Hystrix隔离策略

Hystrix隔离方案

　　 Hystrix提供了两种隔离的解决方案：线程隔离和信号量隔离，默认为线程隔离。

private static final ExecutionIsolationStrategy default_executionIsolationStrategy = ExecutionIsolationStrategy.THREAD;

  public static enum ExecutionIsolationStrategy {
        THREAD, SEMAPHORE
    }

线程隔离

　　思路：请求被传入单独的线程池进行处理；
　　优点：存在超时机制；
　　缺点：线程切换和调度存在一定开销；

示例代码

package com.cainiao.test.test.hystrix;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;
import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixCommandProperties;
import com.netflix.hystrix.HystrixCommandProperties.ExecutionIsolationStrategy;
import com.netflix.hystrix.HystrixThreadPoolKey;
import com.netflix.hystrix.HystrixThreadPoolProperties;

public class CommandHelloWorld extends HystrixCommand<Void> {

    public CommandHelloWorld() {
        super(HystrixCommand.Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("g1"))
                .andCommandKey(HystrixCommandKey.Factory.asKey("k1"))
                // 设置线程池属性
                .andThreadPoolKey(HystrixThreadPoolKey.Factory.asKey("ThreadPool"))
                .andThreadPoolPropertiesDefaults(HystrixThreadPoolProperties.Setter().withCoreSize(5)
                        .withKeepAliveTimeMinutes(60).withMaxQueueSize(5).withQueueSizeRejectionThreshold(2))
                .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
                        // 开启熔断机制
                        .withCircuitBreakerEnabled(true)
                        // 熔断器开启3s后关闭
                        .withCircuitBreakerSleepWindowInMilliseconds(3000)
                        // 设置隔离策略
                        .withExecutionIsolationStrategy(ExecutionIsolationStrategy.THREAD)));
    }

    @Override
    protected Void run() {
        System.out.println("Hello world!");
        return null;
    }

}

信号量隔离

　　思路：请求被调用前，首先获取信号量，只有获得信号量的请求才会被处理；
　　优点：没有线程切换的开销；
　　缺点：没有超时机制；

package com.cainiao.test.test.hystrix;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;
import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixCommandProperties;
import com.netflix.hystrix.HystrixCommandProperties.ExecutionIsolationStrategy;

public class CommandHelloWorld extends HystrixCommand<Void> {

    public CommandHelloWorld() {
        super(HystrixCommand.Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("g1"))
                .andCommandKey(HystrixCommandKey.Factory.asKey("k1"))
                .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
                        // 开启熔断机制
                        .withCircuitBreakerEnabled(true)
                        // 熔断器开启3s后关闭
                        .withCircuitBreakerSleepWindowInMilliseconds(3000)
                        // 设置隔离策略
                        .withExecutionIsolationStrategy(ExecutionIsolationStrategy.SEMAPHORE)));
    }

    @Override
    protected Void run() {
        System.out.println("Hello world!");
        return null;
    }

}

The advantage of the thread pool approach is that requests that are passed to C can be timed out, something that is not possible when using semaphores.

参考：

1. https://stackoverflow.com/questions/30391809/what-is-bulkhead-pattern-used-by-hystrix；
2. https://github.com/Netflix/Hystrix/wiki/How-it-Works#Isolation；