11 張圖 | 講透原理，最細的 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":"先說下哈，這篇文章畫原理圖用了很多時間。另外 Eureka 註冊中心繫列文章已經寫到第六篇了，歡迎持續關注。","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":"上一篇我們講解了客戶端首次獲取註冊表時，需要從註冊中心全量拉取註冊表到本地存着。那後續如果有客戶端註冊、下線的話，註冊表肯定就發生變化了，這個時候客戶端就得更新本地註冊表了，怎麼更新呢？下面我會帶着大家一起來看下客戶端第二次獲取註冊表的方式。","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":"題外話：之前寫過一篇 Redis 主從同步的架構原理，裏面也涉及到首次同步和第二次同步，其實原理也類似，但是 Redis 的主從同步原理要複雜些。強烈推薦配合着看一波：","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":"鏡 | 5 個維度深度剖析「主從架構」原理","attrs":{}}]}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"二、增量獲取引發的問題","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面我們說到，當第一次獲取全量信息後，本地就有註冊信息了。那如果 Server 的註冊表有更新，比如有服務註冊、下線，Client 必須要重新獲取一次註冊表信息纔行。","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，如果註冊表信息很大呢？比如有幾百個微服務都註冊上去了，那一次拉取是非常耗時的，而且佔用網絡帶寬，性能較差，這種方案是不靠譜的。","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":"所以我們就需要用增量拉取註冊信息表的方式，也就是說只拉取變化的數據，這樣數據量就比較小了。如下圖所示：","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":"從源碼裏面我們可以看到，Eureka Client 通過調用 getAndUpdateDelta 方法獲取增量的變化的註冊表數據，Eureka Server 將變化的數據返回給 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":"這裏就有幾個問題","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 隔多久進行一次增量獲取？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（2）Server 將變化的數據存放在哪裏？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（3）Client 如何將變化的數據合併到本地註冊表裏面？","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":"下面分別針對上面的幾個問題進行解答。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"三、間隔多久同步一次？","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.1 默認間隔時間","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"默認每隔 30 s 執行一次同步，如下圖所示：","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":"這個 30 s 就是由變量 client.refresh.interval 定義的。","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 會調用一個後臺線程去拉取增量註冊表，這個後臺線程的名字叫做：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 發送拉取註冊表的請求","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"就是調用 getDelta 方法，發送 HTTP請求調用 jersey 的 restful 接口，然後 Server 端的 Jersey 框架就會去處理這個請求了。發送請求的方法 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 接口的地址就長這樣：\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":"那麼 Server 端如何過濾出增量的註冊表信息呢？我們可以找到這個方法：getContainerDifferential。如下圖所示：","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":"這個方法主要乾的活就是去獲取最近改變的數據。接下來我們看下最近改變的數據存放在哪。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"四、變化的數據存放在哪？","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.1 數據結構","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其實就是放在這個隊列裏面：recentlyChangedQueue。它的數據結構是一個併發安全的鏈表隊列 ConcurrentLinkedQueue。鏈表裏面存放的元素就是最近變化的註冊信息 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":"當有客戶端註冊的時候，這個鏈表裏面的尾部就會追加一個對象。","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":"關於 ConcurrentLinkedQueue，還記得我之前寫過的 18 種隊列嗎？不記得話看下這篇：","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張圖庖丁解牛18種Queue，你知道幾種？","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 是由鏈表結構組成的線程安全的先進先出無界隊列。如下圖所示：","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 內部構造","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我覺得這個隊列的構造還是非常值得我們學習的，我們來看下這個隊列的構造，如下圖所示：","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":"這個隊列裏面存放的對象是最近改變的對象 ","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 存有三個元素：實例信息、操作類型和最後更新時間。","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":"實例信息","attrs":{}},{"type":"text","text":"：使用 Lease 保存一個客戶端的註冊表信息，這個在第四篇講解註冊表結構已經介紹過。","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":"操作類型","attrs":{}},{"type":"text","text":"：當有客戶端發起註冊、更新註冊表、下線時，會設置 actionType，對應三種枚舉值：新增、更新、刪除。","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":"最後更新時間","attrs":{}},{"type":"text","text":"：客戶端註冊信息發生改變時，需要同時更新最後更新時間。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4.3 最近的數據","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"既然上面說到是最近改變的數據纔會放進去，那這個最近是多近呢？1 分鐘？2分鐘？","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":"通過源碼我們找到了這個默認配置，","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"三分鐘","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":"那刷新了什麼？刷新其實是會遍歷這個隊列：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":"將隊列裏面的所有元素都遍歷一遍，比對每個對象的最後更新時間是否超過了三分鐘，如果超過了，就移除這個元素。如下圖所示：","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":"當元素的最後更新時間超過 3 分鐘未更新，則移除該元素。如下圖所示：","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 檢查間隔","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Server 端會將最近 3 分鐘有更新的註冊信息放入到隊列中，超過 3 分鐘未更新的數據將會被移除。那麼多久會檢查一次呢？","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":"通過源碼我們找到，每隔 30s 就會調用一次檢查任務。如下圖所示：","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 小結","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 秒調用一次增量獲取註冊表的接口。","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 秒調用檢查一次隊列。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果隊列中有元素在 3 分鐘以內都沒有更新過，則從隊列中移除該元素。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"五、客戶端註冊表合併","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這裏有個問題：客戶端首次拿到的全量註冊表，存放本地了。第二次拿到的是增量的註冊表，怎麼將兩次的數據合併在一起呢？如下圖所示：","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":"下面我們來看看下客戶端註冊表合併的原理。","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":"當客戶端調用獲取增量註冊表的請求後，註冊表會返回增量信息，然後客戶端就會調用本地合併的方法：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":"合併註冊表的原理圖如下所示：","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":"首先就會遍歷增量註冊表，檢查其中的每一項，不論 actionType 是新增、刪除還是更新，如果本地本來就有，則執行後續的類型判斷邏輯。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果實例信息的名字在","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"本地不存在","attrs":{}},{"type":"text","text":"則會先往本地註冊表新增一個註冊信息。然後本地肯定存在註冊信息了，執行後續的判斷邏輯。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當類型字段 actionType 等於新增或更新時，先刪除後增加。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當類型字段 actionType 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是否存在，以及檢查本地是否有多餘的，如果能匹配上，則認爲是一致的。但是這裏也有一個問題，對於新增和更新的註冊實例，得把更新的實例信息的字段一一比對才能確定是否一致，這就太麻煩了。","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"另外還有一個致命的問題","attrs":{}},{"type":"text","text":"：如果客戶端因爲網絡故障下線了，上一次最近 3 分鐘的增量數據沒有拉取到，那麼相當於丟失了一次增量數據，這個時候，就不是完整的註冊表信息了。","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":"有沒有既方便又準確的比對方式呢？","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":"哈希比對","attrs":{}}],"attrs":{}},{"type":"text","text":"。哈希比對的意思就是將兩個對象經過哈希算法計算出兩個 hash 值，如果兩個 hash 值相等，則認爲這兩個對象相等。這種方式在代碼中也非常常見，比如類的 hashcode() 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比對會不一致？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，註冊中心的緩存架構走起！","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":"作者簡介","attrs":{}},{"type":"text","text":"：悟空，8年一線互聯網開發和架構經驗，用故事講解分佈式、架構設計、Java 核心技術。《JVM性能優化實戰》專欄作者，開源了《Spring Cloud 實戰 PassJava》項目，公衆號：","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"悟空聊架構","attrs":{}}],"attrs":{}},{"type":"text","text":"。本文已收錄至 ","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":{}}]}]}]}