dubbo3一致性负载均衡，请示服务提供者会变化，负载均衡没有生效

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已于 2022-02-02 17:46:04 修改

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#负载均衡 #dubbo

于 2022-02-02 17:45:28 首次发布

本文分析了Dubbo 3.0.5中ConsistentHashLoadBalance的实现变化，指出与2.7.10版本的不一致行为，并探讨可能的原因和场景影响。通过源码解读，揭示了请求分发策略的调整及其对一致性原则的影响。

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问题描述

dubbo版本3.0.5，两个服务提供者A、B

当消费者请示OrderService 服务时，A调用三次，然后B调用一次，然后A调用三次，然后B调用一次，不断循环，相同请示没有有只请示一个服务者。

java源代码

    @DubboReference(version="b",loadbalance = "consistenthash")
    public OrderService orderServiceB;

dubbo3.0.5的ConsistentHashLoadBalance.java 源代码

        private Invoker<T> selectForKey(long hash) {
            Map.Entry<Long, Invoker<T>> entry = virtualInvokers.ceilingEntry(hash);
            if (entry == null) {
                entry = virtualInvokers.firstEntry();
            }

            String serverAddress = entry.getValue().getUrl().getAddress();

            /**
             * The following part of codes aims to select suitable invoker.
             * This part is not complete thread safety.
             * However, in the scene of consumer-side load balance,
             * thread race for this part of codes
             * (execution time cost for this part of codes without any IO or
             * network operation is very low) will rarely occur. And even in
             * extreme case, a few requests are assigned to an invoker which
             * is above OVERLOAD_RATIO_THREAD will not make a significant impact
             * on the effect of this new algorithm.
             * And make this part of codes synchronized will reduce ef

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