MySQL“被動”性能優化彙總！

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"年少不知優化苦，遇坑方知優化難。 ——村口王大爺"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"本文內容導圖如下："}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/72/72b6843fc546b594f619612bbccb35d5.png","alt":"image.png","title":null,"style":null,"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}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我之前有很多文章都在講性能優化的問題，比如下面這些："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/icjByl5g3GvkgqLGIYakgQ","title":""},"content":[{"type":"text","text":"《switch 的性能提升了 3 倍，我只用了這一招！》"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/KQEWT-GAUqRvSv6sDVkUxw","title":""},"content":[{"type":"text","text":"《String性能提升10倍的幾個方法！(源碼+原理分析)》"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/O08zPGhgnWFEBIqh5oUmWw","title":""},"content":[{"type":"text","text":"《局部變量竟然比全局變量快 5 倍？》"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/ZraWOaOdYAJA7TV3Zx60Xw","title":""},"content":[{"type":"text","text":"《池化技術到達有多牛？看了線程和線程池的對比嚇我一跳！》"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/4O9MNTqS8eulExeY-RFKag","title":""},"content":[{"type":"text","text":"《鏈表竟然比數組慢了1000多倍？(動圖+性能評測)》"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/s/Zz6mofCtmYpABDL1ap04ow","title":""},"content":[{"type":"text","text":"《HashMap 的 7 種遍歷方式與性能分析！》"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":7,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://mp.weixin.qq.com/mp/appmsgalbum?_biz=MzU1NTkwODE4Mw==&action=getalbum&albumid=1337160373983690752&subscene=158&scenenote=https%3A%2F%2Fmp.weixin.qq.com%2Fs%3F__biz%3DMzU1NTkwODE4Mw%3D%3D%26mid%3D2247485176%26idx%3D1%26sn%3D961fcc0e4dd05a505ef0fc1eb5b10ac4%26chksm%3Dfbcc6bc0","title":""},"content":[{"type":"text","text":"更多性能優化文章"}]}]}]}]},{"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":"當然，本篇也是關於性能優化的，"},{"type":"text","marks":[{"type":"strong"}],"text":"那性能優化就應該一把梭子嗎？還是要符合一些規範和原則呢？"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/91/915bb95edff2e56f73605d0b6ba5d735.jpeg","alt":"代碼一把梭.jpg","title":null,"style":null,"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}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以，在開始之前（MySQL 優化），咱們先來聊聊性能優化的一些原則。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"性能優化原則和分類"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"性能優化一般可以分爲："}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"主動優化"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"被動優化"}]}]}]},{"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":"所謂的主動優化是指不需要外力的推動而自發進行的一種行爲，比如當服務沒有明顯的卡頓、宕機或者硬件指標異常的情況下，自我出發去優化的行爲，就可以稱之爲主動優化。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/af/af04953632db9918b9f161728e788c0a.gif","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"boxShadow"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"而被動優化剛好與主動優化相反，它是指在發現了服務器卡頓、服務異常或者物理指標異常的情況下，纔去優化的這種行爲。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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"}],"text":"性能優化原則"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"無論是主動優化還是被動優化都要符合以下性能優化的原則："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"優化不能改變服務運行的邏輯，要保證服務的"},{"type":"text","marks":[{"type":"strong"}],"text":"正確性"},{"type":"text","text":"；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"優化的過程和結果都要保證服務的"},{"type":"text","marks":[{"type":"strong"}],"text":"安全性"},{"type":"text","text":"；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"要保證服務的"},{"type":"text","marks":[{"type":"strong"}],"text":"穩定性"},{"type":"text","text":"，不能爲了追求性能犧牲程序的穩定性。比如不能爲了提高 Redis 的運行速度，而關閉持久化的功能，因爲這樣在 Redis 服務器重啓或者掉電之後會丟失存儲的數據。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/8d/8d4bccea52352ad2b9e69f8b1fd1ae5b.png","alt":"image.png","title":null,"style":null,"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":"以上原則看似都是些廢話，但卻給了我們一個啓發，那就是我們"},{"type":"text","marks":[{"type":"strong"}],"text":"性能優化手段應該是：預防性能問題爲主+被動優化爲輔"},{"type":"text","text":"。"}]},{"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":"也就是說，我們應該"},{"type":"text","marks":[{"type":"strong"}],"text":"以預防性能問題爲主"},{"type":"text","text":"，在開發階段儘可能的規避性能問題，而"},{"type":"text","marks":[{"type":"strong"}],"text":"在正常情況下，應儘量避免主動優化，以防止未知的風險"},{"type":"text","text":"（除非是爲了 KPI，或者是閒的沒事），尤其對生產環境而言更是如此，最後纔是考慮"},{"type":"text","marks":[{"type":"strong"}],"text":"被動優化"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"PS：當遇到性能緩慢下降、或硬件指標緩慢增加的情況，如今天內存的佔用率是 50%，明天是 70%，後天是 90% ，並且絲毫沒有收回的跡象時，我們應該提早發現並處理此類問題（這種情況也屬於被動優化的一種）。"}]}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"MySQL 被動性能優化"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以我們本文會"},{"type":"text","marks":[{"type":"strong"}],"text":"重點介紹 MySQL 被動性能優化的知識，根據被動性能優化的知識，你就可以得到預防性能問題發生的一些方法，從而規避 MySQL 的性能問題"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"本文我們會從問題入手，然後考慮這個問題產生的原因以及相應的優化方案。我們在實際開發中，通常會遇到以下 3 個問題："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"單條 SQL 運行慢；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"部分 SQL 運行慢；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"整個 SQL 運行慢。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/16/1692812895f5eaf97cb25e0e330d40d4.png","alt":"image.png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"問題 1：單條 SQL 運行慢"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"問題分析"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"造成單條 SQL 運行比較慢的常見原因有以下兩個："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"未正常創建或使用索引；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"表中數據量太大。"}]}]}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"解決方案 1：創建並正確使用索引"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"索引"},{"type":"text","text":"是一種能幫助 MySQL 提高查詢效率的主要手段，因此一般情況下我們遇到的單條 SQL 性能問題，通常都是由於未創建或爲正確使用索引而導致的，所以在遇到單條 SQL 運行比較慢的情況下，你"},{"type":"text","marks":[{"type":"strong"}],"text":"首先要做的就是檢查此表的索引是否正常創建"},{"type":"text","text":"。"}]},{"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":"如果表的索引已經創建了，"},{"type":"text","marks":[{"type":"strong"}],"text":"接下來就要檢查一下此 SQL 語句是否正常觸發了索引查詢"},{"type":"text","text":"，如果發生以下情況那麼 MySQL 將不能正常的使用索引："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"在 where 子句中使用 != 或者 <> 操作符，查詢引用會放棄索引而進行全表掃描；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"不能使用前導模糊查詢，也就是 '%XX' 或 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取模的方法，同時查詢、更新、刪除也是通過取模的方法來操作。"}]},{"type":"heading","attrs":{"align":null,"level":5},"content":[{"type":"text","text":"表的其他優化方案："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"使用可以存下數據最小的數據類型；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"使用簡單的數據類型，int 要比 varchar 類型在 MySQL 處理簡單；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"儘量使用 tinyint、smallint、mediumint 作爲整數類型而非 int；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"儘可能使用 not null 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SQL。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"解決方案：慢查詢分析"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MySQL 中自帶了慢查詢日誌的功能，開啓它就可以用來記錄在 MySQL 中響應時間超過閥值的語句，具體指運行時間超過 long"},{"type":"text","marks":[{"type":"italic"}],"text":"query"},{"type":"text","text":"time 值的 SQL，則會被記錄到慢查詢日誌中。long"},{"type":"text","marks":[{"type":"italic"}],"text":"query"},{"type":"text","text":"time 的默認值爲 10，意思是運行 10S 以上的語句。默認情況下，MySQL 數據庫並不啓動慢查詢日誌，需要我們手動來設置這個參數，如果不是調優需要的話，一般不建議啓動該參數，因爲開啓慢查詢日誌會給 MySQL 服務器帶來一定的性能影響。慢查詢日誌支持將日誌記錄寫入文件，也支持將日誌記錄寫入數據庫表。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用 "},{"type":"codeinline","content":[{"type":"text","text":"mysql> show variables like '%slow_query_log%';"}]},{"type":"text","text":" 來查詢慢查詢日誌是否開啓，執行效果如下圖所示："}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/17/17b2cba222c0b98186a7860a39d9a566.png","alt":"image.png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"slow"},{"type":"text","marks":[{"type":"italic"}],"text":"query"},{"type":"text","text":"log 的值爲 OFF 時，表示未開啓慢查詢日誌。"}]},{"type":"heading","attrs":{"align":null,"level":5},"content":[{"type":"text","text":"開啓慢查詢日誌"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"開啓慢查詢日誌，可以使用如下 MySQL 命令："}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"mysql> set global 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服務器了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"解決方案：讀寫分離"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"一般情況下對數據庫而言都是“讀多寫少”，換言之，數據庫的壓力多數是因爲大量的讀取數據的操作造成的，我們可以採用數據庫集羣的方案，使用一個庫作爲主庫，負責寫入數據；其他庫爲從庫，負責讀取數據。這樣可以緩解對數據庫的訪問壓力。"}]},{"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":"MySQL 常見的讀寫分離方案有以下兩種："}]},{"type":"heading","attrs":{"align":null,"level":5},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"1.應用層解決方案"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以通過應用層對數據源做路由來實現讀寫分離，比如，使用 SpringMVC + MyBatis，可以將 SQL 路由交給 Spring，通過 AOP 或者 Annotation 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服務器的穩定性，而被動優化常見的問題是："}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"單條 SQL 運行慢；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"部分 SQL 運行慢；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"整個 SQL 運行慢。"}]}]}]},{"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":"因此我們給出了每種被動優化方案的問題分析和解決方案，希望本文可以幫助到你。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}