackFactory<LoadBalancingFeignClient> {

  @Override
  public LoadBalancingFeignClient create(Throwable throwable) {
    final String msg = throwable.getMessage();
    return () -> {
      log.error("loadBalancingFeignClient currentServer into fallback. {}", msg);
      return Result.error();
    };****
  }

}

原因：

看到这里已经很明显了，是由于hystrix线程池不够用，直接熔断导致的。
项目apollo配置：

hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds = 3500
hystrix.threadpool.default.maxQueueSize = 60
hystrix.threadpool.default.queueSizeRejectionThreshold = 40

hystrix参数简析：

maxQueueSize：线程池大小，默认为-1，创建的队列是SynchronousQueue，如果设置大于0则根据其大小创建LinkedBlockingQueue。

queueSizeRejectionThreshold：动态控制线程池队列的上限，即使maxQueueSize没有达到，达到queueSizeRejectionThreshold该值后，请求也会被拒绝，默认值5

相关源码：

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/strategy/concurrency/HystrixContextScheduler.java

  private class HystrixContextSchedulerWorker extends Worker {

    private final Worker worker;

    private HystrixContextSchedulerWorker(Worker actualWorker) {
      this.worker = actualWorker;
    }

    @Override
    public void unsubscribe() {
      worker.unsubscribe();
    }

    @Override
    public boolean isUnsubscribed() {
      return worker.isUnsubscribed();
    }

    @Override
    public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
      if (threadPool != null) {
        if (!threadPool.isQueueSpaceAvailable()) {
          throw new RejectedExecutionException("Rejected command because thread-pool queueSize is at rejection threshold.");
        }
      }
      return worker.schedule(new HystrixContexSchedulerAction(concurrencyStrategy, action), delayTime, unit);
    }

    @Override
    public Subscription schedule(Action0 action) {
      if (threadPool != null) {
        if (!threadPool.isQueueSpaceAvailable()) {
          throw new RejectedExecutionException("Rejected command because thread-pool queueSize is at rejection threshold.");
        }
      }
      return worker.schedule(new HystrixContexSchedulerAction(concurrencyStrategy, action));
    }

  }

解决办法：

• 适当调大Hystrix线程队列参数
• 动态水平扩容服务
• 优化下游服务，减少服务响应时间

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