记一次Hystrix报错HystrixRuntimeException: HystrixCommandKey fallback execution rejected.

痛定思痛。 2022-12-22 11:27 457阅读 0赞

定位代码
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/com/netflix/hystrix/AbstractCommand.java:851

  1. if (fallbackSemaphore.tryAcquire()) { 
  2.                     try { 
  3.                         if (isFallbackUserDefined()) { 
  4.                             executionHook.onFallbackStart(this);
  5.                             fallbackExecutionChain = getFallbackObservable();
  6.                         } else { 
  7.                             //same logic as above without the hook invocation
  8.                             fallbackExecutionChain = getFallbackObservable();
  9.                         }
  10.                     } catch (Throwable ex) { 
  11.                         //If hook or user-fallback throws, then use that as the result of the fallback lookup
  12.                         fallbackExecutionChain = Observable.error(ex);
  13.                     }
  15.                     return fallbackExecutionChain
  16.                             .doOnEach(setRequestContext)
  17.                             .lift(new FallbackHookApplication(_cmd))
  18.                             .lift(new DeprecatedOnFallbackHookApplication(_cmd))
  19.                             .doOnNext(markFallbackEmit)
  20.                             .doOnCompleted(markFallbackCompleted)
  21.                             .onErrorResumeNext(handleFallbackError)
  22.                             .doOnTerminate(singleSemaphoreRelease)
  23.                             .doOnUnsubscribe(singleSemaphoreRelease);
  24.                 } else { 
  25.                    return handleFallbackRejectionByEmittingError();
  26.                 }

fallbackSemaphore.tryAcquire()
如果是信号量隔离那么走
com.netflix.hystrix.AbstractCommand.TryableSemaphoreActual

  1. @Override
  2.         public boolean tryAcquire() { 
  3.             int currentCount = count.incrementAndGet();
  4.             if (currentCount > numberOfPermits.get()) { 
  5.                 count.decrementAndGet();
  6.                 return false;
  7.             } else { 
  8.                 return true;
  9.             }
  10.         }

如果数量大于允许数量那么会返回false降级失败
也就是降级也有信号量的限制

数量初始化

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通过构造函数进行设置

  1. public TryableSemaphoreActual(HystrixProperty<Integer> numberOfPermits) { 
  2.             this.numberOfPermits = numberOfPermits;
  3.         }

fallbackSemaphorePerCircuit.putIfAbsent(commandKey.name(), new TryableSemaphoreActual(properties.fallbackIsolationSemaphoreMaxConcurrentRequests()));

数量是由HystrixCommandProperties的参数fallbackIsolationSemaphoreMaxConcurrentRequests决定

  1. protected TryableSemaphore getFallbackSemaphore() { 
  2.         if (fallbackSemaphoreOverride == null) { 
  3.             TryableSemaphore _s = fallbackSemaphorePerCircuit.get(commandKey.name());
  4.             if (_s == null) { 
  5.                 // we didn't find one cache so setup
  6.                 fallbackSemaphorePerCircuit.putIfAbsent(commandKey.name(), new TryableSemaphoreActual(properties.fallbackIsolationSemaphoreMaxConcurrentRequests()));
  7.                 // assign whatever got set (this or another thread)
  8.                 return fallbackSemaphorePerCircuit.get(commandKey.name());
  9.             } else { 
  10.                 return _s;
  11.             }
  12.         } else { 
  13.             return fallbackSemaphoreOverride;
  14.         }
  15.     }

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/com/netflix/hystrix/HystrixCommandProperties.java:128

  1. this.fallbackIsolationSemaphoreMaxConcurrentRequests = getProperty(propertyPrefix, key, "fallback.isolation.semaphore.maxConcurrentRequests", builder.getFallbackIsolationSemaphoreMaxConcurrentRequests(), default_fallbackIsolationSemaphoreMaxConcurrentRequests);

如果不设置失败信号量，那么失败信号量的数量为default_fallbackIsolationSemaphoreMaxConcurrentRequests

private static final Integer default_fallbackIsolationSemaphoreMaxConcurrentRequests = 10;

可以通过withFallbackIsolationSemaphoreMaxConcurrentRequests方法对参数进行设置

  1. HystrixCommandProperties
  2.                         .Setter()
  3.                         .withExecutionIsolationStrategy(HystrixCommandProperties.ExecutionIsolationStrategy.SEMAPHORE)
  4.                         .withExecutionIsolationSemaphoreMaxConcurrentRequests(1)
  5.                         .withFallbackIsolationSemaphoreMaxConcurrentRequests(100)

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