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@Componentpublic 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 = 3500hystrix.threadpool.default.maxQueueSize = 60hystrix.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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