{"id":40286,"date":"2024-11-26T14:00:29","date_gmt":"2024-11-26T06:00:29","guid":{"rendered":"https:\/\/fwq.ai\/blog\/40286\/"},"modified":"2024-11-26T14:00:29","modified_gmt":"2024-11-26T06:00:29","slug":"linux%e5%86%85%e6%a0%b8%e4%b8%ad%e7%9a%84hash%e4%b8%8ebucket%e7%ae%80%e5%8d%95%e4%bb%8b%e7%bb%8d","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/40286\/","title":{"rendered":"Linux\u5185\u6838\u4e2d\u7684hash\u4e0ebucket\u7b80\u5355\u4ecb\u7ecd"},"content":{"rendered":"

 <\/p>\n

\"Linux\u5185\u6838\u4e2d\u7684hash\u4e0ebucket\u7b80\u5355\u4ecb\u7ecd\u63d2\u56fe\"<\/p>\n

\u54c8\u5e0c\u51fd\u6570(Hash Function)\u4e3a\u6839\u636e\u7d22\u5f15\u952e\u6765\u8fd4\u56de\u6570\u503c\u54c8\u5e0c\u7a0b\u5e8f\u4ee3\u7801\u7684\u7b97\u6cd5\u3002\u7d22\u5f15\u952e(Key)\u662f\u88ab\u5b58\u50a8\u5bf9\u8c61\u7684\u67d0\u4e9b\u5c5e\u6027\u503c(Value)\u3002\u5f53\u5bf9\u8c61\u52a0\u5165\u81f3 Hashtable\u65f6\uff0c\u5b83\u5b58\u50a8\u5728\u4e0e\u5bf9\u8c61\u54c8\u5e0c\u7a0b\u5e8f\u4ee3\u7801\u76f8\u7b26\u7684\u54c8\u5e0c\u7a0b\u5e8f\u4ee3\u7801\u76f8\u5173\u7684Bucket\u4e2d\u3002\u5f53\u5728Hashtable\u5185\u641c\u5bfb\u503c\u65f6\uff0c\u54c8\u5e0c\u7a0b\u5e8f\u4ee3\u7801\u4f1a\u4e3a\u8be5\u503c\u4ea7\u751f\uff0c\u5e76\u4e14\u4f1a\u641c\u5bfb\u4e0e\u8be5\u54c8\u5e0c\u7a0b\u5e8f\u4ee3\u7801\u76f8\u5173\u7684Bucket\u3002\u4f8b\u5982\uff0cstudent\u548cteacher\u4f1a\u653e\u5728\u4e0d\u540c\u7684Bucket\u4e2d\uff0c\u800cdog\u548cgod\u4f1a\u653e\u5728\u76f8\u540c\u7684 Bucket\u4e2d\u3002\u6240\u4ee5\u5f53\u7d22\u5f15\u952e\u662f\u552f\u4e00\u4eceHashtable\u83b7\u53d6\u5143\u7d20\u7684\u6027\u80fd\u65f6\u8868\u73b0\u4f1a\u8f83\u597d\u3002Hash\u7684\u56db\u5927\u4f18\u70b9\u5982\u4e0b\u6240\u793a\u3002<\/p>\n

\u00b7 \u4e8b\u5148\u4e0d\u9700\u8981\u6392\u5e8f\u3002<\/p>\n

\u00b7 \u641c\u5bfb\u901f\u5ea6\u4e0e\u6570\u636e\u591a\u5c11\u65e0\u5173\u3002<\/p>\n

\u00b7 \u6570\u5b57\u7b7e\u540d\u7684\u5bc6\u7801\u6280\u672f\u4fdd\u5bc6\u6027(Security)\u9ad8\u3002<\/p>\n

\u00b7 \u53ef\u505a\u6570\u636e\u538b\u7f29(Data Compression)\uff0c\u4ee5\u8282\u7701\u7a7a\u95f4\u3002<\/p>\n

Linux\u5185\u6838\u91cc\u7684\u54c8\u5e0c\u8868\u5e94\u7528\u975e\u5e38\u5e7f\u6cdb\uff0cPHP\u5185\u6838\u91cc\u5927\u90e8\u5206\u8bed\u8a00\u7279\u6027\u4e5f\u662f\u57fa\u4e8e\u54c8\u5e0c\u8868\u5b9e\u73b0\u7684\u3002\u4e3a\u4ec0\u4e48\u54c8\u5e0c\u8868\u80fd\u8fd9\u4e48\u795e\u901a\u5e7f\u5927?\u54c8\u5e0c\u8868\u80fd\u591f\u5b9e\u73b0\u9ad8\u6548\u7684\u6570\u636e\u5b58\u50a8\u548c\u67e5\u627e\uff0c\u800c\u5b58\u50a8\u548c\u67e5\u627e\u662f\u7f16\u7a0b\u4e2d\u5e94\u7528\u6700\u5e7f\u6cdb\u7684\u4e24\u4e2a\u64cd\u4f5c\u3002<\/p>\n

Linux\u5185\u6838\u91cc\u7684\u54c8\u5e0c\u8868<\/strong> <\/p>\n

\u8bfb\u8fc7Linux\u5185\u6838\u6e90\u7801\u7684\u4eba\u53ef\u80fd\u90fd\u4f1a\u53d1\u73b0\uff0c\u5176\u4e2d\u5e76\u6ca1\u6709\u592a\u591a\u590d\u6742\u7684\u6570\u636e\u7ed3\u6784\uff0c\u4f5c\u4e3a\u57fa\u7840\u6570\u636e\u7ed3\u6784\u7684\u53cc\u5411\u94fe\u8868(list)\u548c\u57fa\u4e8elist\u5b9e\u73b0\u7684hash\u8868\u5360\u636e\u4e86\u7edd\u5927\u90e8\u5206\u6570\u636e\u7ed3\u6784\u3002\u5185\u6838\u4e3a\u4ec0\u4e48\u4f1a\u5927\u91cf\u4f7f\u7528\u8fd9\u4e24\u79cd\u6570\u636e\u7ed3\u6784\u5462?
\u9996\u5148\uff0c\u8fd9\u4e24\u79cd\u6570\u636e\u7ed3\u6784\u90fd\u5341\u5206\u7b80\u5355\uff0c\u7b80\u5355\u5305\u62ec\u7406\u89e3\u8d77\u6765\u7b80\u5355\u548c\u4f7f\u7528\u8d77\u6765\u7b80\u5355\u4e24\u65b9\u9762\u5185\u5bb9\u3002\u8fd9\u4e5f\u610f\u5473\u7740\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u548c\u53ef\u7ef4\u62a4\u6027\u90fd\u6bd4\u5176\u4ed6\u590d\u6742\u7684\u6570\u636e\u7ed3\u6784\u8981\u597d\uff0c\u51fa\u73b0bug\u7684\u98ce\u9669\u4e5f\u8f83\u4f4e\u3002\u4ece\u54f2\u5b66\u4e0a\u6765\u8bb2\uff0c\u8fd9\u4e5f\u7b26\u5408K.I.S.S.\u6761\u6b3e\u3002<\/p>\n

\u5176\u6b21\uff0c\u5185\u6838\u662f\u4e00\u4e2a\u6bd4\u8f83\u8bb2\u7a76\u6027\u80fd\u7684\u8f6f\u4ef6\uff0c\u4e3a\u4e86\u7a0b\u5e8f\u8bbe\u8ba1\u548c\u7ef4\u62a4\u7684\u7b80\u5355\u6027\u800c\u5931\u6389\u6027\u80fd\uff0c\u8fd9\u7a76\u7adf\u662f\u4e0d\u662f\u7b97\u5f97\u4e0d\u507f\u5931\u5462?\u6211\u4eec\u662f\u4e0d\u662f\u5e94\u8be5\u5c06\u5929\u5e73\u66f4\u52a0\u504f\u5411\u4e8e\u6027\u80fd?\u5df2\u7ecf\u8bb0\u4e0d\u8d77\u662f\u5728\u54ea\u91cc\u542c\u8bf4\u8fc7\uff0c\u5f88\u591a\u5546\u4e1a\u7684\u8def\u7531\u8f6f\u4ef6\u90fd\u662f\u57fa\u4e8e\u4e8c\u53c9\u6811\u7684\u6570\u636e\u7ed3\u6784\u6765\u5b58\u50a8\u8def\u7531\u9879\uff0c\u4ee5\u6c42\u5f97\u5176\u8def\u7531\u67e5\u627e\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u4e3alog(n)\uff0c\u5e76\u4e14\u4ed6\u6279\u8bc4Linux\u7684\u8def\u7531\u9879\u7ec4\u7ec7\u4e3ahash\u8868\uff0c\u81f4\u4f7f\u6027\u80fd\u4e0d\u4f73\uff0c\u4e0d\u9002\u5408\u5546\u4e1a\u3002\u786e\u5b9e\u6709\u4e00\u5b9a\u9053\u7406\uff0c\u53ef\u4ed4\u7ec6\u5206\u6790\uff0chash\u8868\u7684\u6027\u80fd\u771f\u7684\u6bd4\u4e8c\u53c9\u6811\u5dee\u4e48?\u4e8c\u53c9\u6811\u7684\u63d2\u5165\u548c\u5220\u9664\u67d0\u4e00\u9879\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u90fd\u4e3alog(n);hash\u8868\u63d2\u5165\u548c\u5220\u9664\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u6700\u597d\u4e3aO(1)\uff0c\u6700\u5dee\u4e3aO(n)\uff0c\u5982\u679c\u9009\u53d6\u7684\u8868\u9879(m)\u8db3\u591f\u591a\uff0c\u4e14hash\u51fd\u6570\u8db3\u591f\u597d\u7684\u8bdd\uff0c\u5176\u65f6\u95f4\u590d\u6742\u5ea6\u4e3aO(n\/m)(\u5f53m n \/ log(n)\u7684\u65f6\u5019\uff0chash\u8868\u7684\u5e73\u5747\u8868\u73b0\u5c31\u6bd4\u4e8c\u53c9\u6811\u8981\u597d;\u4e14\u5f53m>=n\u65f6\uff0c\u5176\u65f6\u95f4\u590d\u6742\u5ea6\u8d8b\u8fd1\u4e8eO(1)\u3002m\u7684\u503c\u53ef\u4ee5\u505a\u6210\u53ef\u8c03\u6574\u7684\uff0c\u8fd9\u4e5f\u6b63\u663e\u793a\u4e86\u5185\u6838\u7684\u53ef\u5b9a\u5236\u6027\u3002\u4e0d\u8fc7\uff0c\u4e0d\u8981\u76f2\u76ee\u4e50\u89c2\uff0c\u8fd9\u4e00\u5207\u90fd\u662f\u4ee5\u4e00\u4e2a\u8db3\u591f\u597d\u7684hash\u51fd\u6570\u4e3a\u524d\u671f\u7684\u3002<\/p>\n

hash\u51fd\u6570\u7684\u4f18\u52a3<\/strong> <\/p>\n

\u5982\u4f55\u5224\u5b9a\u4e00\u4e2ahash\u51fd\u6570\u7684\u597d\u574f\u5462?
hash\u7684\u4e2d\u6587\u610f\u601d\u662f\u201c\u6563\u5217\u201d\uff0c\u53ef\u89e3\u91ca\u4e3a\uff1a\u5206\u6563\u3002\u4e00\u4e2a\u597d\u7684hash\u51fd\u6570\u5e94\u8be5\u505a\u5230\u5bf9\u6240\u6709\u5143\u7d20\u5e73\u5747\u5206\u6563\u6392\u5217\uff0c\u5c3d\u91cf\u907f\u514d\u6216\u8005\u964d\u4f4e\u4ed6\u4eec\u4e4b\u95f4\u7684\u51b2\u7a81(Collision)\u3002\u6709\u5fc5\u8981\u518d\u6b21\u63d0\u9192\u5927\u5bb6\u7684\u662f\uff0chash\u51fd\u6570\u7684\u9009\u62e9\u5fc5\u987b\u614e\u91cd\uff0c\u5982\u679c\u4e0d\u5e78\u6240\u6709\u7684\u5143\u7d20\u4e4b\u95f4\u90fd\u4ea7\u751f\u4e86\u51b2\u7a81\uff0c\u90a3\u4e48hash\u8868\u5c06\u9000\u5316\u4e3a\u94fe\u8868\uff0c\u5176\u6027\u80fd\u4f1a\u5927\u6253\u6298\u6263\uff0c\u65f6\u95f4\u590d\u6742\u5ea6\u8fc5\u901f\u964d\u4e3aO(n)\uff0c\u7edd\u5bf9\u4e0d\u8981\u5b58\u5728\u4efb\u4f55\u4fa5\u5e78\u5fc3\u7406\uff0c\u56e0\u4e3a\u90a3\u662f\u76f8\u5f53\u5371\u9669\u7684\u3002\u5386\u53f2\u4e0a\u5c31\u51fa\u73b0\u8fc7\u5229\u7528Linux\u5185\u6838hash\u51fd\u6570\u7684\u6f0f\u6d1e\uff0c\u6210\u529f\u6784\u9020\u51fa\u5927\u91cf\u4f7fhash\u8868\u53d1\u751f\u78b0\u649e\u7684\u5143\u7d20\uff0c\u5bfc\u81f4\u7cfb\u7edf\u88abDoS\uff0c\u6240\u4ee5\u76ee\u524d\u5185\u6838\u7684\u5927\u90e8\u5206hash\u51fd\u6570\u90fd\u6709\u4e00\u4e2a\u968f\u673a\u6570\u4f5c\u4e3a\u53c2\u6570\u8fdb\u884c\u63ba\u6742\uff0c\u4ee5\u4f7f\u5176\u6700\u540e\u7684\u503c\u4e0d\u80fd\u6216\u8005\u662f\u4e0d\u6613\u88ab\u9884\u6d4b\u3002\u8fd9\u53c8\u5bf9 hash\u51fd\u6570\u63d0\u51fa\u4e86\u7b2c\u4e8c\u70b9\u5b89\u5168\u65b9\u9762\u7684\u8981\u6c42\uff1ahash\u51fd\u6570\u6700\u597d\u662f\u5355\u5411\u7684\uff0c\u5e76\u4e14\u8981\u7528\u968f\u673a\u6570\u8fdb\u884c\u63ba\u6742\u3002\u63d0\u5230\u5355\u5411\uff0c\u4f60\u4e5f\u8bb8\u4f1a\u60f3\u5230\u5355\u5411\u6563\u5217\u51fd\u6570md4\u548cmd5\uff0c\u5f88\u4e0d\u5e78\u5730\u544a\u8bc9\u4f60\uff0c\u4ed6\u4eec\u662f\u4e0d\u9002\u5408\u7684\uff0c\u56e0\u4e3ahash\u51fd\u6570\u9700\u8981\u6709\u76f8\u5f53\u597d\u7684\u6027\u80fd\u3002
Linux\u5185\u6838\u91cc\u9762\u7528\u7684jhash\u662f\u4e00\u4e2a\u4e45\u7ecf\u8003\u9a8c\uff0c\u5e76\u88ab\u5b9e\u8df5\u8bc1\u660e\u7ecf\u5f97\u8d77\u8003\u9a8c\u7684hash\u51fd\u6570\uff0c\u53ef\u4ee5CPMS(Copy Paste Modify Save)\u4e4b\u3002Jhash\u7684\u4f5c\u8005Bob Jenkins\u5728\u5176\u7f51\u7ad9\u4e0a\u8fd8\u516c\u5e03\u4e86\u8bf8\u5982\u9488\u5bf9\u80fd\u9884\u77e5\u7684\u6570\u636e\u8fdb\u884chash\u7684hash\u51fd\u6570–\u5b8c\u7f8e(perfect)hash\u51fd\u6570\u7b49\u4e00\u7cfb\u5217\u5176\u4ed6hash\u51fd\u6570\u3002
bucket\u7684\u82f1\u6587\u89e3\u91ca\uff1a
Hash table lookup operations are often O(n\/m) (where n is the number of objects in the table and m is the number of buckets), which is close to O(1), especially when the hash function has spread the hashed objects evenly through the hash table, and there are more hash buckets than objects to be stored.<\/p>\n

\u53ef\u4ee5\u8fd9\u6837\u7406\u89e3\uff1a<\/p>\n

\u00b7 \u4e00\u4e2aHASH\u7684\u7ed3\u679c\u6240\u5bf9\u5e94\u7684\u5730\u5740\u53ef\u5b58\u653e\u4e24\u4e2aBUCKET\u3002\u53ef\u89e3\u51b3HASH\u51b2\u7a81\u3002<\/p>\n

\u00b7 \u8981\u5b58\u6570\u636e\u65f6\uff0c\u7b2c\u4e00\u6b21HASH\u5230\u8fd9\u91cc\uff0c\u5728\u7b2c\u4e00\u4e2aBUCKET\u5b58\u653e\u4e00\u4e2a\u6570\u636e\u3002<\/p>\n

\u00b7 \u8981\u5b58\u6570\u636e\u65f6\uff0c\u5f53\u7b2c\u4e8c\u6b21\u56e0\u67d0\u4e9b\u539f\u56e0HASH\u5230\u8fd9\u91cc\u65f6\uff0c\u5728\u7b2c\u4e8c\u4e2aBUCKET\u5b58\u653e\u53e6\u4e00\u4e2a\u6570\u636e\u3002<\/p>\n

\u4e00\u4e2a\u75315\u4e2abuckets\u7ec4\u6210\u7684\u54c8\u5e0c\u8868\uff0c\u91cc\u9762\u67097\u4e2a\u5143\u7d20\uff1a<\/p>\n

\"Linux\u5185\u6838\u4e2d\u7684hash\u4e0ebucket\u7b80\u5355\u4ecb\u7ecd\u63d2\u56fe1\"<\/p>\n

\u7684hash\u51fd\u6570hash_long\u7b49\uff0c\u7528\u4e86golden ratio\u6765\u8ba1\u7b97\u3002\u56e0\u4e3a\u6876(bits)\u7684\u6570\u91cf\u9700\u8981\u7531hash\u51fd\u6570\u548c\u5bf9\u51b2\u7a81\u7684\u671f\u671b\u6765\u51b3\u5b9a\uff0c\u90a3\u4e48\u5bf9\u4e8ehash_long\u8fd9\u6837\u7684hash\u51fd\u6570\uff0c\u6211\u4eec\u600e\u4e48\u786e\u5b9a\u6876\u7684\u6570\u91cf\u5462\uff1f
\u4e00\u822c\u60c5\u51b5\u4e0b\u90fd\u662f\u81ea\u5df1\u6839\u636e\u6570\u636e\u7279\u6027\u6765\u8003\u8651\u4f7f\u7528\u7684 hash \u7b97\u6cd5\uff0c\u4e0d\u662f\u5343\u7bc7\u4e00\u5f8b\u54ac\u6b7b\u4e00\u4e2a\u4e0d\u653e\uff0c\u6bd4\u5982\u5b58\u653e IP \u5730\u5740\u7684 hash table\uff0c\u7528\u4e00\u4e2a 65536 \u7684\u6876\u5c31\u5f88\u597d\uff0c\u628a IP \u7684\u540e 16bit \u4f5c\u4e3a key\u3002\u8fd9\u79cd\u65b9\u6cd5\u7edd\u5bf9\u6bd4 hash_long\u3001jhash \u7b49\u51fd\u6570\u7684\u78b0\u649e\u7387\u4f4e\u3002
\u5176\u5b9e\u5c31\u662f\u8fd9\u4e2a\u754c\u548c\u6027\u80fd\u7684\u6298\u4e2d\u3002\u6211\u53ef\u4ee5\u53d6\u6211\u95ee\u9898\u7a7a\u95f4\u7684\u6700\u5927\u503c\u3002\u8fd9\u6837\u80af\u5b9a\u80fd\u4fdd\u8bc1\u952e\u503c\u5206\u6563\u3002\u4f46\u662f\u8fd9\u6837\u4f1a\u6d6a\u8d39\u5f88\u591a\u7a7a\u95f4\u3002\u7136\u800c\u53d6\u5f97\u592a\u5c0f\uff0c\u53c8\u5f71\u54cd\u67e5\u627e\u6548\u7387\u3002\u611f\u89c9\u8fd8\u662f\u8981\u5728\u8bd5\u9a8c\u4e2d\u8fdb\u884c\u6d4b\u8bd5\u3002\u800c\u4e14hash\u6bd4\u5176\u4ed6\u641c\u7d22\u7684\u6570\u636e\u7ed3\u6784\u7075\u6d3b\u7684\u5730\u65b9\u5c31\u662f\u5b83\u7684\u53ef\u5b9a\u5236\u6027\u3002\u53ef\u4ee5\u6839\u636e\u5177\u4f53\u60c5\u51b5\u8c03\u6574\uff0c\u4ee5\u8fbe\u5230\u6700\u4f18\u7684\u6548\u679c\u3002<\/p>\n

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