Redis-緩存雪崩，緩存擊穿，緩存穿透

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"一. 緩存雪崩"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"“雪崩來臨的時候沒有一片雪花是無辜的”。緩存雪崩就是大範圍甚至於整個redis提供的緩存服務不可用了，進而導致所有的請求都直接到了數據庫，甚至於擊垮整個服務鏈路。造成整個服務不可用。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"出現原因"},{"type":"text","text":"："}]},{"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":"給緩存設置了過期時間，且大範圍的緩存數據的過期時間一致。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"redis服務宕機。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"解決方案"},{"type":"text","text":"："}]},{"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":"提前預案: 給redis過期時間加隨機值預防大面積的緩存同時過期失效。redis集羣高可用可用，哨兵機制。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"兜底方案: 服務熔斷，服務降級。監控到緩存服務不可用時直接返回，或者限制流量直接請求到數據庫層。"}]}]}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"二. 緩存擊穿"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"相交於緩存雪崩大範圍或整體緩存不可用緩存擊穿則是指某個熱點key過期，導致的緩存失效。常常是一部分熱點數據，如秒殺產品的庫存數據。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"出現原因"},{"type":"text","text":"：熱點數據過期，或者被其他手段刪除。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"解決方案"},{"type":"text","text":"："}]},{"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":"對於熱點數據緩存時不設置過期時間。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"第一個請求發現熱點數據不在redis緩存中，可以先阻塞其他請求，等到第一個請求將數據庫數據讀出來並緩存到redis後再喚醒其他請求從緩存服務中讀取熱點數據。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"三. 緩存穿透"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"緩存穿透則是另外一個層面，指的時請求所訪問的數據既不在緩存中，也不在數據庫中。如果應用持續有大量請求訪問數據，就會同時給緩存和數據庫帶來巨大壓力。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"出現原因"},{"type":"text","text":"："}]},{"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":"業務層誤操作訪問到了不會存在的數據。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"惡意請求攻擊"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"解決方案"},{"type":"text","text":"："}]},{"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":"第一個請求發現熱點數據不在redis緩存中和數據庫中，可以先阻塞其他請求，緩存一個缺省值返回。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"利用redis提供的布隆過濾器。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"前端有效值校驗。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"四. 總結"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"緩存雪崩"},{"type":"text","text":" ，"},{"type":"text","marks":[{"type":"strong"}],"text":"緩存擊穿"},{"type":"text","text":" 均屬於緩存失效的一種異常緩存雪崩影響範圍大於緩存擊穿。"},{"type":"text","marks":[{"type":"strong"}],"text":"緩存穿透"},{"type":"text","text":" 則是數據本身就在整個數據存儲層。"}]},{"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}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}