11 张图 | 讲透原理，最细的 Eureka 增量拉取

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大家好，我是悟空。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先说下哈，这篇文章画原理图用了很多时间。另外 Eureka 注册中心系列文章已经写到第六篇了，欢迎持续关注。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/95/958ad670b82e1701fcfc76b7e1e19d70.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"一、前言","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上一篇我们讲解了客户端首次获取注册表时，需要从注册中心全量拉取注册表到本地存着。那后续如果有客户端注册、下线的话，注册表肯定就发生变化了，这个时候客户端就得更新本地注册表了，怎么更新呢？下面我会带着大家一起来看下客户端第二次获取注册表的方式。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"题外话：之前写过一篇 Redis 主从同步的架构原理，里面也涉及到首次同步和第二次同步，其实原理也类似，但是 Redis 的主从同步原理要复杂些。强烈推荐配合着看一波：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzAwMjI0ODk0NA==&mid=2451958462&idx=1&sn=5380b7967443f88ef180ccd9db11fcc2&chksm=8d1c1321ba6b9a374ceeb993775d57800c4f98c3b5d4a85c3d3bc5eab649a2b0ca96c3db6c12#rd","title":"","type":null},"content":[{"type":"text","text":"镜 | 5 个维度深度剖析「主从架构」原理","attrs":{}}]}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"二、增量获取引发的问题","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面我们说到，当第一次获取全量信息后，本地就有注册信息了。那如果 Server 的注册表有更新，比如有服务注册、下线，Client 必须要重新获取一次注册表信息才行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那是否可以重新全量拉取一次呢？","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以是可以，但是，如果注册表信息很大呢？比如有几百个微服务都注册上去了，那一次拉取是非常耗时的，而且占用网络带宽，性能较差，这种方案是不靠谱的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以我们就需要用增量拉取注册信息表的方式，也就是说只拉取变化的数据，这样数据量就比较小了。如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/42/4239a3e5c11614088bc6d20af43da234.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"从源码里面我们可以看到，Eureka Client 通过调用 getAndUpdateDelta 方法获取增量的变化的注册表数据，Eureka Server 将变化的数据返回给 Client。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"这里就有几个问题","attrs":{}},{"type":"text","text":"：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（1）Client 隔多久进行一次增量获取？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（2）Server 将变化的数据存放在哪里？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（3）Client 如何将变化的数据合并到本地注册表里面？","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面分别针对上面的几个问题进行解答。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"三、间隔多久同步一次？","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.1 默认间隔时间","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"默认每隔 30 s 执行一次同步，如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/59/59e486aed70692982468f27304720f6c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这个 30 s 就是由变量 client.refresh.interval 定义的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Eureka 每 30 s 会调用一个后台线程去拉取增量注册表，这个后台线程的名字叫做：cacheRefresh。如下所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/e0/e0c1806dc93698b9d4907113e0381ab7.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.2 Client 发送拉取注册表的请求","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"就是调用 getDelta 方法，发送 HTTP请求调用 jersey 的 restful 接口，然后 Server 端的 Jersey 框架就会去处理这个请求了。发送请求的方法 getDelta 如下所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());\nrestful 接口的地址就长这样：\nhttp://localhost:8080/v2/apps/delta\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那么 Server 端如何过滤出增量的注册表信息呢？我们可以找到这个方法：getContainerDifferential。如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/94/9470abdccbb84b7d23be10c61bf40da9.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这个方法主要干的活就是去获取最近改变的数据。接下来我们看下最近改变的数据存放在哪。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"四、变化的数据存放在哪？","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.1 数据结构","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其实就是放在这个队列里面：recentlyChangedQueue。它的数据结构是一个并发安全的链表队列 ConcurrentLinkedQueue。链表里面存放的元素就是最近变化的注册信息 RecentlyChangedItem。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"ConcurrentLinkedQueue\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当有客户端注册的时候，这个链表里面的尾部就会追加一个对象。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"关于 ConcurrentLinkedQueue，还记得我之前写过的 18 种队列吗？不记得话看下这篇：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/nwY3t_Molqk-aOgwmVi9Uw","title":"","type":null},"content":[{"type":"text","text":"45张图庖丁解牛18种Queue，你知道几种？","attrs":{}}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ConcurrentLinkedQueue 是由链表结构组成的线程安全的先进先出无界队列。如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/85/85425d11f77fb427540d08a133ae3dfc.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.2 内部构造","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我觉得这个队列的构造还是非常值得我们学习的，我们来看下这个队列的构造，如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d0/d07783a4e21cadd61861220d6eed802f.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这个队列里面存放的对象是最近改变的对象 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"RecentlyChangedItem","attrs":{}}],"attrs":{}},{"type":"text","text":"。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"RecentlyChangedItem 存有三个元素：实例信息、操作类型和最后更新时间。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"实例信息","attrs":{}},{"type":"text","text":"：使用 Lease 保存一个客户端的注册表信息，这个在第四篇讲解注册表结构已经介绍过。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"操作类型","attrs":{}},{"type":"text","text":"：当有客户端发起注册、更新注册表、下线时，会设置 actionType，对应三种枚举值：新增、更新、删除。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"最后更新时间","attrs":{}},{"type":"text","text":"：客户端注册信息发生改变时，需要同时更新最后更新时间。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.3 最近的数据","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"既然上面说到是最近改变的数据才会放进去，那这个最近是多近呢？1 分钟？2分钟？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过源码我们找到了这个默认配置，","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"三分钟","attrs":{}}],"attrs":{}},{"type":"text","text":"刷新一次，也就是 180s 刷新一次。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/29/2980630ae0ac55f17f5eeac98b7efb82.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那刷新了什么？刷新其实是会遍历这个队列：recentlyChangedQueue。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"将队列里面的所有元素都遍历一遍，比对每个对象的最后更新时间是否超过了三分钟，如果超过了，就移除这个元素。如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ca/caa146890f033ff279afc201d34b5613.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当元素的最后更新时间超过 3 分钟未更新，则移除该元素。如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2e/2e70d5bab1118459e5690e458b106f3d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.4 检查间隔","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Server 端会将最近 3 分钟有更新的注册信息放入到队列中，超过 3 分钟未更新的数据将会被移除。那么多久会检查一次呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过源码我们找到，每隔 30s 就会调用一次检查任务。如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/67/675b4933337e8fcabb62863313c19310.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.5 小结","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Client 每隔 30 秒调用一次增量获取注册表的接口。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Server 每隔 30 秒调用检查一次队列。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果队列中有元素在 3 分钟以内都没有更新过，则从队列中移除该元素。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"五、客户端注册表合并","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这里有个问题：客户端首次拿到的全量注册表，存放本地了。第二次拿到的是增量的注册表，怎么将两次的数据合并在一起呢？如下图所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/87/8757a7f2c9a4b4b8fb2f07963237a333.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面我们来看看下客户端注册表合并的原理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当客户端调用获取增量注册表的请求后，注册表会返回增量信息，然后客户端就会调用本地合并的方法：updateDelta。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"合并注册表的原理图如下所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/89/891d547c6a47c6660c488bdcbb7886f0.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先就会遍历增量注册表，检查其中的每一项，不论 actionType 是新增、删除还是更新，如果本地本来就有，则执行后续的类型判断逻辑。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果实例信息的名字在","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"本地不存在","attrs":{}},{"type":"text","text":"则会先往本地注册表新增一个注册信息。然后本地肯定存在注册信息了，执行后续的判断逻辑。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当类型字段 actionType 等于新增或更新时，先删除后增加。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当类型字段 actionType 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合并操作，客户端终于完成了本地注册表的刷新，理论上来说，这个时候客户端的注册表应该和注册中心的注册表一致了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"但是如何确定是一致的呢？这里我们来考虑几种方案：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"再全量拉取一次注册表，和本地注册表进行比对。但是既然又要做一次全量拉取，那之前的增量拉取就没有必要了。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"拉取增量注册表，Server 返回全量注册表的实例 id，客户端比对每个实例 id 是否存在，以及检查本地是否有多余的，如果能匹配上，则认为是一致的。但是这里也有一个问题，对于新增和更新的注册实例，得把更新的实例信息的字段一一比对才能确定是否一致，这就太麻烦了。","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"另外还有一个致命的问题","attrs":{}},{"type":"text","text":"：如果客户端因为网络故障下线了，上一次最近 3 分钟的增量数据没有拉取到，那么相当于丢失了一次增量数据，这个时候，就不是完整的注册表信息了。","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有没有既方便又准确的比对方式呢？","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有的，那就是","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"哈希比对","attrs":{}}],"attrs":{}},{"type":"text","text":"。哈希比对的意思就是将两个对象经过哈希算法计算出两个 hash 值，如果两个 hash 值相等，则认为这两个对象相等。这种方式在代码中也非常常见，比如类的 hashcode() 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比对会不一致？答案在文中哦！","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下篇，注册中心的缓存架构走起！","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"作者简介","attrs":{}},{"type":"text","text":"：悟空，8年一线互联网开发和架构经验，用故事讲解分布式、架构设计、Java 核心技术。《JVM性能优化实战》专栏作者，开源了《Spring Cloud 实战 PassJava》项目，公众号：","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"悟空聊架构","attrs":{}}],"attrs":{}},{"type":"text","text":"。本文已收录至 ","attrs":{}},{"type":"link","attrs":{"href":"https://link.juejin.cn/?target=http%3A%2F%2Fwww.passjava.cn","title":"https://link.juejin.cn/?target=http%3A%2F%2Fwww.passjava.cn","type":null},"content":[{"type":"text","text":"www.passjava.cn","attrs":{}}]}]}]}