{"id":99779,"date":"2026-09-03T10:24:48","date_gmt":"2026-09-03T02:24:48","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/99779.html"},"modified":"2026-09-03T10:24:48","modified_gmt":"2026-09-03T02:24:48","slug":"%e4%b8%ba%e4%bb%80%e4%b9%88%e8%af%b4%e6%9c%89%e5%ba%8f%e6%98%af%e5%ad%98%e5%82%a8%e5%bc%95%e6%93%8e%e7%9a%84%e5%ba%95%e5%b1%82%e7%89%a9%e7%90%86%e5%ae%9a%e5%be%8b%ef%bc%9f%e6%b7%b1","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/99779.html","title":{"rendered":"\u4e3a\u4ec0\u4e48\u8bf4\u201c\u6709\u5e8f\u201d\u662f\u5b58\u50a8\u5f15\u64ce\u7684\u5e95\u5c42\u7269\u7406\u5b9a\u5f8b\uff1f\u6df1\u5ea6\u62c6\u89e3 LevelDB\/RocksDB \u7684 C++ \u63a5\u53e3\u6a21\u578b\uff01"},"content":{"rendered":"

\u5982\u679c\u4f60\u4e60\u60ef\u4e86\u00a0std::unordered_map\u00a0\u6216 Redis \u8fd9\u79cd\u628a\u6570\u636e\u6563\u5217\u843d\u6876\u7684\u601d\u7ef4，\u521d\u6b21\u63a5\u89e6\u5de5\u4e1a\u7ea7\u5d4c\u5165\u5f0f KV \u5f15\u64ce（\u5982 RocksDB \/ LevelDB）\u65f6，\u5927\u6982\u7387\u4f1a\u88ab\u5b83\u7684\u201c\u8d8a\u6743\u201d\u884c\u4e3a\u6253\u4e2a\u63aa\u624b\u4e0d\u53ca：\u4f60\u660e\u660e\u4ece\u672a\u6307\u5b9a\u8fc7\u4efb\u4f55\u6392\u5e8f\u89c4\u5219，\u5b83\u5374\u56fa\u6267\u5730\u91cd\u6392\u4e86\u4f60\u7684\u6bcf\u4e00\u4e2a\u5b57\u8282\u3002<\/p>\n

\u5199\u8fdb 1 \u5230 12 \u7684\u6574\u6570\u5b57\u7b26\u4e32，\u8bfb\u51fa\u6765\u5374\u53d8\u6210\u4e86\u5b57\u5178\u5e8f；\u5982\u679c\u4f60\u76f4\u63a5\u628a\u00a0uint64_t\u00a0\u7684\u5185\u5b58\u6309 Little-Endian\u00a0reinterpret_cast\u00a0\u6254\u8fdb\u00a0Slice，\u539f\u672c\u5355\u8c03\u9012\u589e\u7684\u6570\u503c\u5e8f\u5217\u66f4\u4f1a\u5728\u8de8\u5b57\u8282\u7ffb\u8f6c\u5904\u88ab\u5f7b\u5e95\u641e\u788e\u3002<\/p>\n

\u590d\u73b0\u8fd9\u4e2a\u201c\u4e0d\u8bf7\u81ea\u6765\u201d\u7684\u6392\u5e8f，\u53ea\u9700\u8981\u51e0\u884c\u7eaf\u7cb9\u7684 C++：<\/p>\n

C++<\/p>\n

std::unique_ptr<DB> db;
\nOptions options;
\noptions.create_if_missing = true;
\nStatus s = DB::Open(options, "\/tmp\/kv", &db);<\/p>\n

for (int i = 1; i <= 12; ++i) {
\n \/\/ \u9677\u9631\u5c31\u85cf\u5728 std::to_string(i) \u6784\u9020\u51fa\u7684 Slice \u89c6\u56fe\u4e0e\u9ed8\u8ba4\u4e09\u8def Comparator \u4e2d
\n db->Put(WriteOptions(), std::to_string(i), "v");
\n}<\/p>\n

std::unique_ptr<Iterator> it(db->NewIterator(ReadOptions()));
\nfor (it->SeekToFirst(); it->Valid(); it->Next()) {
\n std::printf("%s ", it->key().ToString().c_str());
\n}
\n\/\/ \u8f93\u51fa：1 10 11 12 2 3 4 5 6 7 8 9<\/p>\n

\u7ecf\u9a8c\u4e30\u5bcc\u7684 C++ \u5de5\u7a0b\u5e08\u4e00\u773c\u5c31\u80fd\u770b\u7a7f\u5e95\u5c42\u662f\u00a0memcmp\u00a0\u5b57\u8282\u5e8f\u5728\u4f5c\u795f\u2014\u2014'1'\u00a0(0x31) \u5929\u7136\u6392\u5728\u00a0'2'\u00a0(0x32) \u524d\u9762\u3002\u4f46\u771f\u6b63\u503c\u5f97\u6df1\u601d\u7684\u95ee\u9898\u4e0d\u662f\u73b0\u8c61\u672c\u8eab，\u800c\u662f\u67b6\u6784\u54f2\u5b66：\u4e3a\u4ec0\u4e48\u8fd9\u7c7b\u5f15\u64ce\u54ea\u6015\u727a\u7272\u5199\u5165\u7075\u6d3b\u6027，\u4e5f\u7edd\u4e0d\u63d0\u4f9b\u4efb\u4f55\u201c\u65e0\u5e8f\u201d\u9009\u9879？<\/p>\n

\u5982\u679c\u4f60\u6b63\u5728\u6216\u8ba1\u5212\u81ea\u7814\u4e00\u4e2a\u9ad8\u6027\u80fd\u5d4c\u5165\u5f0f\u5b58\u50a8\u5f15\u64ce，\u641e\u61c2\u8fd9\u5957\u63a5\u53e3\u6a21\u578b\u4e0e\u80cc\u540e\u7684 C\u5951\u7ea6\u8bbe\u8ba1，\u5c31\u662f\u4f60\u5fc5\u987b\u8de8\u8fc7\u7684\u7b2c\u4e00\u9053\u5206\u6c34\u5cad\u3002\u8fd9\u7bc7\u5c31\u987a\u7740\u4e0a\u9762\u7684\u4ee3\u7801\u5411\u4e0b\u62c6\u89e3，\u9010\u5c42\u5265\u5f00\u73b0\u4ee3 C\u00a0\u5b58\u50a8\u5f15\u64ce\u5728\u63a5\u53e3\u4e0e\u5e95\u5c42\u6a21\u578b\u8bbe\u8ba1\u4e0a\u7684\u786c\u6838\u53d6\u820d\u3002<\/p>\n

\n

1. \u5148\u628a\u5b83\u5f53\u54c8\u5e0c\u8868\u7528，\u76f4\u5230\u8303\u56f4\u626b\u63cf\u628a\u4f60\u62e6\u4e0b\u6765<\/h3>\n

\u649e\u89c1\u987a\u5e8f\u4e4b\u524d，\u5148\u628a\u5b83\u5f53\u6700\u6734\u7d20\u7684\u4e1c\u897f\u4f7f：\u4e00\u4e2a\u80fd\u843d\u76d8\u7684 map\u3002\u4f60\u8111\u5b50\u91cc\u90a3\u4e2a\u00a0std::unordered_map<string, string>\u00a0\u7684\u6a21\u578b，\u5927\u534a\u662f\u5bf9\u7684\u3002\u5199\u4e00\u4e2a\u952e：<\/p>\n

C++<\/p>\n

\/\/ db.h：Set the database entry for "key" to "value".
\n\/\/ If "key" already exists, it will be overwritten.
\nvirtual Status Put(const WriteOptions& options,
\n ColumnFamilyHandle* column_family,
\n const Slice& key, const Slice& value) = 0;<\/p>\n

\u6ce8\u91ca\u7b2c\u4e8c\u884c\u5c31\u662f map \u7684\u8d4b\u503c\u8bed\u4e49：key \u5df2\u5b58\u5728\u5c31\u8986\u76d6\u3002\u6240\u4ee5\u201c\u66f4\u65b0\u201d\u5728\u63a5\u53e3\u5c42\u6839\u672c\u6ca1\u6709\u72ec\u7acb\u7684\u52a8\u8bcd，\u5b83\u5c31\u662f\u518d\u00a0Put\u00a0\u4e00\u6b21\u540c\u4e00\u4e2a key\u3002\u8fd9\u4e00\u70b9\u5148\u8bb0\u4f4f，\u7b2c 5 \u8282\u6211\u4f1a\u544a\u8bc9\u4f60\u5b83\u5728\u5e95\u4e0b\u5176\u5b9e\u6ca1\u8986\u76d6\u4efb\u4f55\u4e1c\u897f\u2014\u2014\u53ea\u662f\u538b\u4e86\u4e00\u5c42\u65b0\u7248\u672c\u4e0a\u53bb，\u4f46\u90a3\u662f\u540e\u8bdd\u3002<\/p>\n

\u53d6\u503c\u8fd9\u4e00\u4fa7，\u6ce8\u610f\u5b83\u7684\u8fd4\u56de\u7ea6\u5b9a：<\/p>\n

C++<\/p>\n

\/\/ db.h：Returns OK on success. Returns NotFound and an empty
\n\/\/ value in "*value" if there is no entry for "key". Returns
\n\/\/ some other non-OK status on error.
\nvirtual Status Get(const ReadOptions& options,
\n ColumnFamilyHandle* column_family, const Slice& key,
\n PinnableSlice* value, std::string* timestamp) = 0;<\/p>\n

\u201c\u67e5\u4e0d\u5230\u201d\u4f1a\u7ed9\u4f60\u4e00\u4e2a\u6b63\u5e38\u7684\u00a0Status::NotFound()\u00a0\u8fd4\u56de\u503c，\u4ece\u4e0d\u629b\u5f02\u5e38\u3002\u8fd9\u8ddf\u00a0std::map::find\u00a0\u8fd4\u56de\u00a0end()\u00a0\u662f\u4e00\u4e2a\u54f2\u5b66\u2014\u2014\u627e\u4e0d\u5230\u662f\u67e5\u8be2\u7684\u5408\u6cd5\u7ed3\u679c\u4e4b\u4e00，\u4e0d\u662f\u9519\u8bef\u3002\u4f60\u73b0\u5728\u5148\u628a\u8fd9\u5f53\u98ce\u683c\u8bb0\u4e0b，\u7b2c 7 \u8282\u6211\u4f1a\u544a\u8bc9\u4f60，\u8fd9\u53f0\u5f15\u64ce\u4ece\u5934\u5230\u5c3e\u4e0d\u7528 C++ \u5f02\u5e38，\u662f\u4e00\u4e2a\u523b\u8fdb\u6574\u5957 API \u7684\u786c\u51b3\u5b9a，Get\u00a0\u53ea\u662f\u5176\u4e2d\u6700\u4e0d\u8d77\u773c\u7684\u4e00\u5904\u3002<\/p>\n

\u5230\u8fd9\u91cc\u4f60\u624b\u91cc\u6709\u4e86\u00a0Put\/Get\/Delete\u00a0\u4e09\u4e2a\u52a8\u4f5c，\u5fc3\u667a\u6a21\u578b\u662f\u201c\u4e00\u4e2a\u843d\u76d8\u7684 map\u201d，\u591f\u7528\u3002\u76f4\u5230\u4f60\u5199\u4e0b\u8fd9\u6837\u4e00\u4e2a\u9700\u6c42：<\/p>\n

\u628a\u00a0user:1000\u00a0\u5230\u00a0user:2000\u00a0\u4e4b\u95f4\u7684\u6240\u6709\u8bb0\u5f55\u62c9\u51fa\u6765\u3002<\/p>\n

std::unordered_map\u00a0\u5e72\u4e0d\u4e86\u8fd9\u4ef6\u4e8b\u3002\u54c8\u5e0c\u8868\u628a key \u6253\u6563\u5230\u6876\u91cc，user:1000\u00a0\u548c\u00a0user:1001\u00a0\u5927\u6982\u7387\u9694\u7740\u534a\u5f20\u8868，\u5b83\u6ca1\u6709\u201c\u4e0b\u4e00\u4e2a key\u201d\u7684\u6982\u5ff5\u3002\u53ef\u5f00\u5934\u90a3\u6bb5\u4ee3\u7801\u91cc，it->Next()\u00a0\u660e\u660e\u5c31\u80fd\u4e00\u4e2a\u63a5\u4e00\u4e2a\u8d70\u4e0b\u53bb，\u800c\u4e14\u8d70\u51fa\u6765\u662f\u6709\u5e8f\u7684\u3002\u5b83\u51ed\u4ec0\u4e48\u80fd\u7ed9\u4f60\u533a\u95f4？\u00a0\u8fd9\u4e2a\u201c\u51ed\u4ec0\u4e48\u201d，\u5c31\u662f\u8fd9\u53f0\u5f15\u64ce\u548c\u4e00\u5f20\u54c8\u5e0c\u8868\u7684\u5206\u6c34\u5cad，\u7b54\u6848\u5728\u7b2c 3 \u8282\u3002\u4f46\u5728\u56de\u7b54\u5b83\u4e4b\u524d，\u6211\u5f97\u5148\u5e26\u4f60\u770b\u5199\u64cd\u4f5c\u2014\u2014\u56e0\u4e3a\u987a\u5e8f\u8fd9\u4ef6\u4e8b，\u7b2c\u4e00\u6b21\u5728\u63a5\u53e3\u4e0a\u9732\u5934\u662f\u5728\u5220\u9664\u91cc\u3002<\/p>\n

2. \u5220\u9664\u53ea\u662f\u8bb0\u4e00\u7b14，\u66f4\u65b0\u53ea\u662f\u538b\u4e00\u5c42<\/h3>\n

\u5148\u770b\u6700\u666e\u901a\u7684\u5220\u9664：<\/p>\n

C++<\/p>\n

\/\/ db.h：Remove the database entry (if any) for "key".
\n\/\/ It is not an error if "key" did not exist in the database.
\nvirtual Status Delete(const WriteOptions& options,
\n ColumnFamilyHandle* column_family,
\n const Slice& key) = 0;<\/p>\n

\u201c\u5220\u4e00\u4e2a\u4e0d\u5b58\u5728\u7684 key \u4e0d\u7b97\u9519\u201d\u2014\u2014\u53c8\u4e00\u6b21，\u63a5\u53e3\u5728\u544a\u8bc9\u4f60\u5b83\u5bf9\u201c\u9519\u8bef\u201d\u7684\u5b9a\u4e49\u5f88\u514b\u5236\u3002\u5220\u9664\u662f\u5e42\u7b49\u7684，\u4f60\u5220\u5341\u904d\u548c\u5220\u4e00\u904d，\u7ed3\u679c\u548c\u8fd4\u56de\u90fd\u4e00\u6837\u3002\u8fd9\u8ddf\u4f60\u81ea\u7814\u5f15\u64ce\u65f6\u7684\u76f4\u89c9\u53ef\u80fd\u51b2\u7a81：\u5f88\u591a\u4eba\u4f1a\u8ba9\u00a0Delete\u00a0\u5728 key \u4e0d\u5b58\u5728\u65f6\u8fd4\u56de\u4e00\u4e2a\u201c\u6ca1\u5220\u5230\u201d\u7684\u4fe1\u53f7，\u7136\u540e\u8c03\u7528\u65b9\u5230\u5904\u5224\u8fd9\u4e2a\u4fe1\u53f7\u3002\u8fd9\u53f0\u5f15\u64ce\u7684\u9009\u62e9\u662f\u2014\u2014\u4e0d\u7ed9\u4f60\u8fd9\u4e2a\u4fe1\u53f7，\u56e0\u4e3a\u5728\u4e00\u4e2a LSM \u7ed3\u6784\u91cc，\u201c\u8fd9\u4e2a key \u73b0\u5728\u5230\u5e95\u5b58\u4e0d\u5b58\u5728\u201d\u672c\u8eab\u5c31\u662f\u4e00\u6b21\u67e5\u8be2\u7684\u6210\u672c，Delete\u00a0\u4e0d\u60f3\u66ff\u4f60\u4ed8\u8fd9\u4e2a\u6210\u672c\u3002<\/p>\n

\u771f\u6b63\u4f1a\u54ac\u4f60\u7684\u662f\u5b83\u65c1\u8fb9\u90a3\u4e2a\u5144\u5f1f，SingleDelete\u3002\u5148\u770b\u4e00\u6bb5\u4f1a\u51fa\u4e8b\u7684\u7528\u6cd5，\u6211\u4eec\u8ba9\u5b83\u5f53\u573a\u574f\u6389：<\/p>\n

C++<\/p>\n

db->Put(WriteOptions(), "k", "v1");
\ndb->Put(WriteOptions(), "k", "v2"); \/\/ \u8986\u76d6，\u5199\u4e86\u7b2c\u4e8c\u904d
\ndb->SingleDelete(WriteOptions(), "k");<\/p>\n

std::string val;
\nStatus s = db->Get(ReadOptions(), "k", &val);
\n\/\/ \u4f60\u4ee5\u4e3a s.IsNotFound()\u3002\u4f46\u8fd9\u91cc\u7684\u884c\u4e3a\u662f\u3010\u672a\u5b9a\u4e49\u3011\u7684：
\n\/\/ val \u53ef\u80fd\u662f "v1"，\u53ef\u80fd NotFound，\u53d6\u51b3\u4e8e\u5e95\u5c42\u538b\u7f29\u5230\u54ea\u4e00\u6b65\u4e86\u3002<\/p>\n

\u6211\u7b2c\u4e00\u6b21\u7528\u00a0SingleDelete\u00a0\u5c31\u683d\u5728\u8fd9\u4e0a\u9762\u3002\u5f53\u65f6\u60f3\u5f53\u7136\u628a\u5b83\u5f53\u6210\u201c\u66f4\u5feb\u7684 Delete\u201d，\u5728\u4e00\u6761\u672c\u8be5\u5e42\u7b49\u7684\u5199\u8def\u5f84\u4e0a\u6df7\u7740\u7528，\u7070\u5ea6\u4e0a\u7ebf\u4e09\u5929\u540e\u6709\u4e00\u6279\u672c\u8be5\u6d88\u5931\u7684 key \u53c8\u8bc8\u5c38\u56de\u6765\u4e86，\u6392\u67e5\u5230\u6700\u540e\u662f\u538b\u7f29\u628a\u4e24\u6761\u5199\u8bb0\u5f55\u7684\u62b5\u6d88\u987a\u5e8f\u641e\u4e71\u4e86\u3002\u539f\u56e0\u5934\u6587\u4ef6\u91cc\u5199\u5f97\u6e05\u6e05\u695a\u695a，\u662f\u6211\u6ca1\u8bfb：<\/p>\n

C++<\/p>\n

\/\/ db.h：If a key is overwritten (by calling Put() multiple times),
\n\/\/ then the result of calling SingleDelete() on this key is undefined.
\n\/\/ SingleDelete() only behaves correctly if there has been only one
\n\/\/ Put() for this key since the previous call to SingleDelete().<\/p>\n

SingleDelete\u00a0\u7684\u5951\u7ea6\u662f：\u4ece\u4e0a\u4e00\u6b21 SingleDelete \u5230\u73b0\u5728，\u8fd9\u4e2a key \u53ea\u88ab Put \u8fc7\u6070\u597d\u4e00\u6b21\u3002\u00a0\u8fdd\u53cd\u4e86\u5c31\u662f\u672a\u5b9a\u4e49\u884c\u4e3a\u3002\u5b83\u4e3a\u4ec0\u4e48\u8fd9\u4e48\u82db\u523b？\u56e0\u4e3a\u5b83\u662f\u4e00\u4e2a\u9488\u5bf9\u7279\u5b9a\u5199\u8d1f\u8f7d\u7684\u6027\u80fd\u4f18\u5316\u2014\u2014\u666e\u901a\u00a0Delete\u00a0\u4f1a\u7559\u4e0b\u4e00\u6761\u201c\u5893\u7891\u201d\u8bb0\u5f55，\u5f97\u7b49\u538b\u7f29\u65f6\u548c\u88ab\u5220\u7684\u90a3\u6761\u771f\u503c\u76f8\u9047\u624d\u80fd\u53cc\u53cc\u6d88\u6389；SingleDelete\u00a0\u627f\u8bfa\u201c\u6211\u4fdd\u8bc1\u53ea\u6709\u4e00\u6761\u771f\u503c\u201d，\u4e8e\u662f\u5893\u7891\u53ef\u4ee5\u7528\u66f4\u4fbf\u5b9c\u7684\u65b9\u5f0f\u62b5\u6d88\u3002\u4f60\u62ff\u8d70\u4e86\u6027\u80fd，\u5c31\u5f97\u66ff\u5b83\u5b88\u4f4f\u90a3\u4e2a\u524d\u63d0\u3002\u5207\u8bb0，\u5207\u8bb0：\u4e00\u4e2a key \u7684\u5199\u8def\u5f84\u4e0a\u53ea\u8981\u6709\u53ef\u80fd Put \u4e24\u6b21，\u5c31\u6c38\u8fdc\u522b\u5bf9\u5b83\u7528 SingleDelete\u3002\u00a0\u8fd9\u662f\u81ea\u7814\u5f15\u64ce\u6700\u5bb9\u6613\u6284\u9519\u7684\u4e00\u7c7b\u63a5\u53e3\u2014\u2014\u628a\u522b\u4eba\u4e3a\u7279\u5b9a\u524d\u63d0\u8bbe\u8ba1\u7684\u5feb\u8def\u5f84，\u5f53\u6210\u901a\u7528\u8def\u5f84\u4e71\u94fa\u3002<\/p>\n

\u5199\u64cd\u4f5c\u8fd8\u6709\u4e00\u4e2a\u4f60\u8fdf\u65e9\u8981\u63d0\u4f9b\u7684\u80fd\u529b：\u628a\u591a\u4e2a\u5199\u6253\u6210\u4e00\u4e2a\u539f\u5b50\u5305\u3002\u770b\u8fd9\u6bb5\u2014\u2014\u4e00\u6b21\u5220\u4e00\u4e2a key\u3001\u52a0\u4e24\u4e2a key，\u8981\u4e48\u5168\u6210\u3001\u8981\u4e48\u5168\u4e0d\u6210：<\/p>\n

C++<\/p>\n

WriteBatch batch;
\nbatch.Put(handles[0], Slice("key2"), Slice("value2"));
\nbatch.Put(handles[1], Slice("key3"), Slice("value3"));
\nbatch.Delete(handles[0], Slice("key"));
\nStatus s = db->Write(WriteOptions(), &batch);<\/p>\n

WriteBatch\u00a0\u628a\u82e5\u5e72\u4e2a\u00a0Put\/Delete\u00a0\u6512\u6210\u4e00\u6279，Write\u00a0\u4e00\u6b21\u6027\u539f\u5b50\u843d\u76d8\u3002\u6709\u610f\u601d\u7684\u662f，\u5355\u4e2a\u00a0Put\u00a0\u5176\u5b9e\u4e5f\u662f\u8d70\u00a0Write\u00a0\u7684\u2014\u2014\u5b83\u5c31\u662f\u4e00\u4e2a\u53ea\u88c5\u4e86\u4e00\u6761\u64cd\u4f5c\u7684 batch，\u63a5\u53e3\u5c42\u6839\u672c\u6ca1\u6709\u7b2c\u4e8c\u6761\u5199\u8def\u5f84\u3002\u539f\u5b50\u6027\u4ece\u54ea\u6765？\u4ece\u90a3\u6761\u9884\u5199\u65e5\u5fd7（WAL）：\u6574\u6279\u64cd\u4f5c\u5148\u4f5c\u4e3a\u4e00\u6761\u8bb0\u5f55\u987a\u5e8f\u8ffd\u52a0\u8fdb\u65e5\u5fd7，\u65e5\u5fd7\u843d\u76d8\u6210\u529f\u8fd9\u6279\u624d\u7b97\u6570；\u4e2d\u9014\u5d29\u4e86，\u91cd\u542f\u65f6\u8981\u4e48\u6574\u6761\u65e5\u5fd7\u8fd8\u5728\u3001\u6574\u6279\u91cd\u653e，\u8981\u4e48\u6574\u6761\u6ca1\u5199\u5168\u3001\u6574\u6279\u5f53\u6ca1\u53d1\u751f\u8fc7\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u7684\u539f\u5b50\u6027\u5730\u57fa，\u51e0\u4e4e\u4e00\u5b9a\u662f\u8fd9\u6761\u201c\u5148\u987a\u5e8f\u5199\u65e5\u5fd7\u3001\u518d\u6539\u5185\u5b58\u7ed3\u6784\u201d\u7684\u8def\u5b50\u2014\u2014\u800c\u987a\u5e8f\u5199\u65e5\u5fd7\u53c8\u662f\u4e00\u6b21\u5bf9\u78c1\u76d8\u6781\u53cb\u597d\u7684\u987a\u5e8f IO，\u548c\u6709\u5e8f\u7ed3\u6784\u90a3\u80a1\u201c\u628a\u968f\u673a\u63b0\u6210\u987a\u5e8f\u201d\u7684\u6c14\u8d28\u4e00\u8109\u76f8\u627f\u3002<\/p>\n

\u73b0\u5728\u770b\u987a\u5e8f\u7b2c\u4e00\u6b21\u9732\u5934\u7684\u5730\u65b9，\u533a\u95f4\u5220\u9664：<\/p>\n

C++<\/p>\n

\/\/ db.h：Removes the database entries in the range
\n\/\/ ["begin_key", "end_key"), i.e., including "begin_key" and
\n\/\/ excluding "end_key".
\n\/\/ If "end_key" comes before "start_key" according to the user's
\n\/\/ comparator, a `Status::InvalidArgument` is returned.
\nvirtual Status DeleteRange(const WriteOptions& options,
\n ColumnFamilyHandle* column_family,
\n const Slice& begin_key, const Slice& end_key);<\/p>\n

\u4e24\u4e2a\u7ec6\u8282\u503c\u5f97\u505c\u4e00\u4e0b\u3002\u4e00\u662f\u534a\u5f00\u533a\u95f4\u00a0[begin, end)，\u542b\u5de6\u4e0d\u542b\u53f3\u2014\u2014\u8fd9\u662f\u6240\u6709\u533a\u95f4\u63a5\u53e3\u7684\u8001\u89c4\u77e9，\u548c STL \u8fed\u4ee3\u5668\u4e00\u4e2a\u7ea6\u5b9a，\u597d\u5904\u662f\u76f8\u90bb\u533a\u95f4\u80fd\u65e0\u7f1d\u62fc\u63a5，[a,b)\u00a0\u52a0\u00a0[b,c)\u00a0\u6b63\u597d\u7b49\u4e8e\u00a0[a,c)，\u4e0d\u91cd\u4e0d\u6f0f\u3002\u4e8c\u662f\u90a3\u53e5\u00a0if "end_key" comes before "start_key" according to the user's comparator\u2014\u2014\u201caccording to the user's comparator\u201d\u3002\u5230\u8fd9\u91cc，\u4f60\u5df2\u7ecf\u8eb2\u4e0d\u5f00\u90a3\u4e2a\u95ee\u9898\u4e86：\u8fd9\u53f0\u5f15\u64ce\u5224\u65ad\u8c01\u5728\u524d\u8c01\u5728\u540e，\u9760\u7684\u662f\u4e00\u4e2a\u53eb comparator \u7684\u4e1c\u897f，\u800c\u4e14\u662f\u201cuser's\u201d，\u53ef\u4ee5\u7531\u4f60\u6362\u3002\u533a\u95f4\u5220\u9664\u53ea\u662f\u7b2c\u4e00\u4e2a\u628a\u5b83\u903c\u5230\u53f0\u9762\u4e0a\u7684\u63a5\u53e3，\u63a5\u4e0b\u6765\u6bcf\u4e00\u4e2a\u8ddf\u201c\u8303\u56f4\u201d\u201c\u987a\u5e8f\u201d\u201c\u524d\u7f00\u201d\u6cbe\u8fb9\u7684\u529f\u80fd，\u5e95\u4e0b\u90fd\u7ad9\u7740\u5b83\u3002<\/p>\n

3. \u987a\u5e8f\u662f\u8c01\u5b9a\u7684：\u4e09\u8def\u6bd4\u8f83\u51fd\u6570\u5c31\u662f\u8fd9\u53f0\u5f15\u64ce\u7684\u201c\u7269\u7406\u5b9a\u5f8b\u201d<\/h3>\n

\u56de\u5230\u5f00\u5934\u90a3\u4e2a\u8c1c：1 10 11 12 2\u3002\u73b0\u5728\u628a\u5b9a\u4e49\u987a\u5e8f\u7684\u90a3\u4e2a\u5bf9\u8c61\u8bf7\u51fa\u6765\u3002\u5b83\u5728 comparator.h \u91cc，\u63a5\u53e3\u5c0f\u5f97\u53ef\u601c：<\/p>\n

C++<\/p>\n

\/\/ comparator.h
\nclass CompareInterface {
\n public:
\n \/\/ Three-way comparison. Returns value:
\n \/\/ < 0 iff "a" < "b",
\n \/\/ == 0 iff "a" == "b",
\n \/\/ > 0 iff "a" > "b"
\n virtual int Compare(const Slice& a, const Slice& b) const = 0;
\n};<\/p>\n

\u4e00\u4e2a\u4e09\u8def\u6bd4\u8f83\u51fd\u6570，\u8fd4\u56de\u8d1f \/ \u96f6 \/ \u6b63\u3002\u5c31\u8fd9\u4e48\u4e00\u4e2a\u7eaf\u865a\u51fd\u6570，\u5b9a\u4e49\u4e86\u6574\u53f0\u5f15\u64ce\u91cc\u201c\u987a\u5e8f\u201d\u8fd9\u4e2a\u8bcd\u7684\u5168\u90e8\u542b\u4e49\u3002\u5b83\u4e0a\u9762\u90a3\u5c42\u00a0Comparator\u00a0\u7c7b\u7684\u6ce8\u91ca，\u628a\u8bdd\u8bf4\u5230\u4e86\u5934：<\/p>\n

C++<\/p>\n

\/\/ comparator.h：A Comparator object provides a total order across
\n\/\/ slices that are used as keys in an sstable or a database.<\/p>\n

\u5168\u5e8f（total order）\u3002\u00a0\u4efb\u610f\u4e24\u4e2a key，\u8981\u4e48\u76f8\u7b49，\u8981\u4e48\u4e00\u4e2a\u4e25\u683c\u5728\u53e6\u4e00\u4e2a\u524d\u9762，\u6ca1\u6709\u201c\u65e0\u6cd5\u6bd4\u8f83\u201d\u8fd9\u79cd\u60c5\u51b5\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u65f6\u5982\u679c\u6253\u7b97\u652f\u6301\u8303\u56f4\u626b\u63cf，\u8fd9\u56db\u4e2a\u5b57\u5c31\u662f\u4f60\u5fc5\u987b\u5148\u4ea4\u51fa\u7684\u4e1c\u897f：\u6570\u5b66\u610f\u4e49\u4e0a\u7684\u5168\u5e8f，\u4efb\u610f\u4e24\u4e2a key \u90fd\u80fd\u6bd4\u51fa\u5148\u540e，\u5426\u5219\u5e95\u5c42\u7684\u6709\u5e8f\u7ed3\u6784\u4f1a\u5728\u67d0\u4e24\u4e2a key \u4e0a\u76f4\u63a5\u5d29\u6389\u3002<\/p>\n

\u90a3\u9ed8\u8ba4\u90a3\u5957\u987a\u5e8f\u662f\u54ea\u6765\u7684？comparator.h \u5e95\u90e8：<\/p>\n

C++<\/p>\n

\/\/ comparator.h：Return a builtin comparator that uses lexicographic
\n\/\/ ordering on unsigned bytes, so the empty string is ordered before
\n\/\/ everything else and a sufficiently long string of \\\\xFF orders
\n\/\/ after anything.
\nconst Comparator* BytewiseComparator();<\/p>\n

\u6309\u65e0\u7b26\u53f7\u5b57\u8282\u505a\u5b57\u5178\u5e8f\u3002\u00a0\u73b0\u5728\u5f00\u5934\u90a3\u4e2a\u73b0\u8c61\u4e00\u79d2\u5c31\u901a\u4e86："10"\u00a0\u548c\u00a0"2"\u00a0\u662f\u4e24\u4e32\u5b57\u8282，\u9010\u5b57\u8282\u6bd4，'1'(0x31) \u649e\u00a0'2'(0x32)，\u524d\u8005\u5c0f，\u6240\u4ee5\u00a0"12" < "2"\u3002\u5b83\u538b\u6839\u4e0d\u77e5\u9053\u4f60\u5fc3\u91cc\u90a3\u662f\u6574\u6570，\u5b83\u773c\u91cc\u53ea\u6709\u5b57\u8282\u3002<\/p>\n

\u8fd9\u5f15\u51fa\u81ea\u7814\u5f15\u64ce\u91cc\u6700\u7ecf\u5178\u7684\u4e00\u4e2a\u5751，\u6211\u4eec\u8ba9\u5b83\u5f53\u573a\u574f\u7ed9\u4f60\u770b\u3002\u5047\u8bbe\u4f60\u5acc\u5b57\u7b26\u4e32 key \u5360\u5730\u65b9，\u6539\u6210\u628a\u539f\u751f\u00a0int\u00a0\u76f4\u63a5\u62f7\u8fdb key：<\/p>\n

C++<\/p>\n

int k1 = 1, k2 = 256;
\ndb->Put(WriteOptions(),
\n Slice(reinterpret_cast<char*>(&k1), sizeof(int)), "a");
\ndb->Put(WriteOptions(),
\n Slice(reinterpret_cast<char*>(&k2), sizeof(int)), "b");
\n\/\/ x86 \u662f\u5c0f\u7aef：
\n\/\/ 1 \u5728\u5185\u5b58\u91cc\u662f 01 00 00 00
\n\/\/ 256 \u5728\u5185\u5b58\u91cc\u662f 00 01 00 00
\n\/\/ \u6309\u5b57\u8282\u6bd4：256 \u7684\u9996\u5b57\u8282 0x00 < 1 \u7684\u9996\u5b57\u8282 0x01
\n\/\/ \u4e8e\u662f\u8303\u56f4\u626b\u63cf\u91cc，256 \u6392\u5728\u4e86 1 \u524d\u9762\u3002<\/p>\n

\u5728\u5c0f\u7aef\u673a\u5668\u4e0a，int\u00a0\u7684\u4f4e\u5b57\u8282\u5728\u524d，256\u00a0\u7684\u5b57\u8282\u5e8f\u5217\u00a000 01 00 00\u00a0\u9996\u5b57\u8282\u662f 0，\u6bd4\u00a01\u00a0\u7684\u00a001 00 00 00\u00a0\u8fd8\u5c0f，\u4e8e\u662f 256 \u88ab\u6392\u5230\u4e86 1 \u524d\u9762\u2014\u2014\u4f60\u7684\u6570\u503c\u987a\u5e8f\u88ab\u5b57\u8282\u5e8f\u5f7b\u5e95\u6253\u4e71\u3002\u4fee\u6cd5\u53ea\u6709\u4e00\u4e2a：key \u91cc\u7684\u6574\u6570\u5fc5\u987b\u6309\u5927\u7aef\u7f16\u7801\u518d\u5b58，\u8ba9\u9ad8\u4f4d\u5b57\u8282\u843d\u5728\u524d\u9762，\u5b57\u8282\u5b57\u5178\u5e8f\u624d\u548c\u6570\u503c\u987a\u5e8f\u5bf9\u9f50\u3002\u8fd9\u662f\u6bcf\u4e00\u4e2a\u7528\u6709\u5e8f KV \u5b58\u6574\u6570\u4e3b\u952e\u7684\u4eba\u90fd\u5fc5\u987b\u8fc7\u7684\u4e00\u9053\u574e，\u8fc7\u4e0d\u53bb，\u4f60\u7684\u8303\u56f4\u626b\u63cf\u5c31\u662f\u9519\u7684，\u800c\u4e14\u9519\u5f97\u6084\u65e0\u58f0\u606f\u2014\u2014\u6ca1\u6709\u62a5\u9519，\u53ea\u6709\u987a\u5e8f\u4e0d\u5bf9\u3002\u9762\u8bd5\u65f6\u5982\u679c\u6709\u4eba\u8ba9\u4f60\u7528\u6709\u5e8f KV \u5b58\u4e00\u5f20\u6309\u65f6\u95f4\u6392\u5e8f\u7684\u8868，\u7b2c\u4e00\u53e5\u5c31\u8be5\u95ee\u201c\u65f6\u95f4\u6233\u600e\u4e48\u7f16\u7801\u201d，\u7b54\u4e0d\u51fa\u5927\u7aef，\u8fd9\u9053\u9898\u57fa\u672c\u5c31\u5e9f\u4e86\u3002<\/p>\n

\u6bd4\u201c\u987a\u5e8f\u9519\u4e86\u201d\u66f4\u72e0\u7684，\u662f\u201c\u987a\u5e8f\u53d8\u4e86\u5374\u6ca1\u4eba\u544a\u8bc9\u4f60\u201d\u3002\u770b\u00a0Comparator\u00a0\u7684\u00a0Name()：<\/p>\n

C++<\/p>\n

\/\/ comparator.h：The name of the comparator. Used to check for
\n\/\/ comparator mismatches (i.e., a DB created with one comparator is
\n\/\/ accessed using a different comparator).
\n\/\/ The client of this package should switch to a new name whenever
\n\/\/ the comparator implementation changes in a way that will cause the
\n\/\/ relative ordering of any two keys to change.
\nconst char* Name() const override = 0;<\/p>\n

\u6bd4\u8f83\u5668\u7684\u540d\u5b57\u4f1a\u88ab\u5199\u8fdb\u5e93\u91cc\u6301\u4e45\u5316\u3002\u4e0b\u6b21\u5f00\u5e93，\u5f15\u64ce\u62ff\u5f53\u524d\u6bd4\u8f83\u5668\u7684\u540d\u5b57\u548c\u5e93\u91cc\u5b58\u7684\u90a3\u4e2a\u6838\u5bf9，\u5bf9\u4e0d\u4e0a\u5c31\u62d2\u7edd\u6253\u5f00\u3002\u4e3a\u4ec0\u4e48\u8981\u8fd9\u4e48\u9632\u7740\u4f60？\u56e0\u4e3a\u987a\u5e8f\u4e0d\u662f\u67e5\u8be2\u65f6\u624d\u7528\u4e00\u4e0b\u7684\u8fd0\u884c\u671f\u53c2\u6570，\u5b83\u523b\u8fdb\u4e86\u78c1\u76d8\u4e0a\u6bcf\u4e00\u4e2a\u6709\u5e8f\u6570\u636e\u5757\u7684\u7269\u7406\u5e03\u5c40\u3002\u6574\u53f0\u5f15\u64ce\u7684\u78c1\u76d8\u7ed3\u6784\u3001\u7d22\u5f15\u5757\u3001\u4e8c\u5206\u67e5\u627e，\u5168\u90fd\u5efa\u7acb\u5728\u201c\u5e93\u91cc\u7684 key \u662f\u6309\u67d0\u4e2a\u56fa\u5b9a\u987a\u5e8f\u7801\u597d\u7684\u201d\u8fd9\u4e2a\u524d\u63d0\u4e0a\u3002\u4f60\u4eca\u5929\u7528\u5927\u7aef\u987a\u5e8f\u7801\u4e86\u4e00\u767e\u4e07\u6761\u6570\u636e，\u660e\u5929\u6362\u4e2a\u6bd4\u8f83\u5668\u6539\u6210\u5c0f\u7aef，\u90a3\u4e00\u767e\u4e07\u6761\u7684\u7269\u7406\u6392\u5217\u77ac\u95f4\u5168\u9519\u2014\u2014\u4e8c\u5206\u67e5\u627e\u4f1a\u6307\u5411\u9519\u8bef\u7684\u5757，\u626b\u63cf\u4f1a\u6f0f\u6389\u672c\u8be5\u5728\u533a\u95f4\u91cc\u7684 key\u3002\u6240\u4ee5\u5f15\u64ce\u7684\u6001\u5ea6\u662f：\u6362\u6bd4\u8f83\u5668\u7b49\u4e8e\u6362\u4e86\u4e00\u4e2a\u6570\u636e\u5e93，\u5b83\u5b81\u53ef\u62d2\u7edd\u5f00\u5e93\u4e5f\u4e0d\u8ba9\u4f60\u5728\u4e00\u4e2a\u987a\u5e8f\u4e0a\u5199\u3001\u53e6\u4e00\u4e2a\u987a\u5e8f\u4e0a\u8bfb\u3002<\/p>\n

\u8fd9\u5c31\u662f\u6211\u8bf4\u201c\u4e09\u8def\u6bd4\u8f83\u51fd\u6570\u662f\u8fd9\u53f0\u5f15\u64ce\u7684\u7269\u7406\u5b9a\u5f8b\u201d\u7684\u610f\u601d\u3002\u5b83\u662f\u4e00\u6761\u4e00\u65e6\u9009\u5b9a\u3001\u5199\u4e0b\u7b2c\u4e00\u4e2a key \u5c31\u51bb\u7ed3\u7684\u4e0d\u53d8\u91cf，\u8fd0\u884c\u671f\u52a8\u5b83\u4e0d\u5f97\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u65f6\u5bf9\u5b83\u7684\u552f\u4e00\u6b63\u786e\u6001\u5ea6\u662f：\u5f00\u5de5\u7b2c\u4e00\u4ef6\u4e8b\u5c31\u5b9a\u6b7b\u6bd4\u8f83\u51fd\u6570，\u5e76\u4e14\u7ed9\u5b83\u4e00\u4e2a\u7248\u672c\u5316\u7684\u540d\u5b57，\u5f80\u540e\u4f46\u51e1\u6539\u52a8\u4e86\u4efb\u610f\u4e24\u4e2a key \u7684\u76f8\u5bf9\u987a\u5e8f，\u5c31\u6362\u540d\u5b57\u3001\u5c31\u5f53\u6210\u4e00\u4e2a\u65b0\u5e93\u6765\u8fc1\u79fb\u3002\u00a0\u987a\u5e8f\u5373\u8eab\u4efd\u3002<\/p>\n

\u6bd4\u8f83\u5668\u8fd8\u6709\u4e24\u4e2a\u4e0d\u8d77\u773c\u7684\u65b9\u6cd5，\u987a\u5e26\u70b9\u7834，\u5b83\u4eec\u66b4\u9732\u4e86\u987a\u5e8f\u6e17\u900f\u5f97\u6709\u591a\u6df1：<\/p>\n

C++<\/p>\n

\/\/ comparator.h：Advanced functions: these are used to reduce the
\n\/\/ space requirements for internal data structures like index blocks.
\nvirtual void FindShortestSeparator(std::string* start,
\n const Slice& limit) const = 0;
\nvirtual void FindShortSuccessor(std::string* key) const = 0;<\/p>\n

\u5f15\u64ce\u4f1a\u62ff\u6bd4\u8f83\u5668\u53bb\u627e\u201c\u4e24\u4e2a key \u4e4b\u95f4\u4e00\u4e2a\u5c3d\u91cf\u77ed\u7684\u5206\u9694\u4e32\u201d，\u7528\u5b83\u5f53\u7d22\u5f15\u5757\u7684\u8fb9\u754c，\u7701\u7a7a\u95f4\u3002\u4e5f\u5c31\u662f\u8bf4，\u6bd4\u8f83\u5668\u4e0d\u53ea\u5728\u4f60\u67e5\u8be2\u65f6\u88ab\u8c03\u7528，\u5b83\u8fd8\u5728\u540e\u53f0\u53c2\u4e0e\u5851\u9020\u7d22\u5f15\u7684\u7269\u7406\u5f62\u6001\u3002\u8fd9\u6761\u7ebf\u4f60\u73b0\u5728\u6709\u4e2a\u5370\u8c61\u5c31\u884c\u2014\u2014\u5b83\u8bf4\u660e\u7684\u662f\u540c\u4e00\u4ef6\u4e8b：\u987a\u5e8f\u8fd9\u4e2a\u4e1c\u897f，\u4ece\u4f60\u7684 key \u7f16\u7801，\u4e00\u8def\u6e17\u5230\u6700\u5e95\u5c42\u7684\u78c1\u76d8\u7ed3\u6784\u91cc，\u6ca1\u6709\u4e00\u5c42\u80fd\u7ed5\u5f00\u5b83\u3002<\/p>\n

\u987a\u5e8f\u8fd8\u6709\u4e00\u5c42\u4f60\u73b0\u5728\u672a\u5fc5\u7528\u5f97\u4e0a\u3001\u5374\u51b3\u5b9a\u4e86\u201c\u6709\u7248\u672c\u201d\u600e\u4e48\u843d\u5730\u7684\u4e1c\u897f\u2014\u2014\u65f6\u95f4\u6233\u3002\u56de\u5934\u770b\u00a0Compare\u00a0\u7684\u5b8c\u6574\u6ce8\u91ca，\u5b83\u591a\u8bf4\u4e86\u4e00\u53e5：<\/p>\n

C++<\/p>\n

\/\/ comparator.h：Note that Compare(a, b) also compares timestamp if
\n\/\/ timestamp size is non-zero. For the same user key with different
\n\/\/ timestamps, larger (newer) timestamp comes first.<\/p>\n

\u540c\u4e00\u4e2a\u7528\u6237 key，\u5e26\u4e0d\u540c\u65f6\u95f4\u6233\u65f6，\u66f4\u65b0\u7684\u90a3\u4e2a\u6392\u5728\u524d\u9762\u3002\u8fd9\u53e5\u8bdd\u628a\u201c\u987a\u5e8f\u201d\u548c\u201c\u7248\u672c\u201d\u710a\u5728\u4e86\u4e00\u8d77：\u6bd4\u8f83\u5668\u4e0d\u53ea\u88c1\u5b9a key \u4e0e key \u4e4b\u95f4\u8c01\u5148\u8c01\u540e，\u8fd8\u88c1\u5b9a\u540c\u4e00\u4e2a key \u7684\u591a\u4e2a\u7248\u672c\u91cc\u8c01\u5148\u8c01\u540e\u2014\u2014\u800c\u201c\u65b0\u7248\u672c\u6392\u5728\u524d\u201d\u6b63\u662f\u8303\u56f4\u626b\u63cf\u9ed8\u8ba4\u8bfb\u5230\u6700\u65b0\u503c\u7684\u5e95\u5c42\u539f\u56e0\u3002\u8fd9\u4e5f\u662f\u4e3a\u4ec0\u4e48\u5185\u7f6e\u7684\u5e26\u65f6\u95f4\u6233\u6bd4\u8f83\u5668\u8981\u4e13\u95e8\u89c4\u5b9a\u201c\u5168\u96f6\u5b57\u8282\u662f\u6700\u5c0f（\u6700\u65e7）\u65f6\u95f4\u6233\u3001\u5168\u4e00\u5b57\u8282\u662f\u6700\u5927（\u6700\u65b0）\u201d：\u7248\u672c\u4e4b\u95f4\u7684\u5148\u540e，\u4e5f\u5f97\u662f\u4e00\u4e2a\u4f60\u80fd\u5728\u5b57\u8282\u5c42\u9762\u7b97\u5f97\u6e05\u7684\u5168\u5e8f\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u8981\u652f\u6301\u591a\u7248\u672c\u8bfb，\u8fd9\u6761\u7ed5\u4e0d\u5f00\u2014\u2014\u7248\u672c\u53f7\u662f\u6392\u5e8f\u952e\u7684\u4e00\u90e8\u5206，\u4e0d\u662f\u6302\u5728 value \u4e0a\u7684\u4e00\u5757\u5143\u6570\u636e\u3002\u7b2c 10 \u8282\u6211\u4f1a\u5e26\u4f60\u770b\u8fd9\u4e2a\u7248\u672c\u53f7\u600e\u4e48\u53d8\u6210\u5feb\u7167\u3001\u600e\u4e48\u51b3\u5b9a\u4e00\u6761\u65e7\u6570\u636e\u80fd\u4e0d\u80fd\u88ab\u56de\u6536\u3002<\/p>\n

4. \u6709\u5e8f Map \u548c\u65e0\u5e8f Hash，\u5206\u53c9\u7684\u662f\u6574\u53f0\u5f15\u64ce<\/h3>\n

\u73b0\u5728\u6b63\u9762\u56de\u7b54\u7b2c 1 \u8282\u7559\u4e0b\u7684\u201c\u5b83\u51ed\u4ec0\u4e48\u80fd\u7ed9\u4f60\u533a\u95f4\u201d\u3002\u628a\u6709\u5e8f\u7ed3\u6784\u548c\u54c8\u5e0c\u8868\u5e76\u6392\u653e，\u5582\u540c\u4e00\u4e2a\u64cd\u4f5c，\u770b\u5b83\u4eec\u5728\u54ea\u4e00\u6b65\u5206\u53c9\u3002<\/p>\n

\u70b9\u67e5\u8fd9\u4e00\u5173，\u4e24\u8005\u6253\u5e73，\u751a\u81f3\u54c8\u5e0c\u8fd8\u8d62\u4e00\u70b9\u3002\u54c8\u5e0c\u8868\u7406\u8bba\u4e0a\u662f\u5747\u644a\u00a0O(1)，\u6709\u5e8f\u7ed3\u6784\u662f\u00a0O(log n)\u00a0\u7684\u4e8c\u5206\u3002\u5dee\u8ddd\u5728\u8303\u56f4\u626b\u63cf：<\/p>\n\n\n\n

\u64cd\u4f5c<\/p>\n

\u65e0\u5e8f Hash<\/p>\n

\u6709\u5e8f\u7ed3\u6784<\/p>\n<\/tr>\n

\n\n
\n

\u70b9\u67e5\u00a0user:1500<\/p>\n<\/td>\n

\n

\u7b97\u54c8\u5e0c\u5b9a\u6876，O(1)\u00a0\u5f88\u5feb<\/p>\n<\/td>\n

\n

\u4e8c\u5206\u5b9a\u4f4d，O(log n)<\/p>\n<\/td>\n<\/tr>\n

\n

\u626b\u00a0[user:1000, user:2000)<\/p>\n<\/td>\n

\n

\u76f8\u90bb key \u6563\u843d\u5404\u5904，\u53ea\u80fd\u5168\u8868\u626b\u4e00\u904d\u00a0O(n)<\/p>\n<\/td>\n

\n

\u5b9a\u4f4d\u8d77\u70b9\u00a0O(log n)，\u518d\u987a\u7740\u8d70\u00a0O(k)（k\u00a0\u4e3a\u547d\u4e2d\u6761\u6570）<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u54c8\u5e0c\u8868\u505a\u8303\u56f4\u626b\u63cf\u8981\u9000\u5316\u6210\u5168\u8868\u626b\u63cf\u52a0\u8fc7\u6ee4，\u56e0\u4e3a\u5b83\u4e3b\u52a8\u628a key \u7684\u90bb\u63a5\u5173\u7cfb\u6253\u6563\u4e86\u2014\u2014\u8fd9\u6b63\u662f\u5b83\u00a0O(1)\u00a0\u70b9\u67e5\u7684\u4ee3\u4ef7\u6765\u6e90\u3002\u6709\u5e8f\u7ed3\u6784\u53cd\u8fc7\u6765，\u7528\u00a0O(log n)\u00a0\u7684\u70b9\u67e5，\u6362\u6765\u4e86\u201ckey \u5728\u7269\u7406\u4e0a\u5c31\u662f\u6328\u7740\u6392\u7684\u201d，\u4e8e\u662f\u8303\u56f4\u626b\u63cf\u80fd\u5148\u4e8c\u5206\u5b9a\u4f4d\u5230\u8d77\u70b9，\u518d\u987a\u7740\u5f80\u4e0b\u8d70\u3002\u627f\u63a5\u8fd9\u4e2a\u80fd\u529b\u7684，\u5c31\u662f\u5f00\u5934\u90a3\u4e2a\u00a0Iterator\u3002\u770b\u5b83\u7684\u6e38\u6807\u63a5\u53e3，\u5728 iterator_base.h \u91cc：<\/p>\n

C++<\/p>\n

\/\/ iterator_base.h
\n\/\/ Position at the first key in the source that at or past target.
\nvirtual void Seek(const Slice& target) = 0;
\n\/\/ Moves to the next entry in the source. REQUIRES: Valid()
\nvirtual void Next() = 0;
\nvirtual bool Valid() const = 0;
\nvirtual Slice key() const = 0;<\/p>\n

Seek(target)\u00a0\u7684\u8bed\u4e49\u662f\u201c\u505c\u5728\u7b2c\u4e00\u4e2a\u5927\u4e8e\u7b49\u4e8e target \u7684 key \u4e0a\u201d\u3002\u8fd9\u4e2a\u201c\u5927\u4e8e\u7b49\u4e8e\u201d，\u7528\u7684\u5c31\u662f\u7b2c 3 \u8282\u90a3\u4e2a\u6bd4\u8f83\u5668\u3002\u6240\u4ee5\u8303\u56f4\u626b\u63cf\u00a0["user:1000","user:2000")\u00a0\u843d\u5230\u63a5\u53e3\u4e0a，\u5c31\u662f\u00a0Seek("user:1000")\u00a0\u5b9a\u4f4d\u8d77\u70b9，\u7136\u540e\u00a0Next()\u00a0\u4e00\u8def\u8d70，\u6bcf\u6b65\u7528\u6bd4\u8f83\u5668\u5224\u65ad\u6709\u6ca1\u6709\u8d8a\u8fc7\u00a0"user:2000"\u00a0\u8fd9\u4e2a\u53f3\u754c\u3002\u6709\u5e8f\u6027\u5728\u8fd9\u91cc\u5151\u73b0\u6210\u4e86\u771f\u91d1\u767d\u94f6\u7684\u80fd\u529b：\u4e00\u6b21\u4e8c\u5206\u52a0\u4e00\u6bb5\u987a\u5e8f\u8bfb，\u800c\u4e0d\u662f\u626b\u5168\u5e93\u3002<\/p>\n

\u8fd9\u4e2a\u5206\u53c9\u4e0d\u6b62\u505c\u5728\u67e5\u8be2\u63a5\u53e3\u4e0a，\u5b83\u4e00\u8def\u5411\u4e0b\u51b3\u5b9a\u4e86\u6574\u53f0\u5f15\u64ce\u7684\u5f62\u6001，\u8fd9\u624d\u662f\u6211\u8981\u4f60\u8bb0\u4f4f\u7684\u91cd\u70b9：<\/p>\n

    \n
  • \n

    \u78c1\u76d8 IO \u5f62\u6001\u3002\u00a0\u6709\u5e8f\u610f\u5473\u7740\u76f8\u90bb key \u5927\u6982\u7387\u843d\u5728\u540c\u4e00\u4e2a\u78c1\u76d8\u5757\u3001\u540c\u4e00\u6b21\u9884\u8bfb\u91cc\u3002\u8303\u56f4\u626b\u63cf\u53d8\u6210\u4e00\u6bb5\u63a5\u8fd1\u987a\u5e8f\u8bfb\u7684 IO，\u8fd9\u5bf9\u673a\u68b0\u76d8\u662f\u6570\u91cf\u7ea7\u7684\u5dee\u5f02，\u5bf9 SSD \u4e5f\u7701\u4e0b\u5927\u91cf\u968f\u673a\u8bfb\u3002\u54c8\u5e0c\u5e03\u5c40\u505a\u533a\u95f4\u53ea\u80fd\u6ee1\u76d8\u4e71\u8df3，\u968f\u673a IO \u6253\u6ee1\u3002\u4f60\u81ea\u7814\u5d4c\u5165\u5f0f\u5f15\u64ce\u3001\u53c8\u8dd1\u5728\u95ea\u5b58\u4e0a，\u8fd9\u4e00\u6761\u51e0\u4e4e\u5355\u72ec\u5c31\u80fd\u51b3\u5b9a\u4f60\u9009\u6709\u5e8f\u3002<\/p>\n<\/li>\n

  • \n

    \u7f13\u5b58\u7b56\u7565\u3002\u00a0\u6709\u5e8f\u7ed3\u6784\u7684\u6570\u636e\u5757\u5929\u7136\u5e26\u5c40\u90e8\u6027，\u7f13\u5b58\u4e00\u4e2a\u5757，\u5757\u91cc\u4e00\u6279\u76f8\u90bb key \u5168\u8ddf\u7740\u70ed\u4e86，\u8303\u56f4\u626b\u63cf\u7684\u7f13\u5b58\u547d\u4e2d\u7387\u5f88\u9ad8\u3002\u54c8\u5e0c\u8868\u7f13\u5b58\u4e00\u4e2a\u6876，\u6876\u91cc\u7684 key \u5728\u903b\u8f91\u4e0a\u6beb\u65e0\u5173\u8054，\u7f13\u5b58\u4ef7\u503c\u4f4e\u5f97\u591a\u3002<\/p>\n<\/li>\n

  • \n

    \u540e\u53f0\u6574\u7406\u3002\u00a0\u6709\u5e8f\u7ed3\u6784（\u5178\u578b\u5c31\u662f LSM）\u628a\u65b0\u5199\u5165\u6512\u5728\u5185\u5b58，\u6392\u597d\u5e8f\u5237\u6210\u4e00\u4e2a\u4e2a\u6709\u5e8f\u6587\u4ef6，\u518d\u9760\u540e\u53f0\u538b\u7f29\u628a\u591a\u4e2a\u6709\u5e8f\u6587\u4ef6\u5f52\u5e76\u6210\u66f4\u5927\u7684\u6709\u5e8f\u6587\u4ef6\u2014\u2014\u6574\u4e2a\u673a\u5236\u7684\u5730\u57fa\u5c31\u662f\u201c\u5f52\u5e76\u4e24\u4e2a\u6709\u5e8f\u5e8f\u5217\u5f88\u4fbf\u5b9c\u201d\u3002\u54c8\u5e0c\u5e03\u5c40\u6ca1\u6709\u8fd9\u4e2a\u4fbf\u5229\u3002<\/p>\n<\/li>\n<\/ul>\n

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    5. \u201c\u6301\u4e45\u5316\u3001\u6709\u7248\u672c\u7684\u6709\u5e8f Map\u201d\u8fd9\u4e5d\u4e2a\u5b57，\u9010\u4e2a\u5151\u73b0<\/h3>\n

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    C++<\/p>\n

    \/\/ db.h
    \n\/\/ A DB is a persistent, versioned ordered map from keys to values.
    \n\/\/ A DB is safe for concurrent access from multiple threads without
    \n\/\/ any external synchronization.
    \nclass DB {<\/p>\n

      \n
    • \n

      Map from keys to values\u2014\u2014\u7b2c 1 \u8282\u3002\u5c31\u662f\u4e2a key \u5230 value \u7684\u6620\u5c04，Put\/Get\/Delete，\u4f60\u8111\u5b50\u91cc\u90a3\u4e2a map \u5fc3\u667a\u662f\u5bf9\u7684\u3002<\/p>\n<\/li>\n

    • \n

      Ordered\u2014\u2014\u7b2c 3\u30014 \u8282\u3002\u8fd9\u4e2a map \u7684\u952e\u7a7a\u95f4\u4e0a\u6709\u4e00\u4e2a\u7531\u6bd4\u8f83\u5668\u5b9a\u4e49\u7684\u5168\u5e8f，\u4e8e\u662f\u5b83\u80fd\u8303\u56f4\u626b\u63cf，\u4e8e\u662f\u5b83\u7684\u78c1\u76d8\u548c\u7f13\u5b58\u5168\u4e3a\u987a\u5e8f\u8bbf\u95ee\u670d\u52a1\u3002\u8fd9\u662f\u5b83\u548c\u00a0std::unordered_map\u00a0\u7684\u5206\u6c34\u5cad\u3002<\/p>\n<\/li>\n

    • \n

      Persistent\u2014\u2014\u8de8\u8fdb\u7a0b\u6d3b\u7740，\u843d\u5728\u78c1\u76d8\u4e0a，\u8fdb\u7a0b\u91cd\u542f\u6570\u636e\u8fd8\u5728\u3002\u8fd9\u4e5f\u662f\u5b83\u5fc5\u987b\u5bf9\u4ed8\u78c1\u76d8 IO \u548c\u7f13\u5b58\u7684\u6839\u672c\u539f\u56e0：\u5185\u5b58\u91cc\u7684 map \u4e0d\u9700\u8981\u8003\u8651\u8fd9\u4e9b，\u4e00\u4e2a\u8981\u843d\u76d8\u7684 map \u5fc5\u987b\u8003\u8651\u3002<\/p>\n<\/li>\n

    • \n

      Versioned\u2014\u2014\u8fd9\u4e2a\u8bcd\u7b2c 1\u30012 \u8282\u57cb\u4e86\u4e24\u6b21\u4f0f\u7b14\u3002\u8fd8\u8bb0\u5f97\u5417，\u6211\u8bf4\u8fc7\u201c\u66f4\u65b0\u5176\u5b9e\u6ca1\u8986\u76d6\u4efb\u4f55\u4e1c\u897f\u201d\u201c\u5220\u9664\u7559\u4e0b\u5893\u7891\u201d\u3002\u771f\u76f8\u662f：\u8fd9\u4e2a map \u771f\u6b63\u5b58\u7684\u662f\u201ckey + \u7248\u672c\u53f7 \u2192 value\u201d\u3002\u6bcf\u4e00\u6b21\u00a0Put\u3001\u6bcf\u4e00\u6b21\u00a0Delete，\u90fd\u662f\u5f80\u8fd9\u4e2a key \u4e0a\u53e0\u4e00\u4e2a\u5e26\u66f4\u65b0\u7248\u672c\u53f7\u7684\u65b0\u8bb0\u5f55，\u65e7\u7248\u672c\u8fd8\u5728\u5e95\u4e0b\u538b\u7740\u3002<\/p>\n<\/li>\n<\/ul>\n

      \u6700\u540e\u90a3\u53e5\u201csafe for concurrent access … without any external synchronization\u201d\u4e5f\u522b\u653e\u8fc7：\u8fd9\u4e2a map \u81ea\u5e26\u5e76\u53d1\u5b89\u5168，\u591a\u7ebf\u7a0b\u76f4\u63a5\u8bfb\u5199\u4e0d\u7528\u4f60\u5728\u5916\u9762\u52a0\u9501\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u65f6，\u8fd9\u662f\u4e00\u4e2a\u6602\u8d35\u7684\u627f\u8bfa\u2014\u2014\u5b83\u610f\u5473\u7740\u5185\u90e8\u6240\u6709\u7684\u987a\u5e8f\u7ed3\u6784\u3001\u7f13\u5b58\u3001\u540e\u53f0\u6574\u7406\u90fd\u5f97\u81ea\u5df1\u625b\u4f4f\u5e76\u53d1，\u8fd9\u7b14\u590d\u6742\u5ea6\u662f\u7701\u4e0d\u6389\u7684\u3002\u8fd9\u6761\u627f\u8bfa\u8fd8\u53cd\u8fc7\u6765\u6536\u7d27\u4e86\u524d\u9762\u6bcf\u4e00\u5c42：\u6bd4\u8f83\u5668\u5fc5\u987b\u7ebf\u7a0b\u5b89\u5168（comparator.h \u660e\u8bf4\u5b83\u4f1a\u88ab\u591a\u4e2a\u8bfb\u7ebf\u7a0b\u540c\u65f6\u8c03\u7528），\u7f13\u5b58\u5f97\u7528\u5e76\u53d1\u5b89\u5168\u7684\u6dd8\u6c70\u7ed3\u6784，\u540e\u53f0\u538b\u7f29\u8981\u548c\u524d\u53f0\u8bfb\u5199\u62a2\u540c\u4e00\u6279\u6570\u636e\u8fd8\u4e0d\u8bb8\u4e92\u76f8\u8e29\u3002\u4f60\u80fd\u5728\u63a5\u53e3\u4e0a\u5199\u4e0b\u201c\u4e0d\u7528\u5916\u90e8\u52a0\u9501\u201d\u8fd9\u4e00\u53e5，\u80cc\u540e\u662f\u628a\u5e76\u53d1\u7684\u5168\u90e8\u590d\u6742\u5ea6\u54bd\u8fdb\u4e86\u5b9e\u73b0\u91cc\u3001\u4e00\u70b9\u6ca1\u6f0f\u7ed9\u8c03\u7528\u65b9\u3002<\/p>\n

      \u201c\u6709\u7248\u672c\u201d\u8fd9\u4e2a\u8bcd，\u662f\u7b2c\u4e00\u90e8\u5206\u901a\u5f80\u540e\u9762\u4e24\u90e8\u5206\u7684\u6697\u95e8\u3002\u5b83\u4e00\u5934\u8fde\u7740\u201c\u9519\u8bef\u4e0e\u63a5\u53e3\u5206\u5c42\u201d\u2014\u2014\u56e0\u4e3a\u591a\u7248\u672c\u3001\u5e76\u53d1\u3001\u540e\u53f0\u538b\u7f29\u8fd9\u4e9b\u590d\u6742\u5ea6，\u5fc5\u987b\u88ab\u4e00\u5c42\u7a33\u5b9a\u7684\u63a5\u53e3\u5305\u4f4f，\u4e0d\u80fd\u6f0f\u7ed9\u4f60；\u53e6\u4e00\u5934\u8fde\u7740\u201c\u5bf9\u8c61\u751f\u547d\u5468\u671f\u201d\u2014\u2014\u56e0\u4e3a\u6709\u4e86\u7248\u672c，\u624d\u4f1a\u6709\u201c\u8fd9\u6761\u65e7\u6570\u636e\u8fd8\u5b58\u5728，\u4f46\u4f60\u5df2\u7ecf\u770b\u4e0d\u89c1\u5b83\u4e86\u201d\u8fd9\u79cd\u8be1\u5f02\u72b6\u6001，\u624d\u4f1a\u6709\u5feb\u7167，\u624d\u4f1a\u6709\u5173\u5e93\u65f6\u90a3\u4e2a\u80fd\u628a\u4f60\u62e6\u4f4f\u7684\u672a\u91ca\u653e\u5f15\u7528\u3002\u63a5\u4e0b\u6765\u4e24\u90e8\u5206，\u5c31\u662f\u62c6\u8fd9\u4e24\u6247\u95e8\u3002<\/p>\n

      \n

      6. \u4e00\u4e2a\u7eaf\u865a\u57fa\u7c7b，\u4e00\u4e2a\u5de8\u578b\u5b9e\u73b0，\u63a5\u53e3\u548c\u5b9e\u73b0\u5c31\u8fd9\u4e48\u5206\u4e86\u5bb6<\/h3>\n

      \u7b2c\u4e00\u90e8\u5206\u4f60\u4e00\u76f4\u5728\u7528\u00a0DB\u00a0\u8fd9\u4e2a\u7c7b\u578b，Put\u3001Get\u3001NewIterator\u00a0\u90fd\u662f\u5b83\u7684\u65b9\u6cd5\u3002\u73b0\u5728\u628a\u5b83\u7684\u771f\u8eab\u7ffb\u51fa\u6765\u2014\u2014\u5b83\u662f\u4e2a\u7eaf\u865a\u57fa\u7c7b，\u4e00\u884c\u5b9e\u73b0\u90fd\u6ca1\u6709\u3002db.h \u7684\u7c7b\u6ce8\u91ca\u628a\u8fd9\u5c42\u5173\u7cfb\u4ea4\u4ee3\u5f97\u5f88\u5e72\u8106：<\/p>\n

      C++<\/p>\n

      \/\/ db.h
      \n\/\/ A DB is an abstract base class with one primary implementation
      \n\/\/ (DBImpl) and a number of wrapper implementations.
      \nclass DB {
      \n public:
      \n virtual Status Put(const WriteOptions&, ColumnFamilyHandle*,
      \n const Slice& key, const Slice& value) = 0;
      \n virtual Status Get(const ReadOptions&, ColumnFamilyHandle*,
      \n const Slice& key, PinnableSlice* value,
      \n std::string* timestamp) = 0;
      \n \/\/ … \u4e00\u6574\u5957 = 0 \u7684\u7eaf\u865a\u51fd\u6570
      \n};<\/p>\n

      = 0\u00a0\u7684\u7eaf\u865a\u51fd\u6570，\u4ece\u5934\u6392\u5230\u5c3e\u3002\u771f\u6b63\u5e72\u6d3b\u7684\u5b9e\u73b0\u5728\u53e6\u4e00\u4e2a\u76ee\u5f55\u3001\u53e6\u4e00\u4e2a\u7c7b\u91cc，db_impl.h：<\/p>\n

      C++<\/p>\n

      \/\/ db_impl.h
      \n\/\/ Since it's a very large class, the definition of the functions is
      \n\/\/ divided in several db_impl_*.cc files, besides db_impl.cc.
      \nclass DBImpl : public DB {
      \n public:
      \n \/\/ —- Implementations of the DB interface —-
      \n Status Put(const WriteOptions& options, ColumnFamilyHandle* column_family,
      \n const Slice& key, const Slice& value) override;
      \n Status Delete(const WriteOptions& options, ColumnFamilyHandle* column_family,
      \n const Slice& key) override;
      \n \/\/ … \u628a DB \u7684\u6bcf\u4e2a\u7eaf\u865a\u51fd\u6570 override \u4e00\u904d
      \n};<\/p>\n

      \u6ce8\u91ca\u8bf4\u5f97\u5f88\u5b9e\u5728\u2014\u2014\u201c\u56e0\u4e3a\u8fd9\u4e2a\u7c7b\u5b9e\u5728\u592a\u5927，\u5b83\u7684\u51fd\u6570\u5b9a\u4e49\u88ab\u62c6\u5230\u597d\u51e0\u4e2a db_impl_*.cc \u6587\u4ef6\u91cc\u201d\u3002\u8fd9\u5c31\u662f\u63a5\u53e3\u548c\u5b9e\u73b0\u5206\u5bb6\u7684\u610f\u4e49：DB\u00a0\u662f\u4e00\u5f20\u8584\u8584\u7684\u5951\u7ea6，\u51e0\u767e\u884c\u7eaf\u865a\u58f0\u660e；DBImpl\u00a0\u662f\u90a3\u53f0\u771f\u6b63\u5904\u7406\u5185\u5b58\u8868\u3001\u9884\u5199\u65e5\u5fd7\u3001\u540e\u53f0\u538b\u7f29\u3001\u5e76\u53d1\u63a7\u5236\u7684\u5e9e\u7136\u5927\u7269，\u6563\u5728\u5341\u51e0\u4e2a\u6e90\u6587\u4ef6\u91cc\u3002\u4f60\u56de\u5934\u770b\u7b2c 1 \u8282\u7684\u00a0DB::Open：<\/p>\n

      C++<\/p>\n

      \/\/ db.h
      \nstatic Status Open(const Options& options, const std::string& name,
      \n std::unique_ptr<DB>* dbptr);<\/p>\n

      \u5b83\u4ea4\u8fd8\u7ed9\u4f60\u7684\u662f\u00a0unique_ptr<DB>\u2014\u2014\u63a5\u53e3\u7c7b\u578b\u7684\u667a\u80fd\u6307\u9488\u3002\u4f60\u4ece\u5934\u5230\u5c3e\u6478\u5230\u7684\u90fd\u662f\u90a3\u5f20\u8584\u5951\u7ea6\u00a0DB，DBImpl\u00a0\u8fd9\u4e2a\u540d\u5b57\u4f60\u5728\u81ea\u5df1\u4ee3\u7801\u91cc\u6839\u672c\u4e0d\u9700\u8981\u51fa\u73b0\u3002\u8fd9\u5c31\u662f\u201c\u7a33\u5b9a\u516c\u5171 API\u201d\u548c\u201c\u5185\u90e8\u5b9e\u73b0\u201d\u7684\u7269\u7406\u8fb9\u754c：\u5e95\u4e0b\u90a3\u53f0\u5e9e\u7136\u5927\u7269\u968f\u7248\u672c\u600e\u4e48\u91cd\u6784\u3001\u62c6\u51e0\u4e2a\u6587\u4ef6\u3001\u6362\u4ec0\u4e48\u6570\u636e\u7ed3\u6784，\u53ea\u8981\u00a0DB\u00a0\u8fd9\u5f20\u7eaf\u865a\u5951\u7ea6\u4e0d\u53d8，\u4f60\u7684\u4ee3\u7801\u4e00\u884c\u90fd\u4e0d\u7528\u6539\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u65f6\u5982\u679c\u53ea\u5b66\u4e00\u6761 API \u8bbe\u8ba1\u539f\u5219，\u5c31\u5b66\u8fd9\u6761\u2014\u2014\u5bf9\u5916\u4ea4\u51fa\u4e00\u4e2a\u7eaf\u865a\u63a5\u53e3\u548c\u4e00\u4e2a\u5de5\u5382\u51fd\u6570（\u8fd9\u91cc\u662f\u00a0Open），\u628a\u5b9e\u73b0\u7c7b\u5f7b\u5e95\u710a\u6b7b\u5728\u4f60\u7684 .cc \u6587\u4ef6\u91cc，\u6c38\u8fdc\u4e0d\u8fdb\u516c\u5171\u5934\u3002<\/p>\n

      \u8fd9\u5c42\u5206\u5bb6\u8fd8\u987a\u624b\u4e70\u5230\u4e00\u6837\u4f60\u73b0\u5728\u53ef\u80fd\u6ca1\u5728\u610f\u3001\u53d1\u5e03\u5e93\u65f6\u5374\u4f1a\u6551\u547d\u7684\u4e1c\u897f\u2014\u2014ABI \u7a33\u5b9a\u3002DB\u00a0\u662f\u7eaf\u865a\u57fa\u7c7b，\u4f60\u7684\u4ee3\u7801\u901a\u8fc7\u5b83\u7684\u865a\u8868\u8c03\u00a0Put\/Get，\u7f16\u8bd1\u671f\u4f60\u53ea\u4f9d\u8d56\u201c\u8fd9\u4e2a\u65b9\u6cd5\u6392\u5728\u865a\u8868\u7b2c\u51e0\u4e2a\u201d\u8fd9\u4e2a\u504f\u79fb，\u4e0d\u4f9d\u8d56\u00a0DBImpl\u00a0\u91cc\u6709\u54ea\u4e9b\u6210\u5458\u3001\u600e\u4e48\u6392\u5e03\u3002\u4e8e\u662f\u5e95\u5c42\u5b9e\u73b0\u52a0\u4e2a\u5b57\u6bb5\u3001\u6362\u4e2a\u6570\u636e\u7ed3\u6784\u3001\u91cd\u6392\u79c1\u6709\u6210\u5458，\u4f60\u7684\u4e8c\u8fdb\u5236\u4e00\u884c\u90fd\u4e0d\u7528\u91cd\u7f16，\u53ea\u8981\u865a\u8868\u7684\u5f62\u72b6\u4e0d\u53d8\u3002\u8fd9\u6b63\u662f\u4ee5\u00a0.so\u00a0\/\u00a0.dll\u00a0\u53d1\u5e03\u7684\u5e93\u68a6\u5bd0\u4ee5\u6c42\u7684\u6027\u8d28：\u63a5\u53e3\u4e0e\u5b9e\u73b0\u5728\u4e8c\u8fdb\u5236\u5c42\u9762\u89e3\u8026\u3002\u4ee3\u4ef7\u662f\u6bcf\u6b21\u8c03\u7528\u591a\u4e00\u8df3\u865a\u8868\u95f4\u63a5\u5bfb\u5740，\u4f46\u5bf9\u4e00\u4e2a\u52a8\u8f84\u8981\u8bfb\u76d8\u7684\u64cd\u4f5c，\u8fd9\u4e00\u8df3\u7684\u5f00\u9500\u5c0f\u5230\u53ef\u4ee5\u5ffd\u7565\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u82e5\u8981\u7ed9\u4e0b\u6e38\u53d1\u4e8c\u8fdb\u5236，\u201c\u7eaf\u865a\u63a5\u53e3 + \u5de5\u5382\u51fd\u6570\u201d\u51e0\u4e4e\u662f\u552f\u4e00\u625b\u5f97\u4f4f\u7248\u672c\u6f14\u8fdb\u7684\u5f62\u72b6\u2014\u2014\u628a\u5b9e\u73b0\u585e\u8fdb\u516c\u5171\u5934\u7684\u90a3\u4e00\u523b，\u4f60\u5c31\u628a\u81ea\u5df1\u710a\u6b7b\u5728\u4e86\u4e00\u4e2a\u518d\u4e5f\u6539\u4e0d\u52a8\u7684\u5185\u5b58\u5e03\u5c40\u4e0a\u3002<\/p>\n

      \u5206\u5c42\u8fd8\u6709\u66f4\u7ec6\u7684\u4e00\u624b\u3002\u770b\u00a0Get\u00a0\u8fd9\u4e00\u65cf\u5728 db.h \u91cc\u7684\u6837\u5b50，\u5b83\u4e0d\u6b62\u4e00\u4e2a：<\/p>\n

      C++<\/p>\n

      \/\/ db.h：\u771f\u6b63\u8981\u88ab\u5b9e\u73b0\u7684，\u53ea\u6709\u8fd9\u4e00\u4e2a\u7eaf\u865a\u7248\u672c
      \nvirtual Status Get(const ReadOptions&, ColumnFamilyHandle*, const Slice& key,
      \n PinnableSlice* value, std::string* timestamp) = 0;<\/p>\n

      \/\/ \u5176\u4f59\u5168\u662f final \u7684\u4fbf\u5229\u91cd\u8f7d，\u6536\u655b\u5230\u4e0a\u9762\u90a3\u4e2a
      \n\/\/ NOTE: virtual final => disallow override (was previously allowed)
      \nvirtual Status Get(const ReadOptions& options, const Slice& key,
      \n std::string* value) final {
      \n return Get(options, DefaultColumnFamily(), key, value);
      \n}<\/p>\n

      \u4e00\u4e2a\u00a0Get\u00a0\u5bb6\u65cf，\u53ea\u6709\u90a3\u4e2a\u5e26\u00a0PinnableSlice*\u00a0\u548c\u00a0timestamp*\u00a0\u7684\u7248\u672c\u662f\u7eaf\u865a\u7684\u2014\u2014\u5b83\u662f\u552f\u4e00\u7684\u5b9e\u73b0\u70b9\u3002\u5176\u4f59\u4f60\u5929\u5929\u7528\u7684\u90a3\u4e9b\u201c\u7701\u4e8b\u7248\u201d（\u7701\u6389\u5217\u65cf\u53c2\u6570\u3001value \u76f4\u63a5\u7ed9\u00a0std::string）\u5168\u662f\u00a0final，\u8c01\u90fd\u4e0d\u8bb8\u518d override，\u5b83\u4eec\u53ea\u505a\u4e00\u4ef6\u4e8b：\u8865\u4e0a\u9ed8\u8ba4\u53c2\u6570，\u628a\u8c03\u7528\u8f6c\u53d1\u8fdb\u90a3\u4e2a\u552f\u4e00\u7684\u7eaf\u865a\u00a0Get\u3002\u6ce8\u91ca\u91cc\u90a3\u53e5\u00a0disallow override (was previously allowed)\u00a0\u662f\u6709\u6545\u4e8b\u7684\u2014\u2014\u65e9\u5e74\u8fd9\u4e9b\u91cd\u8f7d\u4e0d\u662f\u00a0final，\u4e8e\u662f\u6bcf\u4e2a\u60f3\u5b9a\u5236\u7684\u5b50\u7c7b\u90fd\u5f97\u628a\u4e03\u516b\u4e2a\u91cd\u8f7d\u5404\u5b9e\u73b0\u4e00\u904d，\u7a0d\u4e0d\u7559\u795e\u5c31\u6f0f\u6389\u4e00\u4e2a\u3001\u884c\u4e3a\u4e0d\u4e00\u81f4\u3002\u6539\u6210\u00a0final\u00a0\u4e4b\u540e，\u5b9e\u73b0\u8005\u7684\u4e49\u52a1\u88ab\u6536\u7a84\u5230\u4e00\u4e2a\u65b9\u6cd5，\u4fbf\u5229\u6027\u7559\u7ed9\u8c03\u7528\u65b9，\u4e00\u81f4\u6027\u7531\u7f16\u8bd1\u671f\u4fdd\u8bc1\u3002<\/p>\n

      \u5230\u00a0DBImpl\u00a0\u91cc，\u8fd9\u4e2a\u552f\u4e00\u7684\u7eaf\u865a\u00a0Get\u00a0\u53c8\u8f6c\u53d1\u8fdb\u4e00\u4e2a\u66f4\u5185\u90e8\u7684\u5b9e\u73b0\u51fd\u6570：<\/p>\n

      C++<\/p>\n

      \/\/ db_impl.h：DBImpl \u91cc，\u516c\u5f00\u7684 Get \u4e4b\u4e0b\u8fd8\u6709\u4e00\u5c42\u5185\u90e8\u7684 GetImpl
      \nStatus GetMergeOperands(const ReadOptions& options,
      \n ColumnFamilyHandle* column_family, const Slice& key,
      \n PinnableSlice* merge_operands, \/* … *\/) override {
      \n GetImplOptions get_impl_options;
      \n get_impl_options.column_family = column_family;
      \n get_impl_options.merge_operands = merge_operands;
      \n get_impl_options.get_value = false;
      \n return GetImpl(options, key, get_impl_options);
      \n}<\/p>\n

      \u4e8e\u662f\u8bfb\u8def\u5f84\u662f\u4e09\u5c42\u5957\u5a03：\u6700\u5916\u5c42\u662f\u4e00\u5806\u00a0final\u00a0\u4fbf\u5229\u91cd\u8f7d（\u516c\u5171 API \u7684\u4eba\u4f53\u5de5\u5b66），\u4e2d\u95f4\u662f\u552f\u4e00\u7684\u865a\u51fd\u6570\u00a0Get（\u591a\u6001\u7684\u5b9e\u73b0\u70b9\u3001\u4e5f\u662f\u7a33\u5b9a\u7684 ABI \u8fb9\u754c），\u6700\u91cc\u5c42\u662f\u00a0GetImpl\u00a0\u5e26\u4e00\u4e2a\u00a0GetImplOptions\u00a0\u53c2\u6570\u5305（\u5185\u90e8\u5b9e\u73b0，\u968f\u4fbf\u600e\u4e48\u6539）\u3002\u00a0\u70b9\u67e5\u3001\u8bfb\u5408\u5e76\u7b97\u5b50\u3001\u591a\u952e\u6279\u91cf\u8bfb，\u6700\u540e\u90fd\u6c47\u5230\u00a0GetImpl\u00a0\u8fd9\u4e00\u4e2a\u6d1e\u91cc\u3002\u8fd9\u4e2a\u7ed3\u6784\u503c\u5f97\u4f60\u6284\u8fdb\u81ea\u7814\u5f15\u64ce：\u628a\u201c\u7ed9\u8c03\u7528\u65b9\u7684\u82b1\u6837\u201d\u548c\u201c\u7ed9\u5b9e\u73b0\u8005\u7684\u4e49\u52a1\u201d\u5206\u5f00，\u524d\u8005\u5c3d\u7ba1\u591a，\u540e\u8005\u6536\u655b\u5230\u4e00\u4e2a\u5185\u90e8\u51fd\u6570\u4e0a，\u4e2d\u95f4\u7528\u4e00\u4e2a\u7a33\u5b9a\u7684\u865a\u63a5\u53e3\u9694\u5f00\u3002<\/p>\n

      7. \u9519\u8bef\u662f\u503c\u4e0d\u662f\u5f02\u5e38：Status \u4e0e\u90a3\u4e2a\u4f1a abort \u7684\u6790\u6784\u51fd\u6570<\/h3>\n

      \u7b2c 1\u30012 \u8282\u6211\u4e24\u6b21\u5356\u8fc7\u5173\u5b50，\u8bf4\u8fd9\u53f0\u5f15\u64ce\u4e0d\u7528\u5f02\u5e38\u3002\u73b0\u5728\u5151\u73b0\u3002\u5b83\u7684\u6574\u4e2a\u9519\u8bef\u901a\u9053\u5c31\u662f\u90a3\u4e2a\u5230\u5904\u51fa\u73b0\u7684\u8fd4\u56de\u503c\u00a0Status\u3002\u5148\u770b\u5b83\u627f\u8f7d\u4ec0\u4e48，status.h：<\/p>\n

      C++<\/p>\n

      \/\/ status.h
      \nenum Code : unsigned char {
      \n kOk = 0,
      \n kNotFound = 1,
      \n kCorruption = 2,
      \n kNotSupported = 3,
      \n kInvalidArgument = 4,
      \n kIOError = 5,
      \n \/\/ … \u4e00\u76f4\u5230
      \n kColumnFamilyDropped = 15,
      \n};<\/p>\n

      \u4e00\u4e2a\u5b57\u8282\u7684\u9519\u8bef\u7801，\u5341\u516d\u79cd\u3002kNotFound\u00a0\u53ea\u662f\u5176\u4e2d\u666e\u666e\u901a\u901a\u7684\u4e00\u53f7\u2014\u2014\u67e5\u4e0d\u5230\u3001IO \u9519\u3001\u6570\u636e\u635f\u574f\u3001\u53c2\u6570\u975e\u6cd5\u3001\u5217\u65cf\u88ab\u5220，\u5168\u90fd\u662f\u540c\u4e00\u4e2a\u00a0Status\u00a0\u503c\u7684\u4e0d\u540c\u53d6\u503c，\u987a\u7740\u51fd\u6570\u8fd4\u56de\u503c\u4e00\u5c42\u5c42\u5f80\u4e0a\u4f20\u3002\u6ca1\u6709\u00a0throw，\u6ca1\u6709\u00a0catch，\u6ca1\u6709\u6808\u5c55\u5f00\u3002<\/p>\n

      \u4e3a\u4ec0\u4e48\u4e00\u53f0\u8fd9\u4e48\u590d\u6742\u7684\u5f15\u64ce，\u5b81\u53ef\u7528\u8fd4\u56de\u503c\u4e5f\u4e0d\u7528\u5f02\u5e38？\u6bd4\u8f83\u5668\u90a3\u4e2a\u5934\u6587\u4ef6\u91cc\u6709\u4e00\u53e5\u6700\u76f4\u767d\u7684\u89e3\u91ca：<\/p>\n

      C++<\/p>\n

      \/\/ comparator.h
      \n\/\/ Exceptions MUST NOT propagate out of overridden functions into
      \n\/\/ RocksDB, because RocksDB is not exception-safe. This could cause
      \n\/\/ undefined behavior including data loss, unreported corruption,
      \n\/\/ deadlocks, and more.<\/p>\n

      \u201c\u8fd9\u53f0\u5f15\u64ce\u4e0d\u662f\u5f02\u5e38\u5b89\u5168\u7684\u3002\u201d\u00a0\u4e00\u4e2a\u6301\u6709\u5185\u90e8\u9501\u3001\u7ba1\u7740\u4e00\u5806\u591a\u7248\u672c\u6570\u636e\u3001\u540e\u53f0\u8fd8\u6709\u538b\u7f29\u7ebf\u7a0b\u5728\u8dd1\u7684\u7cfb\u7edf，\u5982\u679c\u8ba9\u5f02\u5e38\u5728\u4efb\u610f\u4e00\u5c42\u968f\u610f\u7a7f\u8fc7\u53bb，\u6808\u5c55\u5f00\u4f1a\u7ed5\u8fc7\u5b83\u7cbe\u5fc3\u5b89\u6392\u7684\u89e3\u9501\u3001\u56de\u6eda\u3001\u72b6\u6001\u590d\u4f4d，\u8f7b\u5219\u6b7b\u9501，\u91cd\u5219\u4e22\u6570\u636e\u3001\u635f\u574f\u8fd8\u4e0d\u4e0a\u62a5\u3002\u6240\u4ee5\u5b83\u7684\u9009\u62e9\u662f：\u5728\u6240\u6709\u6743\u548c\u8d44\u6e90\u8fb9\u754c\u4e0a\u4e0d\u4fe1\u4efb\u5f02\u5e38，\u628a\u9519\u8bef\u538b\u5e73\u6210\u4e00\u4e2a\u5fc5\u987b\u88ab\u9010\u5c42\u68c0\u67e5\u3001\u9010\u5c42\u4f20\u9012\u7684\u503c\u3002\u00a0\u4f60\u81ea\u7814\u5f15\u64ce\u3001\u5c24\u5176\u6d89\u53ca\u78c1\u76d8\u548c\u5e76\u53d1\u65f6，\u8fd9\u662f\u4e00\u4e2a\u503c\u5f97\u8ba4\u771f\u6382\u91cf\u7684\u7acb\u573a\u2014\u2014\u5f02\u5e38\u5728\u4e1a\u52a1\u4ee3\u7801\u91cc\u5f88\u9999，\u4f46\u5728\u4e00\u4e2a\u4e0d\u80fd\u5bb9\u5fcd\u201c\u534a\u4e2a\u64cd\u4f5c\u201d\u7684\u5b58\u50a8\u5f15\u64ce\u6838\u5fc3\u91cc，\u8fd4\u56de\u503c\u9519\u8bef\u7801\u7684\u53ef\u9884\u6d4b\u6027\u5f80\u5f80\u66f4\u503c\u94b1\u3002<\/p>\n

      \u4f46\u8fd4\u56de\u503c\u6709\u4e2a\u81f4\u547d\u5f31\u70b9：\u6ca1\u4eba\u5f3a\u8feb\u4f60\u68c0\u67e5\u3002\u00a0throw\u00a0\u51fa\u6765\u7684\u5f02\u5e38\u4f60\u4e0d\u63a5\u5c31\u5d29，\u8fd4\u56de\u7684\u00a0Status\u00a0\u4f60\u4e0d\u770b\u5c31\u6084\u6084\u6e9c\u8fc7\u53bb\u4e86\u3002\u8fd9\u53f0\u5f15\u64ce\u600e\u4e48\u5835\u8fd9\u4e2a\u6d1e？\u6211\u4eec\u8ba9\u5b83\u5f53\u573a\u5d29\u7ed9\u4f60\u770b\u3002\u5199\u4e00\u6bb5\u201c\u5fd8\u4e86\u68c0\u67e5\u8fd4\u56de\u503c\u201d\u7684\u4ee3\u7801，\u7528\u6253\u5f00\u4e86\u72b6\u6001\u68c0\u67e5\u7684\u7f16\u8bd1\u914d\u7f6e\u8dd1：<\/p>\n

      C++<\/p>\n

      \/\/ \u707e\u96be\u6f14\u793a：\u62ff\u5230 Status \u5374\u4e0d\u770b\u5b83
      \ndb->Put(WriteOptions(), "k", "v"); \/\/ \u8fd4\u56de\u7684 Status \u76f4\u63a5\u88ab\u4e22\u5f03
      \n\/\/ \u7a0b\u5e8f\u7ee7\u7eed\u5f80\u4e0b\u2026\u2026<\/p>\n

      \u5728\u5f00\u4e86\u00a0ASSERT_STATUS_CHECKED\u00a0\u7684\u6784\u5efa\u91cc，\u8fd9\u6bb5\u8dd1\u5230\u90a3\u4e2a\u88ab\u4e22\u5f03\u7684\u00a0Status\u00a0\u6790\u6784\u65f6，\u76f4\u63a5 abort：<\/p>\n

      text<\/p>\n

      Failed to check Status 0x7ffe1a3c9080
      \n #4 Status::~Status()
      \n #5 main
      \nAborted (core dumped)<\/p>\n

      \u79d8\u5bc6\u5168\u5728\u00a0Status\u00a0\u7684\u6790\u6784\u51fd\u6570\u91cc，status.h：<\/p>\n

      C++<\/p>\n

      \/\/ status.h
      \n~Status() {
      \n#ifdef ROCKSDB_ASSERT_STATUS_CHECKED
      \n if (!checked_) {
      \n fprintf(stderr, "Failed to check Status %p\\\\n", this);
      \n port::PrintStack();
      \n std::abort();
      \n }
      \n#endif
      \n}<\/p>\n

      \u6bcf\u4e2a\u00a0Status\u00a0\u5185\u90e8\u85cf\u4e86\u4e00\u4e2a\u00a0checked_\u00a0\u6807\u5fd7\u3002\u4f60\u8c03\u00a0ok()\u3001code()\u3001IsNotFound()\u00a0\u8fd9\u4e9b，\u90fd\u4f1a\u628a\u5b83\u6807\u8bb0\u4e3a\u201c\u5df2\u68c0\u67e5\u201d\u3002\u8981\u662f\u4e00\u4e2a\u00a0Status\u00a0\u5bf9\u8c61\u4e00\u8def\u6d3b\u5230\u6790\u6784\u90fd\u6ca1\u88ab\u4eba\u78b0\u8fc7\u4e00\u6b21，\u6790\u6784\u51fd\u6570\u5c31\u6253\u5370\u5730\u5740\u3001\u6253\u5370\u8c03\u7528\u6808\u3001std::abort()\u2014\u2014\u628a\u8fdb\u7a0b\u5f53\u573a\u5e72\u6389，\u903c\u4f60\u5728\u6d4b\u8bd5\u9636\u6bb5\u5c31\u628a\u8fd9\u4e2a\u6f0f\u68c0\u7684\u5730\u65b9\u63ea\u51fa\u6765\u3002\u8fd9\u5957\u68c0\u67e5\u53ea\u5728\u5e26\u00a0ASSERT_STATUS_CHECKED\u00a0\u7684\u8c03\u8bd5 \/ CI \u6784\u5efa\u91cc\u751f\u6548，\u53d1\u5e03\u7248\u662f\u96f6\u5f00\u9500\u7684（\u90a3\u6bb5\u4ee3\u7801\u6839\u672c\u4e0d\u7f16\u8fdb\u53bb）\u3002<\/p>\n

      \u90a3\u8981\u662f\u6211\u786e\u5b9e\u60f3\u4e22\u5f03\u4e00\u4e2a\u9519\u8bef\u5462？\u4e5f\u6709\u6b63\u89c4\u51fa\u53e3：<\/p>\n

      C++<\/p>\n

      \/\/ status.h
      \n\/\/ In case of intentionally swallowing an error, user must explicitly
      \n\/\/ call this function.
      \ninline void PermitUncheckedError() const { MarkChecked(); }<\/p>\n

      \u4f60\u5f97\u663e\u5f0f\u5199\u4e00\u53e5\u00a0s.PermitUncheckedError()，\u767d\u7eb8\u9ed1\u5b57\u58f0\u660e\u201c\u8fd9\u4e2a\u9519\u8bef\u6211\u662f\u6545\u610f\u4e0d\u5904\u7406\u7684\u201d\u3002\u8fd9\u53e5\u8bdd\u7684\u4ef7\u503c\u5168\u5728\u4ee3\u7801\u5ba1\u67e5\u2014\u2014\u5b83\u628a\u201c\u6211\u6f0f\u4e86\u201d\u548c\u201c\u6211\u6545\u610f\u7684\u201d\u4ece\u89c6\u89c9\u4e0a\u5f7b\u5e95\u5206\u5f00，\u5168\u5e93\u641c\u4e00\u4e0b\u5c31\u77e5\u9053\u54ea\u4e9b\u9519\u8bef\u662f\u88ab\u4eba\u6709\u610f\u54bd\u4e0b\u53bb\u7684\u3002\u8fd9\u662f\u628a\u4e00\u4e2a\u7eaf\u7ea6\u5b9a（\u8bf7\u8bb0\u5f97\u68c0\u67e5\u8fd4\u56de\u503c）\u5347\u7ea7\u6210\u4e86\u7f16\u8bd1\u671f\u53ef\u5f3a\u5236\u3001\u4ee3\u7801\u91cc\u53ef\u641c\u7d22\u7684\u7eaa\u5f8b\u3002\u00a0\u4f60\u81ea\u7814\u5f15\u64ce\u65f6\u5982\u679c\u4e5f\u8d70\u8fd4\u56de\u503c\u9519\u8bef\u901a\u9053，\u5f3a\u70c8\u5efa\u8bae\u6284\u8fd9\u4e00\u5957：\u5149\u6709\u00a0Status\u00a0\u4e0d\u591f，\u5f97\u6709\u4e00\u4e2a\u80fd\u5728\u6d4b\u8bd5\u91cc\u628a\u201c\u6f0f\u68c0\u201d\u53d8\u6210\u5d29\u6e83\u7684\u673a\u5236，\u5426\u5219\u8fd4\u56de\u503c\u9519\u8bef\u7801\u8fdf\u65e9\u4f1a\u88ab\u4eba\u8fd9\u91cc\u6f0f\u4e00\u4e2a\u90a3\u91cc\u6f0f\u4e00\u4e2a，\u9000\u5316\u6210\u6bd4\u5f02\u5e38\u8fd8\u5371\u9669\u7684\u4e1c\u897f\u2014\u2014\u56e0\u4e3a\u5f02\u5e38\u81f3\u5c11\u4e0d\u4f1a\u88ab\u65e0\u58f0\u541e\u6389\u3002<\/p>\n

      8. \u529f\u80fd\u600e\u4e48\u4e00\u5c42\u5c42\u53e0\u4e0a\u53bb，\u9760\u7684\u662f\u88c5\u9970<\/h3>\n

      \u5230\u8fd9\u91cc\u4f60\u624b\u91cc\u6709\u4e86\u4e24\u5757：\u4e00\u5f20\u7eaf\u865a\u5951\u7ea6\u00a0DB，\u4e00\u4e2a\u5de8\u578b\u5b9e\u73b0\u00a0DBImpl\u3002\u73b0\u5728\u6765\u4e2a\u771f\u95ee\u9898：\u6211\u60f3\u7ed9\u8fd9\u53f0\u5f15\u64ce\u52a0\u4e2a\u529f\u80fd，\u6bd4\u5982\u7ed9\u6240\u6709 key \u81ea\u52a8\u5e26 TTL \u8fc7\u671f，\u6216\u8005\u5199\u4e4b\u524d\u5148\u52a0\u5bc6\u3002\u5f80\u54ea\u52a0？<\/p>\n

      \u65b0\u624b\u7684\u7b2c\u4e00\u53cd\u5e94\u662f\u6539\u00a0DBImpl\u3002\u9519\u3002DBImpl\u00a0\u662f\u90a3\u53f0\u8c01\u90fd\u4e0d\u8be5\u78b0\u7684\u5e9e\u7136\u5927\u7269，\u4f60\u5f80\u91cc\u585e TTL \u903b\u8f91，\u7b49\u4e8e\u628a\u4e00\u4e2a\u6b63\u4ea4\u7684\u5173\u6ce8\u70b9\u710a\u6b7b\u8fdb\u6838\u5fc3\u5b9e\u73b0\u3002\u6b63\u786e\u7b54\u6848\u662f\u88c5\u9970，\u5b83\u7ed9\u4f60\u73b0\u6210\u7684\u57fa\u7c7b，stackable_db.h：<\/p>\n

      C++<\/p>\n

      \/\/ stackable_db.h
      \n\/\/ This class contains APIs to stack rocksdb wrappers.
      \n\/\/ Eg. Stack TTL over base db.
      \nclass StackableDB : public DB {
      \n public:
      \n explicit StackableDB(DB* db) : db_(db) {} \/\/ \u72ec\u5360\u5e95\u5c42 db<\/p>\n

      Status Put(const WriteOptions& options, ColumnFamilyHandle* cf,
      \n const Slice& key, const Slice& val) override {
      \n return db_->Put(options, cf, key, val); \/\/ \u539f\u6837\u8f6c\u53d1
      \n }
      \n Status DropColumnFamily(ColumnFamilyHandle* cf) override {
      \n return db_->DropColumnFamily(cf); \/\/ \u539f\u6837\u8f6c\u53d1
      \n }
      \n virtual DB* GetBaseDB() { return db_; } \/\/ \u9732\u51fa\u88ab\u5305\u7684\u90a3\u5c42
      \n DB* GetRootDB() override { return db_->GetRootDB(); } \/\/ \u9012\u5f52\u5230\u6700\u5e95
      \n private:
      \n DB* db_;
      \n};<\/p>\n

      StackableDB\u00a0\u81ea\u5df1\u5c31\u662f\u4e00\u4e2a\u00a0DB（public DB），\u5b83\u6301\u6709\u53e6\u4e00\u4e2a\u00a0DB，\u628a\u6bcf\u4e00\u4e2a\u65b9\u6cd5\u539f\u5c01\u4e0d\u52a8\u8f6c\u53d1\u7ed9\u91cc\u9762\u90a3\u4e2a\u3002\u5b83\u81ea\u5df1\u4ec0\u4e48\u6d3b\u90fd\u4e0d\u5e72\u2014\u2014\u5b83\u7684\u4ef7\u503c\u6070\u6070\u5728\u4e8e\u201c\u4ec0\u4e48\u90fd\u4e0d\u5e72\u201d，\u56e0\u4e3a\u8fd9\u6837\u4f60\u5c31\u6709\u4e86\u4e00\u4e2a\u5e72\u51c0\u7684\u63d2\u5165\u70b9：\u7ee7\u627f\u00a0StackableDB，\u53ea\u91cd\u5199\u4f60\u5173\u5fc3\u7684\u90a3\u51e0\u4e2a\u65b9\u6cd5\u3002TTL \u5c31\u91cd\u5199\u00a0Put，\u585e\u4e00\u4e2a\u8fc7\u671f\u65f6\u95f4\u6233\u518d\u8f6c\u53d1；\u52a0\u5bc6\u5c31\u91cd\u5199\u00a0Put\/Get，\u8fdb\u51fa\u5404\u505a\u4e00\u6b21\u5bc6\u7801\u5b66\u53d8\u6362；\u7edf\u8ba1\u5c31\u6bcf\u4e2a\u65b9\u6cd5\u8f6c\u53d1\u524d\u540e\u8bb0\u4e00\u7b14\u8017\u65f6\u3002\u5176\u4f59\u51e0\u5341\u4e2a\u65b9\u6cd5，\u57fa\u7c7b\u66ff\u4f60\u539f\u6837\u900f\u4f20，\u4f60\u4e00\u884c\u90fd\u4e0d\u7528\u78b0\u3002\u8fd9\u5c31\u662f\u88c5\u9970\u5668：\u529f\u80fd\u50cf\u5957\u58f3\u4e00\u6837\u4e00\u5c42\u5c42\u53e0\u4e0a\u53bb，\u6bcf\u4e00\u5c42\u53ea\u8ba4\u5b83\u4e0b\u9762\u662f\u4e2a\u00a0DB，\u4e0d\u8ba4\u5177\u4f53\u662f\u8c01\u3002\u00a0TTL \u58f3\u53ef\u4ee5\u5957\u5728\u52a0\u5bc6\u58f3\u4e0a，\u52a0\u5bc6\u58f3\u5957\u5728\u00a0DBImpl\u00a0\u4e0a，GetRootDB()\u00a0\u4e00\u8def\u00a0db_->\u00a0\u9012\u5f52\u5230\u6700\u5e95\u90a3\u4e2a\u771f\u8eab\u3002<\/p>\n

      \u987a\u4fbf\u628a\u5b83\u7684\u6240\u6709\u6743\u4e5f\u70b9\u7834，\u56e0\u4e3a\u8fd9\u662f\u81ea\u7814\u5f15\u64ce\u6700\u5bb9\u6613\u57cb\u96f7\u7684\u5730\u65b9\u3002StackableDB\u00a0\u7ed9\u4e86\u4e09\u4e2a\u6784\u9020\u51fd\u6570，\u5bf9\u5e94\u4e09\u79cd\u6240\u6709\u6743：<\/p>\n

      C++<\/p>\n

      \/\/ stackable_db.h
      \nexplicit StackableDB(DB* db) : db_(db) {} \/\/ \u88f8\u6307\u9488，\u72ec\u5360
      \nexplicit StackableDB(std::shared_ptr<DB> db) \/\/ \u5171\u4eab
      \n : db_(db.get()), shared_db_ptr_(db) {}
      \nexplicit StackableDB(std::unique_ptr<DB>&& db) \/\/ \u79fb\u4ea4\u72ec\u5360
      \n : db_(db.get()), shared_db_ptr_(std::move(db)) {}
      \n~StackableDB() override {
      \n if (shared_db_ptr_ == nullptr) {
      \n delete db_; \/\/ \u72ec\u5360\u6a21\u5f0f：\u6211\u6790\u6784，\u6211\u8d1f\u8d23\u5220\u5e95\u5c42
      \n } else {
      \n assert(shared_db_ptr_.get() == db_); \/\/ \u5171\u4eab\u6a21\u5f0f：\u4ea4\u7ed9 shared_ptr
      \n }
      \n}<\/p>\n

      \u5b83\u628a\u201c\u6211\u5230\u5e95\u62e5\u4e0d\u62e5\u6709\u88ab\u5305\u7684\u90a3\u4e2a\u00a0DB\u201d\u8fd9\u4ef6\u4e8b，\u5728\u6784\u9020\u51fd\u6570\u7b7e\u540d\u91cc\u5c31\u644a\u5f00\u8bf4\u6e05\u695a\u4e86\u2014\u2014\u4f20\u88f8\u6307\u9488\u6216\u00a0unique_ptr\u00a0\u5c31\u662f\u201c\u8fd9\u4e2a db \u5f52\u6211\u4e86，\u6211\u6790\u6784\u65f6\u5220\u5b83\u201d，\u4f20\u00a0shared_ptr\u00a0\u5c31\u662f\u201c\u5927\u5bb6\u5171\u4eab，\u8c01\u90fd\u522b\u4e71\u5220\u201d\u3002\u6790\u6784\u51fd\u6570\u636e\u6b64\u4e8c\u9009\u4e00\u3002\u6240\u6709\u6743\u5728\u7c7b\u578b\u7b7e\u540d\u91cc\u662f\u663e\u5f0f\u7684，\u4e0d\u9760\u6ce8\u91ca\u3001\u4e0d\u9760\u53e3\u5934\u7ea6\u5b9a\u3002\u00a0\u8fd9\u662f C++ \u63a5\u53e3\u8bbe\u8ba1\u7684\u4e00\u6761\u786c\u529f\u5e95：\u51e1\u662f\u6d89\u53ca\u201c\u8c01\u5220\u8fd9\u5757\u5185\u5b58\u201d\u7684\u5730\u65b9，\u8ba9\u7c7b\u578b\u81ea\u5df1\u628a\u7b54\u6848\u8bf4\u51fa\u6765\u3002<\/p>\n

      \u6700\u540e\u6536\u4e00\u4e0b\u7b2c\u4e8c\u90e8\u5206，\u628a\u8fd9\u53f0\u5f15\u64ce\u7684 API \u9762\u5207\u6210\u4e09\u5c42，\u4f60\u81ea\u7814\u65f6\u4e5f\u8be5\u8fd9\u4e48\u5207：<\/p>\n\n\n\n

      \u5c42<\/p>\n

      \u662f\u4ec0\u4e48<\/p>\n

      \u5bf9\u5916\u5951\u7ea6<\/p>\n<\/tr>\n

      \n\n\n
      \n

      \u7a33\u5b9a\u516c\u5171 API<\/p>\n<\/td>\n

      		\n

      include\/\u00a0\u4e0b\u7684\u7eaf\u865a\u00a0DB\u00a0\/\u00a0Status\u00a0\/\u00a0Comparator\u00a0\/\u00a0Iterator<\/p>\n<\/td>\n

      		\n

      \u7248\u672c\u95f4\u4e0d\u7834\u574f，\u5916\u90e8\u4ee3\u7801\u4f9d\u8d56\u5b83<\/p>\n<\/td>\n<\/tr>\n

      \n

      \u5185\u90e8\u5b9e\u73b0<\/p>\n<\/td>\n

      		\n

      DBImpl\u00a0\u53ca\u5176\u00a0GetImpl，\u6563\u5728\u5341\u51e0\u4e2a\u00a0.cc\u00a0\u91cc<\/p>\n<\/td>\n

      		\n

      \u968f\u65f6\u53ef\u91cd\u6784，\u5916\u4eba\u770b\u4e0d\u89c1<\/p>\n<\/td>\n<\/tr>\n

      \n

      \u6d4b\u8bd5\u8f85\u52a9 API<\/p>\n<\/td>\n

      		\n

      DBImpl\u00a0\u91cc 61 \u4e2a\u00a0TEST_\u00a0\u65b9\u6cd5<\/p>\n<\/td>\n

      		\n

      \u53ea\u7ed9\u5355\u5143\u6d4b\u8bd5，\u9760\u00a0TEST_\u00a0\u524d\u7f00\u9694\u79bb<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

      \u524d\u4e24\u5c42\u7b2c 6 \u8282\u8bb2\u900f\u4e86\u3002\u7b2c\u4e09\u5c42\u662f\u5f88\u591a\u4eba\u81ea\u7814\u65f6\u6f0f\u6389\u7684\u4e00\u5757\u2014\u2014\u6d4b\u8bd5\u9700\u8981\u6345\u8fdb\u5b9e\u73b0\u5185\u90e8\u53bb\u9a8c\u8bc1\u72b6\u6001，\u4f46\u8fd9\u4e9b\u6345\u8fdb\u53bb\u7684\u53e3\u5b50\u7edd\u4e0d\u80fd\u6df7\u8fdb\u516c\u5171 API\u3002\u8fd9\u53f0\u5f15\u64ce\u7684\u505a\u6cd5\u662f\u7ed9\u5b83\u4eec\u7edf\u4e00\u52a0\u00a0TEST_\u00a0\u524d\u7f00，db_impl.h \u91cc\u6570\u4e00\u4e0b\u6709\u516d\u5341\u591a\u4e2a：<\/p>\n

      C++<\/p>\n

      \/\/ db_impl.h：\u6e05\u4e00\u8272 TEST_ \u524d\u7f00，\u53ea\u670d\u52a1\u5355\u5143\u6d4b\u8bd5
      \nSequenceNumber TEST_GetLastVisibleSequence() const;
      \nStatus TEST_FlushMemTable(bool wait = true, bool allow_write_stall = false, …);
      \nStatus TEST_WaitForCompact();
      \nvoid TEST_LockMutex();<\/p>\n

      TEST_GetLastVisibleSequence\u00a0\u76f4\u63a5\u638f\u51fa\u5f53\u524d\u6700\u65b0\u53ef\u89c1\u7684\u7248\u672c\u53f7，TEST_FlushMemTable\u00a0\u624b\u52a8\u903c\u4e00\u6b21\u5185\u5b58\u8868\u843d\u76d8，TEST_WaitForCompact\u00a0\u6b7b\u7b49\u540e\u53f0\u538b\u7f29\u5e72\u5b8c\u2014\u2014\u5168\u662f\u6d4b\u8bd5\u7528\u6765\u628a\u4e0d\u786e\u5b9a\u7684\u540e\u53f0\u65f6\u5e8f\u9489\u6210\u786e\u5b9a\u72b6\u6001\u7684\u94a9\u5b50\u3002\u524d\u7f00\u00a0TEST_\u00a0\u662f\u4e00\u53e5\u4e00\u773c\u53ef\u8fa8\u7684\u58f0\u660e：\u8fd9\u662f\u5b9e\u73b0\u7559\u7ed9\u81ea\u5df1\u4eba\u9a8c\u8bc1\u5185\u90e8\u72b6\u6001\u7684\u540e\u95e8，\u7edd\u4e0d\u5bf9\u5916\u5f00\u653e\u3002\u00a0\u4f60\u81ea\u7814\u5f15\u64ce\u8fdf\u65e9\u4e5f\u8981\u8fd9\u7c7b\u540e\u95e8，\u65e9\u70b9\u7ea6\u5b9a\u4e00\u4e2a\u524d\u7f00\u628a\u5b83\u4eec\u548c\u516c\u5171 API \u9694\u5f00，\u522b\u8ba9\u67d0\u4e2a\u6d4b\u8bd5\u8f85\u52a9\u51fd\u6570\u54ea\u5929\u4e0d\u5c0f\u5fc3\u88ab\u5916\u90e8\u7528\u6237\u4f9d\u8d56\u4e0a，\u90a3\u5c31\u518d\u4e5f\u5220\u4e0d\u6389\u4e86\u3002<\/p>\n

      \n

      9. Open\u3001\u53e5\u67c4\u3001\u5173\u5e93：\u8c01\u62e5\u6709\u8c01，\u8c01\u5fc5\u987b\u5148\u6b7b<\/h3>\n

      \u7b2c\u4e09\u90e8\u5206\u53ea\u56de\u7b54\u4e00\u4e2a\u95ee\u9898：\u8fd9\u5957\u63a5\u53e3\u91cc\u7684\u5bf9\u8c61，\u4ec0\u4e48\u65f6\u5019\u751f，\u4ec0\u4e48\u65f6\u5019\u624d\u5141\u8bb8\u6b7b\u3002\u8fd9\u95ee\u9898\u5bf9\u81ea\u7814\u5f15\u64ce\u662f\u751f\u6b7b\u6538\u5173\u7684\u2014\u2014\u53e5\u67c4\u7684\u6240\u6709\u6743\u5207\u9519\u4e00\u5200，\u8981\u4e48\u6cc4\u6f0f，\u8981\u4e48\u4e8c\u6b21\u91ca\u653e，\u90fd\u662f\u6df1\u591c\u6392\u67e5\u7684\u5e38\u5ba2\u3002<\/p>\n

      \u4ece\u5e93\u672c\u8eab\u5f00\u59cb\u3002Open\u00a0\u4ea4\u8fd8\u7684\u662f\u00a0unique_ptr<DB>，\u72ec\u5360\u6240\u6709\u6743，RAII \u515c\u5e95：<\/p>\n

      C++<\/p>\n

      std::unique_ptr<DB> db;
      \nStatus s = DB::Open(options, "\/tmp\/kv", &db);
      \n\/\/ … \u7528 db …
      \ndb.reset(); \/\/ \u6216\u8005\u79bb\u5f00\u4f5c\u7528\u57df\u81ea\u52a8\u6790\u6784<\/p>\n

      db\u00a0\u4e00\u6790\u6784，\u5e93\u5c31\u5173\u4e86，\u5e72\u51c0\u3002\u4f46\u5e93\u4e0d\u662f\u5b64\u96f6\u96f6\u4e00\u4e2a\u5bf9\u8c61，\u5b83\u4e0b\u9762\u6302\u7740\u4e00\u4e32\u53e5\u67c4，\u8fd9\u4e9b\u53e5\u67c4\u7684\u6b7b\u6d3b\u5f97\u4f60\u81ea\u5df1\u7ba1\u3002\u770b\u5217\u65cf\u8fd9\u4e2a\u4f8b\u5b50\u7684\u5b8c\u6574\u751f\u6b7b\u6d41\u7a0b：<\/p>\n

      C++<\/p>\n

      \/\/ \u5efa\u4e00\u4e2a\u5217\u65cf，\u62ff\u5230\u4e00\u4e2a\u88f8\u6307\u9488\u53e5\u67c4
      \nColumnFamilyHandle* cf;
      \nStatus s = db->CreateColumnFamily(ColumnFamilyOptions(), "new_cf", &cf);
      \n\/\/ … \u7528 cf \u505a\u8bfb\u5199 …
      \n\/\/ \u5173\u5e93\u4e4b\u524d，\u5fc5\u987b\u4eb2\u624b\u628a\u53e5\u67c4\u9500\u6bc1
      \ns = db->DestroyColumnFamilyHandle(cf);
      \ndb.reset();<\/p>\n

      \u6ce8\u610f\u00a0CreateColumnFamily\u00a0\u7ed9\u4f60\u7684\u662f\u4e00\u4e2a\u88f8\u6307\u9488\u00a0ColumnFamilyHandle*，\u4e0d\u662f\u667a\u80fd\u6307\u9488\u3002\u5b83\u7ed9\u88f8\u6307\u9488\u6709\u9053\u7406：\u53e5\u67c4\u6d3b\u591a\u4e45，\u7531\u4f60\u7684\u4e1a\u52a1\u903b\u8f91\u8bf4\u4e86\u7b97，\u5b83\u66ff\u4f60\u51b3\u5b9a\u4e0d\u4e86\u3002\u4e8e\u662f\u6240\u6709\u6743\u660e\u786e\u843d\u5230\u4f60\u5934\u4e0a：\u4f60\u5efa\u7684\u53e5\u67c4，\u4f60\u8d1f\u8d23\u8c03\u00a0DestroyColumnFamilyHandle\u00a0\u9500\u6bc1，\u800c\u4e14\u5fc5\u987b\u5728\u5173\u5e93\u4e4b\u524d\u3002db.h \u90a3\u53e5\u8bdd\u662f\u786c\u8981\u6c42：<\/p>\n

      C++<\/p>\n

      \/\/ db.h：Before destroying the DB, you have to close all column
      \n\/\/ families by calling DestroyColumnFamilyHandle() with all the handles.<\/p>\n

      \u591a\u5217\u65cf\u6253\u5f00\u65f6，\u8fd9\u5957\u6240\u6709\u6743\u5c31\u662f\u4e00\u4e32：<\/p>\n

      C++<\/p>\n

      std::vector<ColumnFamilyHandle*> handles;
      \ns = DB::Open(DBOptions(), "\/tmp\/kv", column_families, &handles, &db);
      \n\/\/ … \u7528 handles[i] \u8bfb\u5199\u5404\u4e2a\u5217\u65cf …
      \nfor (auto handle : handles) {
      \n s = db->DestroyColumnFamilyHandle(handle); \/\/ \u9010\u4e2a\u9500\u6bc1
      \n}
      \ndb.reset(); \/\/ \u53e5\u67c4\u5168\u6e05\u5b8c，\u624d\u5173\u5e93<\/p>\n

      \u8fd9\u91cc\u6709\u4e2a\u53cd\u76f4\u89c9\u7684\u4f8b\u5916，\u5f97\u6572\u4e00\u4e0b：\u9ed8\u8ba4\u5217\u65cf\u7684\u53e5\u67c4\u4e0d\u8981\u4f60\u9500\u6bc1\u3002db.h \u91cc\u00a0DestroyColumnFamilyHandle\u00a0\u7684\u6ce8\u91ca\u4e13\u95e8\u70b9\u4e86\u540d\u2014\u2014except for DefaultColumnFamily()\u3002\u9ed8\u8ba4\u5217\u65cf\u7684\u53e5\u67c4\u7531\u5e93\u81ea\u5df1\u6301\u6709\u548c\u91ca\u653e，\u4f60\u53bb\u00a0Destroy\u00a0\u5b83\u53cd\u800c\u51fa\u9519\u3002\u8fd9\u7c7b\u201c\u770b\u7740\u4e00\u6837\u3001\u751f\u547d\u5468\u671f\u5f52\u5c5e\u5374\u4e0d\u540c\u201d\u7684\u5bf9\u8c61，\u662f\u81ea\u7814\u5f15\u64ce\u63a5\u53e3\u6700\u5bb9\u6613\u8ba9\u4eba\u8e29\u9519\u7684\u5730\u65b9：\u540c\u6837\u662f\u00a0ColumnFamilyHandle*，\u4f60\u5efa\u7684\u90a3\u4e2a\u5f52\u4f60\u9500\u6bc1，\u5e93\u9001\u4f60\u7684\u90a3\u4e2a\u5f52\u5e93\u9500\u6bc1\u3002<\/p>\n

      \u8fed\u4ee3\u5668\u4e5f\u662f\u540c\u4e00\u5957\u89c4\u77e9，\u800c\u4e14\u5b83\u628a\u201c\u8c01\u5fc5\u987b\u5148\u6b7b\u201d\u8bf4\u5f97\u66f4\u72e0\u3002NewIterator\u00a0\u7684\u6ce8\u91ca：<\/p>\n

      C++<\/p>\n

      \/\/ db.h
      \n\/\/ Caller should delete the iterator when it is no longer needed.
      \n\/\/ The returned iterator should be deleted before this db is destroyed.
      \nvirtual Iterator* NewIterator(const ReadOptions& options,
      \n ColumnFamilyHandle* column_family) = 0;<\/p>\n

      \u8fed\u4ee3\u5668\u5fc5\u987b\u5148\u4e8e\u5e93\u6b7b\u3002\u00a0\u60f3\u60f3\u4e5f\u5bf9：\u8fed\u4ee3\u5668\u662f\u9a91\u5728\u5e93\u7684\u5185\u90e8\u6570\u636e\u7ed3\u6784\u4e0a\u7684\u4e00\u4e2a\u6e38\u6807，\u5e93\u90fd\u6ca1\u4e86，\u5b83\u9a91\u7684\u90a3\u5339\u9a6c\u5c31\u6ca1\u4e86，\u518d\u52a8\u5b83\u5c31\u662f\u8bbf\u95ee\u5df2\u91ca\u653e\u5185\u5b58\u3002\u6240\u4ee5\u6790\u6784\u987a\u5e8f\u6709\u4e00\u6761\u94c1\u5f8b\u2014\u2014\u540e\u501f\u7684\u5148\u8fd8：\u8fed\u4ee3\u5668\u3001\u5217\u65cf\u53e5\u67c4\u8fd9\u4e9b\u4ece\u5e93\u501f\u51fa\u6765\u7684\u5bf9\u8c61，\u5168\u90fd\u5f97\u8d76\u5728\u5e93\u6790\u6784\u4e4b\u524d\u9500\u6bc1\u6389\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u65f6，Open\u00a0\u8fd4\u56de\u00a0unique_ptr\u00a0\u5f88\u5bb9\u6613\u8ba9\u4eba\u4ee5\u4e3a\u201cRAII \u5168\u81ea\u52a8\u4e86\u201d，\u4f46 RAII \u53ea\u7ba1\u597d\u4e86\u5e93\u672c\u8eab；\u90a3\u4e9b\u5e93\u501f\u7ed9\u4f60\u7684\u88f8\u6307\u9488\u53e5\u67c4，\u5f97\u9760\u4f60\u81ea\u5df1\u4fdd\u8bc1\u5b83\u4eec\u6b7b\u5728\u5e93\u524d\u9762\u3002\u628a\u8fd9\u6761\u987a\u5e8f\u5199\u8fdb\u4f60\u7684\u63a5\u53e3\u6ce8\u91ca\u91cc，\u662f\u5bf9\u4e0b\u6e38\u6700\u8d77\u7801\u7684\u4ea4\u4ee3\u3002<\/p>\n

      \u8fd9\u6761\u987a\u5e8f\u9519\u4e86\u4f1a\u600e\u6837，\u6211\u4eec\u8ba9\u5b83\u5d29\u4e00\u6b21：<\/p>\n

      C++<\/p>\n

      std::unique_ptr<DB> db;
      \nDB::Open(options, "\/tmp\/kv", &db);
      \nIterator* it = db->NewIterator(ReadOptions());
      \ndb.reset(); \/\/ \u5e93\u5148\u6790\u6784\u4e86！
      \nit->SeekToFirst(); \/\/ \u6e38\u6807\u8fd8\u9a91\u5728\u5df2\u7ecf\u6ca1\u4e86\u7684\u5185\u90e8\u7ed3\u6784\u4e0a
      \n\/\/ use-after-free：\u8fd0\u6c14\u597d\u5f53\u573a\u6bb5\u9519\u8bef，\u8fd0\u6c14\u574f\u8bfb\u5230\u810f\u6570\u636e\u63a5\u7740\u8dd1
      \ndelete it;<\/p>\n

      db.reset()\u00a0\u628a\u5e93\u8fde\u540c\u5b83\u7684\u5185\u90e8\u7ed3\u6784\u4e00\u8d77\u6790\u6784\u4e86，it\u00a0\u624b\u91cc\u90a3\u6839\u6e38\u6807\u6307\u5411\u7684\u4e1c\u897f\u5df2\u7ecf\u4e0d\u5b58\u5728，SeekToFirst\u00a0\u4e00\u52a8\u5c31\u662f use-after-free\u3002\u6700\u8981\u547d\u7684\u662f\u5b83\u4e0d\u4e00\u5b9a\u5f53\u573a\u5d29\u2014\u2014\u5185\u5b58\u521a\u91ca\u653e\u3001\u8fd8\u6ca1\u88ab\u522b\u4eba\u590d\u7528\u65f6，\u5b83\u53ef\u80fd\u201c\u770b\u8d77\u6765\u6b63\u5e38\u201d\u5730\u8bfb\u51fa\u4e00\u6279\u5783\u573e，\u4f60\u4ee5\u4e3a\u67e5\u8be2\u6210\u529f\u4e86，\u5176\u5b9e\u62ff\u5230\u7684\u662f\u5df2\u91ca\u653e\u5185\u5b58\u91cc\u7684\u6b8b\u6e23\u3002\u8fd9\u7c7b bug \u5728\u81ea\u7814\u5f15\u64ce\u91cc\u6700\u96be\u67e5，\u56e0\u4e3a\u5b83\u662f\u6982\u7387\u6027\u7684\u3001\u548c\u5185\u5b58\u5206\u914d\u5668\u7684\u5373\u65f6\u884c\u4e3a\u8026\u5408，\u6362\u53f0\u673a\u5668\u3001\u6362\u4e2a\u8d1f\u8f7d\u5c31\u4e0d\u590d\u73b0\u3002\u9632\u5b83\u53ea\u6709\u4ece\u63a5\u53e3\u4e0a\u628a\u987a\u5e8f\u9489\u6b7b：\u6240\u6709\u501f\u51fa\u7684\u53e5\u67c4，\u8981\u4e48\u7528 RAII \u5305\u8d77\u6765\u3001\u968f\u4f5c\u7528\u57df\u81ea\u7136\u5148\u4e8e\u5e93\u6790\u6784，\u8981\u4e48\u5728\u5e93\u7684\u6790\u6784\u91cc\u4e3b\u52a8\u67e5\u4e00\u904d\u8fd8\u6709\u6ca1\u6709\u6d3b\u7740\u7684\u501f\u51fa\u5bf9\u8c61\u3001\u6709\u5c31\u5f53\u573a\u62a5\u9519，\u7edd\u4e0d\u8ba9\u5b83\u6084\u6084\u6e9c\u8fc7\u53bb\u3002<\/p>\n

      10. \u201c\u8fd8\u5b58\u5728\u201d\u548c\u201c\u8fd8\u770b\u5f97\u89c1\u201d，\u662f\u4e24\u6839\u72ec\u7acb\u7684\u8f74<\/h3>\n

      \u8fd9\u662f\u7b2c\u4e09\u90e8\u5206\u7684\u6838\u5fc3，\u4e5f\u662f\u6574\u7bc7\u6700\u53cd\u76f4\u89c9\u7684\u4e00\u8282\u3002\u524d\u9762\u6240\u6709\u94fa\u57ab\u2014\u2014\u7b2c 2 \u8282\u7684\u5893\u7891\u3001\u7b2c 5 \u8282\u7684\u201c\u6709\u7248\u672c\u201d\u2014\u2014\u90fd\u662f\u4e3a\u4e86\u8fd9\u4e00\u8282\u80fd\u7ad9\u4f4f\u3002<\/p>\n

      \u5148\u770b\u5217\u65cf\u7684\u201c\u5220\u9664\u201d\u3002\u4f60\u4ee5\u4e3a\u00a0DropColumnFamily\u00a0\u4f1a\u628a\u8fd9\u4e2a\u5217\u65cf\u7684\u6570\u636e\u62b9\u6389，\u770b\u5b83\u7684\u6ce8\u91ca：<\/p>\n

      C++<\/p>\n

      \/\/ db.h：This call only records a drop record in the manifest and
      \n\/\/ prevents the column family from flushing and compacting.
      \nvirtual Status DropColumnFamily(ColumnFamilyHandle* column_family);<\/p>\n

      \u5b83\u53ea\u5e72\u4e24\u4ef6\u4e8b：\u5f80\u5143\u6570\u636e\u91cc\u8bb0\u4e00\u7b14\u201c\u8fd9\u4e2a\u5217\u65cf\u88ab\u5220\u4e86\u201d，\u7136\u540e\u7981\u6b62\u5b83\u7ee7\u7eed\u5237\u76d8\u548c\u538b\u7f29\u3002\u6570\u636e\u4e00\u4e2a\u5b57\u8282\u90fd\u6ca1\u52a8\u3002\u90a3\u8fd9\u4e2a\u5217\u65cf\u4ec0\u4e48\u65f6\u5019\u624d\u771f\u6b63\u6d88\u5931？\u7b54\u6848\u5728\u00a0DestroyColumnFamilyHandle\u00a0\u7684\u6ce8\u91ca\u91cc，\u8fd9\u53e5\u8bdd\u662f\u6574\u7bc7\u7684\u9898\u773c：<\/p>\n

      C++<\/p>\n

      \/\/ db.h：A column family is only removed once it is dropped
      \n\/\/ (DropColumnFamily) and all handles have been destroyed
      \n\/\/ (DestroyColumnFamilyHandle).<\/p>\n

      \u4e00\u4e2a\u5217\u65cf\u771f\u6b63\u88ab\u79fb\u9664，\u8981\u540c\u65f6\u6ee1\u8db3\u4e24\u4e2a\u6761\u4ef6：\u88ab drop \u4e86，\u800c\u4e14\u6240\u6709\u53e5\u67c4\u90fd\u9500\u6bc1\u4e86\u3002\u628a\u8fd9\u4e24\u4e2a\u6761\u4ef6\u62c6\u5f00，\u4f60\u5c31\u649e\u89c1\u4e86\u6574\u53f0\u5b58\u50a8\u5f15\u64ce\u6700\u6838\u5fc3\u7684\u4e00\u7ec4\u6982\u5ff5\u2014\u2014\u201c\u8fd8\u5b58\u5728\u201d\u548c\u201c\u8fd8\u770b\u5f97\u89c1\u201d\u662f\u4e24\u6839\u72ec\u7acb\u7684\u8f74：<\/p>\n

        \n
      • \n

        DropColumnFamily\u00a0\u4e4b\u540e，\u8fd9\u4e2a\u5217\u65cf\u4e0d\u53ef\u89c1\u4e86：\u65b0\u7684\u8bfb\u5199\u8ba4\u4e3a\u5b83\u6ca1\u4e86，\u5b83\u4e0d\u518d\u5237\u76d8\u4e0d\u518d\u538b\u7f29\u3002<\/p>\n<\/li>\n

      • \n

        \u4f46\u53ea\u8981\u8fd8\u6709\u4e00\u4e2a\u53e5\u67c4\u6ca1\u9500\u6bc1，\u5b83\u5c31\u8fd8\u5b58\u5728：\u6570\u636e\u8fd8\u8eba\u5728\u76d8\u4e0a，\u90a3\u4e2a\u53e5\u67c4\u8fd8\u80fd\u8bbf\u95ee\u5230\u5b83\u3002<\/p>\n<\/li>\n<\/ul>\n

        \u53ef\u89c1\u6027\u548c\u5b58\u5728\u6027，\u88ab\u8fd9\u4e24\u4e2a\u52a8\u4f5c\u5207\u6210\u4e86\u4e24\u4ef6\u4e8b\u3002\u8fd9\u4e0d\u662f\u5217\u65cf\u72ec\u6709\u7684\u602a\u7656，\u5b83\u662f\u201c\u6709\u7248\u672c\u201d\u8fd9\u4e2a\u8bcd\u7684\u5fc5\u7136\u7ed3\u679c\u3002\u540c\u4e00\u6839\u8f74，\u5728\u5feb\u7167\u4e0a\u8868\u73b0\u5f97\u66f4\u7eaf\u7cb9\u3002\u5148\u8ba4\u8bc6\u7248\u672c\u53f7，snapshot.h：<\/p>\n

        C++<\/p>\n

        \/\/ snapshot.h
        \n\/\/ Abstract handle to particular state of a DB.
        \nclass Snapshot {
        \n public:
        \n virtual SequenceNumber GetSequenceNumber() const = 0;
        \n};<\/p>\n

        \u4e00\u4e2a\u5feb\u7167，\u672c\u8d28\u5c31\u662f\u4e00\u4e2a\u5e8f\u5217\u53f7\u2014\u2014\u7b2c 5 \u8282\u8bf4\u7684\u90a3\u4e2a\u201c\u6709\u7248\u672c\u201d\u7684\u7248\u672c\u53f7\u3002\u5f15\u64ce\u5185\u90e8\u6bcf\u4e00\u6b21\u5199\u64cd\u4f5c\u90fd\u9886\u4e00\u4e2a\u5355\u8c03\u9012\u589e\u7684\u5e8f\u5217\u53f7，\u4e00\u4e2a\u5feb\u7167\u9489\u4f4f\u67d0\u4e2a\u5e8f\u5217\u53f7，\u610f\u601d\u662f\u201c\u6211\u8981\u770b\u8fd9\u53f0\u5e93\u5728\u8fd9\u4e2a\u5e8f\u5217\u53f7\u90a3\u4e00\u523b\u7684\u6837\u5b50\u201d\u3002db.h \u91cc\u00a0GetSnapshot\u00a0\u7684\u7ea6\u5b9a：<\/p>\n

        C++<\/p>\n

        \/\/ db.h：Return a handle to the current DB state. Iterators created
        \n\/\/ with this handle will all observe a stable snapshot of the current
        \n\/\/ DB state. The caller must call ReleaseSnapshot(result) when the
        \n\/\/ snapshot is no longer needed.
        \nvirtual const Snapshot* GetSnapshot() = 0;<\/p>\n

        \u73b0\u5728\u201c\u5b58\u5728\u4e0e\u53ef\u89c1\u201d\u8fd9\u6761\u7ebf\u5f7b\u5e95\u663e\u5f62\u4e86\u3002\u753b\u4e00\u6761\u65f6\u95f4\u8f74：<\/p>\n

        text<\/p>\n

        \u5e8f\u5217\u53f7: 100 105 110
        \n \u2502Put k=v1 \u2502Delete k \u2502(\u6b64\u523b)
        \n \u25bc \u25bc \u25bc
        \n\u6301\u6709\u4e00\u4e2a seq=100 \u7684\u5feb\u7167\u7684\u8bfb\u8005：
        \n \u2192 \u7167\u6837\u8bfb\u5230 k=v1（\u5bf9\u4ed6，v1 \u8fd8\u3010\u53ef\u89c1\u3011）
        \n\u4e0d\u6301\u5feb\u7167\u3001\u8bfb\u6700\u65b0\u7684\u8bfb\u8005：
        \n \u2192 \u8bfb k \u5f97\u5230 NotFound（\u5bf9\u4ed6，k \u5df2\u3010\u4e0d\u53ef\u89c1\u3011）
        \n\u800c v1 \u8fd9\u6761\u6570\u636e：
        \n \u2192 \u4e00\u76f4\u3010\u5b58\u5728\u3011\u5728\u76d8\u4e0a，\u56e0\u4e3a\u90a3\u4e2a\u5feb\u7167\u8fd8\u9489\u7740\u5b83<\/p>\n

        Delete k\u00a0\u4e4b\u540e，\u5bf9\u8bfb\u6700\u65b0\u72b6\u6001\u7684\u4eba，k\u00a0\u5df2\u7ecf\u4e0d\u53ef\u89c1\u4e86\u3002\u4f46\u90a3\u4e2a\u6301\u6709 seq=100 \u5feb\u7167\u7684\u8bfb\u8005，\u7167\u6837\u80fd\u8bfb\u5230\u00a0v1\u2014\u2014\u56e0\u4e3a\u5bf9\u4ed6\u6765\u8bf4，\u5220\u9664\u53d1\u751f\u5728\u201c\u672a\u6765\u201d，\u8fd8\u6ca1\u8f6e\u5230\u3002\u4e8e\u662f\u00a0v1\u00a0\u8fd9\u6761\u88ab\u5220\u7684\u6570\u636e\u5fc5\u987b\u7ee7\u7eed\u5b58\u5728，\u7269\u7406\u4e0a\u4e0d\u80fd\u88ab\u538b\u7f29\u56de\u6536\u6389，\u76f4\u5230\u90a3\u4e2a\u5feb\u7167\u88ab\u91ca\u653e\u3002\u5feb\u7167 pin \u4f4f\u7684\u662f\u53ef\u89c1\u6027\u548c\u53ef\u56de\u6536\u6027，\u4e0d\u662f\u5b58\u5728\u6027\u672c\u8eab\u2014\u2014\u53cd\u8fc7\u6765\u8bf4，\u4e00\u4e2a\u6ca1\u91ca\u653e\u7684\u5feb\u7167，\u4f1a\u628a\u4e00\u5927\u7968\u201c\u903b\u8f91\u4e0a\u65e9\u8be5\u6d88\u5931\u201d\u7684\u65e7\u7248\u672c\u6570\u636e\u9489\u5728\u78c1\u76d8\u4e0a，\u8c01\u90fd\u5220\u4e0d\u6389\u3002\u8fd9\u5c31\u662f\u81ea\u7814 MVCC \u5f15\u64ce\u7ed5\u4e0d\u5f00\u7684\u53d6\u820d：\u8bfb\u7684\u4e00\u81f4\u6027，\u662f\u7528\u63a8\u8fdf\u56de\u6536\u65e7\u7248\u672c\u7684\u7a7a\u95f4\u6362\u6765\u7684\u3002<\/p>\n

        \u8fd9\u4e2a\u4ee3\u4ef7\u5728\u540e\u53f0\u8fd8\u6709\u66f4\u786c\u7684\u4e00\u9762\u3002\u5f15\u64ce\u7684\u540e\u53f0\u538b\u7f29\u8981\u56de\u6536\u65e7\u7248\u672c\u2014\u2014\u4e00\u4e2a key \u88ab\u8986\u76d6\u6216\u5220\u9664\u540e，\u5b83\u7684\u65e7\u7248\u672c\u8fdf\u65e9\u5f97\u7269\u7406\u6e05\u6389，\u5426\u5219\u78c1\u76d8\u53ea\u6da8\u4e0d\u843d\u3002\u53ef\u538b\u7f29\u4e0d\u80fd\u968f\u4fbf\u6e05：\u53ea\u8981\u8fd8\u6709\u4e00\u4e2a\u5feb\u7167\u9489\u7740\u67d0\u4e2a\u65e7\u5e8f\u5217\u53f7，\u6bd4\u5b83\u65b0\u7684\u5220\u9664\u5c31\u4e0d\u80fd\u771f\u6b63\u751f\u6548，\u88ab\u5220\u7684\u6570\u636e\u4e5f\u4e0d\u80fd\u771f\u6b63\u56de\u6536\u3002\u4e8e\u662f\u6700\u8001\u7684\u90a3\u4e2a\u672a\u91ca\u653e\u5feb\u7167\u7684\u5e8f\u5217\u53f7，\u5c31\u662f\u6574\u53f0\u5f15\u64ce\u7684\u56de\u6536\u6c34\u4f4d\u7ebf\u2014\u2014\u538b\u7f29\u53ea\u80fd\u5b89\u5168\u6e05\u7406\u8fd9\u6761\u6c34\u4f4d\u7ebf\u4ee5\u4e0b\u3001\u4e14\u786e\u5b9e\u6ca1\u6709\u5feb\u7167\u518d\u5173\u5fc3\u7684\u7248\u672c\u3002\u4e00\u4e2a\u5fd8\u4e86\u91ca\u653e\u3001\u8dd1\u4e86\u4e00\u6574\u5929\u7684\u5feb\u7167，\u4f1a\u628a\u6c34\u4f4d\u7ebf\u6b7b\u6b7b\u710a\u5728\u4e00\u5929\u524d，\u8fd9\u4e00\u5929\u91cc\u6240\u6709\u88ab\u5220\u3001\u88ab\u8986\u76d6\u7684\u6570\u636e\u5168\u90fd\u6e05\u4e0d\u6389，\u78c1\u76d8\u5360\u7528\u8089\u773c\u53ef\u89c1\u5730\u5f80\u4e0a\u6da8\u3002\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u957f\u547d\u5feb\u7167\u5728\u5b58\u50a8\u5f15\u64ce\u91cc\u662f\u5934\u53f7\u8fd0\u7ef4\u4e8b\u6545\u6e90，\u4e5f\u662f\u4e3a\u4ec0\u4e48\u5173\u5e93\u65f6\u90a3\u9053\u201c\u6709\u672a\u91ca\u653e\u5feb\u7167\u5c31\u00a0Abort\u201d\u7684\u95e8\u7981\u5fc5\u987b\u5b58\u5728\u2014\u2014\u5b83\u62e6\u4e0b\u7684\u4e0d\u53ea\u662f\u4e00\u6b21\u5173\u5e93，\u662f\u5728\u63d0\u9192\u4f60：\u6709\u4e00\u4e2a\u6b63\u6084\u6084\u6491\u7206\u78c1\u76d8\u7684\u5f15\u7528\u8fd8\u6ca1\u8fd8\u3002\u4f60\u81ea\u7814 MVCC \u5f15\u64ce\u65f6，\u628a\u201c\u6700\u8001\u5feb\u7167\u5e8f\u5217\u53f7\u201d\u505a\u6210\u4e00\u4e2a\u80fd\u76d1\u63a7\u3001\u80fd\u544a\u8b66\u7684\u6307\u6807，\u6bd4\u5927\u591a\u6570\u82b1\u54e8\u4f18\u5316\u90fd\u503c\u3002<\/p>\n

        \u8fd9\u4e2a\u4ee3\u4ef7\u4f1a\u5728\u5173\u5e93\u65f6\u5f53\u9762\u627e\u4e0a\u4f60\u3002\u6211\u4eec\u8ba9\u5b83\u5d29\u4e00\u6b21：<\/p>\n

        C++<\/p>\n

        const Snapshot* snap = db->GetSnapshot();
        \n\/\/ … \u7528 snap \u8bfb\u4e86\u4e00\u4f1a\u513f，\u7136\u540e\u5fd8\u4e86\u8fd8 …<\/p>\n

        Status s = db->Close();
        \n\/\/ s.IsAborted() == true \u2014\u2014 \u5173\u4e0d\u6389！<\/p>\n

        Close\u00a0\u76f4\u63a5\u8fd4\u56de\u00a0Aborted，\u5e93\u5173\u4e0d\u6389\u3002db.h \u91cc\u00a0Close\u00a0\u7684\u6ce8\u91ca\u628a\u539f\u56e0\u548c\u89e3\u6cd5\u90fd\u7ed9\u4e86：<\/p>\n

        C++<\/p>\n

        \/\/ db.h：If the return status is Aborted(), closing fails because
        \n\/\/ there is unreleased snapshot in the system. In this case, users
        \n\/\/ can release the unreleased snapshots and try again and expect it
        \n\/\/ to succeed.<\/p>\n

        \u4e00\u4e2a\u6ca1\u91ca\u653e\u7684\u5feb\u7167，\u4f1a\u628a\u5173\u5e93\u6574\u4e2a\u62e6\u4e0b\u6765\u2014\u2014\u56e0\u4e3a\u5e93\u4e00\u65e6\u5173\u4e86，\u90a3\u4e2a\u5feb\u7167\u9489\u7740\u7684\u65e7\u7248\u672c\u5185\u5b58\u548c\u6587\u4ef6\u5c31\u90fd\u6ca1\u4e86，\u5f15\u64ce\u5b81\u53ef\u62d2\u7edd\u5173\u5e93\u4e5f\u4e0d\u5236\u9020\u8fd9\u79cd\u60ac\u7a7a\u3002\u89e3\u6cd5\u662f\u5148\u8fd8\u5feb\u7167：<\/p>\n

        C++<\/p>\n

        db->ReleaseSnapshot(snap); \/\/ \u5148\u628a\u53ef\u89c1\u6027\u5f15\u7528\u8fd8\u56de\u53bb
        \ns = db->Close(); \/\/ \u73b0\u5728\u80fd\u5173\u4e86<\/p>\n

        \u90a3\u80fd\u4e0d\u80fd\u5e72\u8106\u00a0delete snap？\u4e0d\u80fd，\u7f16\u8bd1\u5668\u4e0d\u8ba9\u3002\u770b snapshot.h：<\/p>\n

        C++<\/p>\n

        \/\/ snapshot.h
        \nclass Snapshot {
        \n protected:
        \n virtual ~Snapshot(); \/\/ \u6790\u6784\u51fd\u6570\u662f protected！
        \n};<\/p>\n

        \u6790\u6784\u51fd\u6570\u662f\u00a0protected\u00a0\u7684，\u4f60\u5728\u5916\u9762\u00a0delete snap\u00a0\u76f4\u63a5\u7f16\u8bd1\u4e0d\u8fc7\u3002\u8fd9\u662f\u4e00\u9053\u7f16\u8bd1\u671f\u7684\u5f3a\u5236\u2014\u2014\u5feb\u7167\u7684\u91ca\u653e\u53ea\u80fd\u8d70\u00a0ReleaseSnapshot\u00a0\u8fd9\u4e00\u4e2a\u53e3\u5b50，\u56e0\u4e3a\u91ca\u653e\u5feb\u7167\u4e0d\u53ea\u662f\u5220\u4e2a\u5bf9\u8c61，\u8fd8\u8981\u901a\u77e5\u5f15\u64ce\u201c\u8fd9\u4e2a\u5e8f\u5217\u53f7\u6211\u4e0d\u9489\u4e86，\u4f60\u53ef\u4ee5\u56de\u6536\u5bf9\u5e94\u7684\u65e7\u7248\u672c\u4e86\u201d\u3002delete\u00a0\u5e72\u4e0d\u4e86\u540e\u534a\u4ef6\u4e8b，\u6240\u4ee5\u5e72\u8106\u4ece\u7c7b\u578b\u5c42\u9762\u7981\u6389\u3002\u60f3\u8981 RAII \u7684\u7701\u5fc3，\u5b83\u7ed9\u4e86\u4e2a\u5305\u88c5：<\/p>\n

        C++<\/p>\n

        \/\/ snapshot.h
        \n\/\/ Simple RAII wrapper class for Snapshot.
        \nclass ManagedSnapshot {
        \n public:
        \n explicit ManagedSnapshot(DB* db); \/\/ \u6784\u9020\u5373 GetSnapshot
        \n ~ManagedSnapshot(); \/\/ \u6790\u6784\u5373 ReleaseSnapshot
        \n};<\/p>\n

        \u6784\u9020\u65f6\u62ff\u5feb\u7167，\u6790\u6784\u65f6\u81ea\u52a8\u00a0ReleaseSnapshot\u2014\u2014\u628a\u201c\u5fc5\u987b\u6210\u5bf9\u8c03\u7528\u3001\u5426\u5219\u5173\u4e0d\u6389\u5e93\u201d\u7684\u624b\u52a8\u534f\u8bae，\u5305\u6210\u4e00\u4e2a\u79bb\u5f00\u4f5c\u7528\u57df\u81ea\u52a8\u5f52\u8fd8\u7684\u5bf9\u8c61\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u91cc\u51e1\u662f\u8fd9\u79cd\u201c\u501f\u4e86\u5fc5\u987b\u8fd8\u3001\u8fd8\u9519\u4e86\u6216\u5fd8\u8fd8\u4f1a\u62d6\u4f4f\u7cfb\u7edf\u201d\u7684\u8d44\u6e90，\u90fd\u8be5\u987a\u624b\u914d\u4e00\u4e2a\u8fd9\u6837\u7684 RAII \u5305\u88c5，\u522b\u628a\u6210\u5bf9\u8c03\u7528\u7684\u7eaa\u5f8b\u7559\u7ed9\u8c03\u7528\u65b9\u7684\u8bb0\u6027\u3002<\/p>\n

        11. Slice\u3001pin \u4e0e Cache Handle：\u501f\u51fa\u53bb\u7684\u5185\u5b58\u4ec0\u4e48\u65f6\u5019\u5931\u6548<\/h3>\n

        \u751f\u547d\u5468\u671f\u8fd8\u6709\u6700\u7ec6\u7684\u4e00\u5c42，\u7ec6\u5230\u5355\u4e2a\u00a0Slice\u00a0\u6307\u5411\u7684\u90a3\u51e0\u5341\u4e2a\u5b57\u8282\u3002\u8fd9\u4e00\u5c42\u76f4\u63a5\u8fde\u7740\u4f60\u8981\u7684\u78c1\u76d8 IO \u4e0e\u7f13\u5b58\u7b56\u7565，\u662f\u63a5\u53e3\u548c\u6027\u80fd\u7684\u4ea4\u754c\u9762\u3002<\/p>\n

        \u5148\u5d29\u4e00\u4e2a\u6700\u5e38\u89c1\u7684\u3002\u4f60\u60f3\u5728\u904d\u5386\u65f6\u628a\u67d0\u4e2a key \u5b58\u4e0b\u6765\u5f85\u4f1a\u513f\u7528：<\/p>\n

        C++<\/p>\n

        Slice saved_key = it->key(); \/\/ \u5b58\u4e0b\u5f53\u524d key
        \nit->Next(); \/\/ \u6e38\u6807\u5f80\u524d\u8d70\u4e00\u6b65
        \nuse(saved_key); \/\/ \u60ac\u7a7a！saved_key \u6307\u5411\u7684\u5185\u5b58\u5df2\u88ab\u590d\u7528<\/p>\n

        saved_key\u00a0\u5728\u00a0Next()\u00a0\u4e4b\u540e\u5c31\u662f\u4e00\u4e2a\u60ac\u7a7a\u5f15\u7528\u3002\u4e3a\u4ec0\u4e48？iterator_base.h \u7684\u00a0key()\u00a0\u6ce8\u91ca：<\/p>\n

        C++<\/p>\n

        \/\/ iterator_base.h：The underlying storage for the returned slice is
        \n\/\/ valid only until the next modification of the iterator (i.e. the
        \n\/\/ next SeekToFirst\/SeekToLast\/Seek\/SeekForPrev\/Next\/Prev operation).
        \nvirtual Slice key() const = 0;<\/p>\n

        key()\u00a0\u548c\u00a0value()\u00a0\u8fd4\u56de\u7684\u00a0Slice\u00a0\u53ea\u662f\u6307\u5411\u5f15\u64ce\u5185\u90e8\u7f13\u51b2\u533a\u7684\u4e00\u4e2a\u89c6\u56fe，\u4e0d\u62e5\u6709\u5185\u5b58\u3002\u6e38\u6807\u4e00\u52a8，\u90a3\u5757\u7f13\u51b2\u533a\u5c31\u88ab\u4e0b\u4e00\u4e2a key \u590d\u7528\u4e86，\u4f60\u4e4b\u524d\u5b58\u7684\u00a0Slice\u00a0\u7acb\u523b\u5931\u6548\u3002\u8fd9\u662f\u96f6\u62f7\u8d1d\u8fed\u4ee3\u7684\u4ee3\u4ef7\u2014\u2014\u5b83\u4e0d\u7ed9\u4f60\u62f7\u8d1d，\u6362\u6765\u7684\u662f\u4f60\u5fc5\u987b\u5728\u6e38\u6807\u79fb\u52a8\u524d\u628a\u8981\u7559\u7684\u6570\u636e\u81ea\u5df1\u62f7\u8d70（it->key().ToString()\u00a0\u5b58\u6210\u00a0std::string）\u3002\u8fd9\u4e2a\u5751\u5728\u81ea\u7814\u5f15\u64ce\u91cc\u51e0\u4e4e\u4eba\u4eba\u8e29\u4e00\u904d，\u56e0\u4e3a\u00a0Slice\u00a0\u957f\u5f97\u592a\u50cf\u00a0string_view，\u4f60\u4f1a\u4e0b\u610f\u8bc6\u4ee5\u4e3a\u5b83\u4e00\u76f4\u6709\u6548\u3002\u5343\u4e07\u8bb0\u4f4f：\u4ece\u6e38\u6807\u501f\u51fa\u6765\u7684\u00a0Slice，\u5bff\u547d\u53ea\u5230\u4e0b\u4e00\u6b21\u79fb\u52a8\u6e38\u6807\u3002<\/p>\n

        \u540c\u6837\u7684\u201c\u501f\u51fa\u5185\u5b58\u201d\u903b\u8f91，\u5728\u70b9\u67e5\u8fd9\u4fa7\u5c31\u662f\u7b2c 1 \u8282\u89c1\u8fc7\u7684\u00a0PinnableSlice\u3002\u56de\u770b\u90a3\u6bb5\u4ee3\u7801，\u73b0\u5728\u4f60\u80fd\u8bfb\u61c2\u5b83\u6bcf\u4e00\u884c\u4e86：<\/p>\n

        C++<\/p>\n

        PinnableSlice pinnable_val;
        \ndb->Get(ReadOptions(), db->DefaultColumnFamily(), "key2", &pinnable_val);
        \n\/\/ pinnable_val \u76f4\u63a5\u6307\u5411\u7f13\u5b58\u91cc\u90a3\u4efd value，\u4e00\u6b21\u62f7\u8d1d\u90fd\u6ca1\u6709
        \nassert(pinnable_val == "value");<\/p>\n

        pinnable_val.Reset();
        \n\/\/ The Slice pointed by pinnable_val is not valid after this point<\/p>\n

        PinnableSlice\u00a0\u662f\u4e3a\u4e86\u7701\u6389\u00a0Get\u00a0\u90a3\u6b21\u503c\u62f7\u8d1d\u3002\u666e\u901a\u7684\u00a0Get(…, std::string* value)\u00a0\u4f1a\u628a\u503c\u4ece\u7f13\u5b58\u62f7\u8fdb\u4f60\u7684 string；PinnableSlice\u00a0\u4e0d\u62f7，\u5b83\u76f4\u63a5pin \u4f4f\u7f13\u5b58\u91cc\u90a3\u4efd\u503c\u2014\u2014\u5728\u4f60\u00a0Reset\u00a0\u4e4b\u524d，\u90a3\u4efd\u503c\u6240\u5728\u7684\u7f13\u5b58\u5757\u4e0d\u8bb8\u88ab\u6dd8\u6c70，\u4f60\u624b\u91cc\u7684\u00a0Slice\u00a0\u5c31\u4e00\u76f4\u6307\u7740\u5b83\u6709\u6548\u3002\u7528\u5b8c\u5fc5\u987b\u00a0Reset，\u628a pin \u89e3\u5f00\u3002<\/p>\n

        \u8fd9\u91cc\u5c31\u5192\u51fa\u4e86\u4f60\u8981\u7684\u201c\u7f13\u5b58\u7b56\u7565\u201d\u548c\u63a5\u53e3\u751f\u547d\u5468\u671f\u7684\u4ea4\u754c\u70b9\u3002pin \u4f4f\u4e00\u4efd\u7f13\u5b58\u503c，\u5e95\u4e0b\u5bf9\u5e94\u7684\u662f pin \u4f4f\u4e00\u4e2a\u00a0Cache Handle\u2014\u2014\u7f13\u5b58\u91cc\u90a3\u4e2a\u6570\u636e\u5757\u7684\u5f15\u7528\u3002\u8fd9\u4e2a\u5f15\u7528\u7684\u4ee3\u4ef7\u662f\u8fd9\u6837\u7684：<\/p>\n

          \n
        • \n

          \u4e00\u4e2a\u5757\u88ab pin \u4f4f，\u5b83\u5c31\u4e0d\u80fd\u88ab\u7f13\u5b58\u6dd8\u6c70，\u54ea\u6015\u7f13\u5b58\u5df2\u7ecf\u6ee1\u4e86\u3001\u8fd9\u4e2a\u5757\u662f\u6700\u8be5\u88ab\u8e22\u51fa\u53bb\u7684\u51b7\u5757，\u53ea\u8981\u8fd8\u6709\u4e00\u4e2a pin \u6ca1\u89e3\u5f00，\u5b83\u5c31\u5f97\u5728\u7f13\u5b58\u91cc\u5360\u7740\u3002<\/p>\n<\/li>\n

        • \n

          \u4e8e\u662f\u201c\u501f\u51fa\u4e00\u4efd\u96f6\u62f7\u8d1d\u7684\u503c\u201d\u8fd9\u4e2a\u4fbf\u5229，\u4ee3\u4ef7\u662f\u5ef6\u957f\u4e86\u4e00\u4e2a\u7f13\u5b58\u5757\u7684\u5bff\u547d\u3001\u5360\u4f4f\u4e86\u4e00\u683c\u7f13\u5b58\u3002\u4f60\u8981\u662f\u62ff\u4e00\u5806\u00a0PinnableSlice\u00a0\u8fdf\u8fdf\u4e0d\u00a0Reset，\u7b49\u4e8e\u628a\u4e00\u6279\u7f13\u5b58\u5757\u9489\u6b7b，\u7f13\u5b58\u7684\u6709\u6548\u5bb9\u91cf\u88ab\u4f60\u6084\u6084\u5403\u6389，\u547d\u4e2d\u7387\u5f80\u4e0b\u6389\u3002<\/p>\n<\/li>\n<\/ul>\n

          \u770b\u5230\u8fd9\u6761\u7ebf\u4e86\u5417\u2014\u2014\u5b83\u548c\u7b2c 10 \u8282\u7684\u5feb\u7167\u662f\u540c\u4e00\u4e2a\u9053\u7406，\u6362\u4e86\u4e2a\u5c3a\u5ea6：\u5feb\u7167 pin \u4f4f\u7684\u662f\u6574\u4e2a\u5e93\u67d0\u4e2a\u7248\u672c\u7684\u53ef\u56de\u6536\u6027，Cache Handle pin \u4f4f\u7684\u662f\u4e00\u4e2a\u7f13\u5b58\u5757\u7684\u53ef\u6dd8\u6c70\u6027\u3002\u00a0\u90fd\u662f\u201c\u4f60\u501f\u4e86\u4e00\u4e2a\u5f15\u7528，\u5c31\u5ef6\u957f\u4e86\u67d0\u4e2a\u4e1c\u897f\u8be5\u6b7b\u800c\u672a\u6b7b\u7684\u65f6\u95f4\u201d\u3002\u5b58\u50a8\u5f15\u64ce\u7684\u751f\u547d\u5468\u671f\u7ba1\u7406，\u4ece\u5e93\u3001\u5230\u5feb\u7167\u3001\u5230\u5217\u65cf\u53e5\u67c4\u3001\u5230\u4e00\u4e2a\u00a0PinnableSlice，\u4ece\u5934\u5230\u5c3e\u662f\u540c\u4e00\u5957\u54f2\u5b66\u5728\u4e0d\u540c\u7c92\u5ea6\u4e0a\u7684\u91cd\u590d：\u6bcf\u4e00\u4e2a\u53e5\u67c4，\u7ba1\u7684\u90fd\u662f\u53ef\u89c1\u6027 \/ \u53ef\u56de\u6536\u6027，\u4e0d\u662f\u5b58\u5728\u6027；\u4f60\u591a\u6525\u4e00\u4e2a\u5f15\u7528，\u5c31\u591a\u9489\u4f4f\u4e00\u5206\u672c\u8be5\u88ab\u56de\u6536\u7684\u8d44\u6e90\u3002<\/p>\n

          \u628a\u8fd9\u6761\u7ebf\u5728\u7f13\u5b58\u8fd9\u5934\u518d\u9489\u5b9e\u4e00\u70b9，\u56e0\u4e3a\u5b83\u76f4\u63a5\u5c31\u662f\u4f60\u8981\u8bbe\u8ba1\u7684\u7f13\u5b58\u7b56\u7565\u3002\u8bfb\u7f13\u5b58\u901a\u5e38\u662f\u4e2a LRU：\u5bb9\u91cf\u6ee1\u4e86，\u5c31\u628a\u6700\u4e45\u6ca1\u78b0\u7684\u5757\u8e22\u51fa\u53bb\u3002\u4f46\u201c\u8e22\u51fa\u53bb\u201d\u6709\u4e2a\u524d\u63d0\u2014\u2014\u8fd9\u4e2a\u5757\u6ca1\u88ab\u4efb\u4f55\u4eba pin \u4f4f\u3002\u4e00\u4e2a\u5757\u53ea\u8981\u8fd8\u6709\u4e00\u4e2a Cache Handle \u6ca1\u91ca\u653e，\u5b83\u7684\u5f15\u7528\u8ba1\u6570\u5c31\u4e0d\u4e3a\u96f6，LRU \u518d\u60f3\u6dd8\u6c70\u5b83\u4e5f\u53ea\u80fd\u8df3\u8fc7\u3002\u4e8e\u662f\u7f13\u5b58\u7684\u771f\u5b9e\u53ef\u7528\u5bb9\u91cf，\u662f\u201c\u603b\u5bb9\u91cf\u51cf\u53bb\u5f53\u524d\u88ab pin \u4f4f\u7684\u90a3\u90e8\u5206\u201d\u3002\u6b63\u5e38\u60c5\u51b5\u4e0b pin \u662f\u77ac\u65f6\u7684\u2014\u2014Get\u00a0\u62ff\u5230\u503c\u3001\u62f7\u8d70\u6216\u7528\u5b8c\u3001Reset，\u51e0\u5fae\u79d2\u7684\u4e8b，\u5bf9\u7f13\u5b58\u6beb\u65e0\u538b\u529b\u3002\u53ef\u53ea\u8981\u4f60\u628a\u4e00\u6279\u00a0PinnableSlice\u00a0\u6525\u5728\u624b\u91cc\u8fdf\u8fdf\u4e0d\u00a0Reset（\u6bd4\u5982\u628a\u4e00\u5806\u67e5\u8be2\u7ed3\u679c\u5bf9\u8c61\u7f13\u5b58\u8d77\u6765，\u6bcf\u4e2a\u91cc\u9762\u8eba\u7740\u4e00\u4e2a\u6ca1\u91ca\u653e\u7684\u00a0PinnableSlice），\u4f60\u5c31\u7b49\u4e8e\u5728\u7f13\u5b58\u91cc\u51ff\u4e86\u4e00\u6279\u6c38\u4e0d\u878d\u5316\u7684\u51b0\u5757，\u53ef\u7528\u5bb9\u91cf\u88ab\u6084\u6084\u5403\u6389，\u547d\u4e2d\u7387\u5f80\u4e0b\u6389\u2014\u2014\u800c\u4e14\u8fd9\u79cd\u4e0b\u8dcc\u5728\u76d1\u63a7\u4e0a\u6781\u96be\u5b9a\u4f4d：\u7f13\u5b58\u660e\u660e\u6ca1\u6ee1，\u547d\u4e2d\u7387\u5374\u5728\u5d29\u3002\u4f60\u81ea\u7814\u5f15\u64ce\u8bbe\u8ba1\u7f13\u5b58\u65f6，\u201c\u88ab pin \u4f4f\u7684\u5757\u4e0d\u8ba1\u5165\u53ef\u6dd8\u6c70\u5bb9\u91cf\u201d\u8fd9\u6761\u5fc5\u987b\u4e00\u5f00\u59cb\u5c31\u60f3\u6e05\u695a，\u5e76\u4e14\u7ed9\u201c\u957f\u671f\u88ab pin \u7684\u5757\u6570\u201d\u914d\u4e00\u4e2a\u6307\u6807，\u5426\u5219\u96f6\u62f7\u8d1d\u90a3\u70b9\u4fbf\u5229，\u8fdf\u65e9\u53d8\u6210\u4e00\u6b21\u8bf4\u4e0d\u6e05\u6839\u56e0\u7684\u6027\u80fd\u4e8b\u6545\u3002<\/p>\n

          \u6700\u540e\u8865\u4e00\u4e2a\u904d\u5386\u91cc\u5fc5\u8e29\u7684\u6536\u5c3e\u5751，\u628a\u751f\u547d\u5468\u671f\u548c\u9519\u8bef\u5904\u7406\u8fd9\u4e24\u6761\u7ebf\u5728\u8fd9\u91cc\u7cfb\u4e0a\u3002\u904d\u5386\u7ed3\u675f\u522b\u53ea\u770b\u00a0Valid()：<\/p>\n

          C++<\/p>\n

          for (it->SeekToFirst(); it->Valid(); it->Next()) {
          \n \/\/ \u5904\u7406 it->key(), it->value()
          \n}
          \nif (!it->status().ok()) {
          \n \/\/ Valid() \u53d8 false \u6709\u4e24\u79cd\u53ef\u80fd：\u8d70\u5230\u5934\u4e86，\u6216\u8005\u4e2d\u9014 IO \u51fa\u9519\u4e86！
          \n \/\/ \u53ea\u6709\u67e5 status() \u624d\u5206\u5f97\u6e05\u662f\u6b63\u5e38\u7ed3\u675f\u8fd8\u662f\u51fa\u9519\u4e2d\u65ad
          \n}<\/p>\n

          Valid()\u00a0\u8fd4\u56de false \u6709\u4e24\u79cd\u542b\u4e49：\u6b63\u5e38\u8d70\u5230\u4e86\u533a\u95f4\u5c3d\u5934，\u6216\u8005\u4e2d\u9014\u8bfb\u76d8\u51fa\u4e86\u9519\u3002iterator_base.h \u8bf4\u5f97\u5f88\u76f4\u767d\u2014\u2014Always returns false if !status().ok()\u3002\u8981\u662f\u4f60\u53ea\u7528\u00a0Valid()\u00a0\u5f53\u5faa\u73af\u6761\u4ef6\u3001\u4e0d\u5728\u5faa\u73af\u5916\u67e5\u4e00\u6b21\u00a0status()，\u4e00\u6b21\u8bfb\u76d8\u9519\u8bef\u5c31\u4f1a\u88ab\u4f60\u5f53\u6210\u201c\u6b63\u5e38\u904d\u5386\u5b8c\u4e86\u201d，\u6084\u6084\u6f0f\u6389\u534a\u4e2a\u533a\u95f4\u7684\u6570\u636e\u8fd8\u6d51\u7136\u4e0d\u89c9\u3002\u8fd9\u6b63\u597d\u547c\u5e94\u7b2c 7 \u8282：\u9519\u8bef\u662f\u4e00\u4e2a\u5fc5\u987b\u4e3b\u52a8\u53bb\u67e5\u7684\u8fd4\u56de\u503c，\u8fde\u8fed\u4ee3\u5668\u8fd9\u79cd\u5730\u65b9\u90fd\u4e0d\u4f8b\u5916\u3002<\/p>\n

          12. \u4e09\u9053\u5224\u65ad\u9898，\u628a\u8fd9\u5957\u6a21\u578b\u642c\u5230\u4f60\u81ea\u5df1\u7684\u5f15\u64ce\u4e0a<\/h3>\n

          \u56de\u5230\u5f00\u5934\u90a3\u4e5d\u884c\u4ee3\u7801\u3002\u90a3\u65f6\u4f60\u770b\u5230\u00a01 10 11 12 2\u00a0\u4f1a\u6123\u4e00\u4e0b，\u73b0\u5728\u4f60\u8be5\u80fd\u4e00\u53e3\u6c14\u8bf4\u6e05：\u5b83\u6309\u65e0\u7b26\u53f7\u5b57\u8282\u505a\u5b57\u5178\u5e8f（\u7b2c 3 \u8282），\u5b57\u7b26\u4e32\u00a0"12"\u00a0\u7684\u9996\u5b57\u8282\u6bd4\u00a0"2"\u00a0\u5c0f；\u8981\u8ba9\u5b83\u6309\u6570\u503c\u6392，key \u91cc\u7684\u6574\u6570\u5f97\u5927\u7aef\u7f16\u7801\u3002\u540c\u4e00\u6bb5\u4ee3\u7801，\u4f60\u624b\u91cc\u7684\u4fe1\u606f\u5df2\u7ecf\u5b8c\u5168\u4e0d\u540c\u4e86\u3002<\/p>\n

          \u4e0d\u505a\u603b\u7ed3，\u7ed9\u4f60\u4e09\u9053\u5224\u65ad\u9898，\u6bcf\u9053\u90fd\u5bf9\u7740\u4f60\u81ea\u7814\u5f15\u64ce\u65f6\u771f\u4f1a\u4e0b\u7684\u4e00\u4e2a\u51b3\u5b9a，\u968f\u5224\u968f\u7b54：<\/p>\n

          \u7b2c\u4e00\u9898：\u4f60\u7684 key \u7f16\u7801，\u5728\u5b57\u8282\u5b57\u5178\u5e8f\u4e0b\u987a\u5e8f\u8fd8\u5bf9\u5417？\u00a0\u4f46\u51e1\u4f60\u7684\u5f15\u64ce\u8981\u652f\u6301\u8303\u56f4\u626b\u63cf，\u8fd9\u5c31\u662f\u7b2c\u4e00\u9053\u574e\u3002\u6574\u6570\u4e3b\u952e？\u5fc5\u987b\u5927\u7aef\u3002\u591a\u5b57\u6bb5\u590d\u5408 key？\u6bcf\u4e2a\u5b57\u6bb5\u7684\u8fb9\u754c\u548c\u987a\u5e8f\u90fd\u5f97\u5728\u5b57\u8282\u5c42\u9762\u5bf9\u9f50\u3002\u5b9a\u957f\u8fd8\u662f\u53d8\u957f，\u76f4\u63a5\u51b3\u5b9a\u524d\u7f00\u626b\u63cf\u6210\u4e0d\u6210\u7acb\u3002\u7b54\u4e0d\u5229\u7d22\u8fd9\u4e00\u9898，\u4f60\u7684\u6709\u5e8f\u6027\u662f\u5047\u7684\u2014\u2014\u4e0d\u62a5\u9519，\u53ea\u662f\u626b\u63cf\u7ed3\u679c\u6084\u6084\u4e0d\u5bf9\u3002<\/p>\n

          \u7b2c\u4e8c\u9898：\u4f60\u8fd9\u5957\u63a5\u53e3\u91cc，\u54ea\u4e9b\u5bf9\u8c61 pin \u7684\u662f\u201c\u53ef\u89c1\u6027\u201d，\u54ea\u4e9b\u662f\u201c\u5b58\u5728\u6027\u201d？\u00a0\u5feb\u7167\u3001\u5217\u65cf\u53e5\u67c4\u3001PinnableSlice\u3001\u8fed\u4ee3\u5668，\u5168\u662f\u5f15\u7528\u578b\u5bf9\u8c61，\u5b83\u4eec\u9489\u4f4f\u7684\u90fd\u662f\u201c\u53ef\u56de\u6536\u6027\u201d\u8fd9\u6839\u8f74，\u4e0d\u662f\u201c\u5b58\u5728\u6027\u201d\u3002\u60f3\u6e05\u695a\u6bcf\u4e00\u4e2a\u7684\u91ca\u653e\u4f1a\u653e\u5f00\u4ec0\u4e48\u3001\u5fd8\u4e86\u91ca\u653e\u4f1a\u9489\u4f4f\u4ec0\u4e48\u2014\u2014\u5173\u4e0d\u6389\u7684\u5e93\u3001\u6dd8\u6c70\u4e0d\u6389\u7684\u7f13\u5b58\u5757\u3001\u56de\u6536\u4e0d\u4e86\u7684\u65e7\u7248\u672c，\u6839\u5b50\u90fd\u5728\u8fd9\u91cc\u3002\u7ed9\u6bcf\u4e2a\u8fd9\u6837\u7684\u5f15\u7528\u914d\u4e00\u4e2a RAII \u5305\u88c5，\u628a\u6210\u5bf9\u8c03\u7528\u7684\u7eaa\u5f8b\u4ece\u8c03\u7528\u65b9\u7684\u8bb0\u6027\u91cc\u62ff\u8d70\u3002<\/p>\n

          \u7b2c\u4e09\u9898：\u4f60\u7684\u9519\u8bef\u901a\u9053，\u662f\u503c\u8fd8\u662f\u5f02\u5e38？\u00a0\u5982\u679c\u4f60\u7684\u5f15\u64ce\u6838\u5fc3\u4e5f\u78b0\u78c1\u76d8\u3001\u4e5f\u5e26\u5e76\u53d1\u3001\u4e5f\u5bb9\u4e0d\u4e0b\u201c\u534a\u4e2a\u64cd\u4f5c\u201d，\u8ba4\u771f\u8003\u8651\u8d70\u8fd4\u56de\u503c\u00a0Status\u3002\u4f46\u5149\u6709\u8fd4\u56de\u503c\u4e0d\u591f\u2014\u2014\u914d\u4e00\u5957\u80fd\u5728\u6d4b\u8bd5\u6784\u5efa\u91cc\u628a\u201c\u6f0f\u68c0\u8fd4\u56de\u503c\u201d\u53d8\u6210\u5f53\u573a\u5d29\u6e83\u7684\u673a\u5236，\u5426\u5219\u5b83\u8fdf\u65e9\u9000\u5316\u6210\u6bd4\u5f02\u5e38\u66f4\u5371\u9669\u7684\u4e1c\u897f：\u88ab\u65e0\u58f0\u541e\u6389\u7684\u9519\u8bef\u3002<\/p>\n

          \u4e09\u9053\u9898\u80cc\u540e\u662f\u540c\u4e00\u53e5\u5224\u65ad，\u4e5f\u662f\u8fd9\u7bc7\u552f\u4e00\u60f3\u710a\u8fdb\u4f60\u8111\u5b50\u7684\u90a3\u4e00\u53e5：\u6709\u5e8f KV \u5b58\u50a8\u7684\u6bcf\u4e00\u4e2a\u63a5\u53e3\u51b3\u5b9a，\u6700\u7ec8\u90fd\u6536\u655b\u5230\u4e00\u4e2a\u95ee\u9898\u2014\u2014\u987a\u5e8f\u7531\u8c01\u5b9a\u4e49\u3001\u72b6\u6001\u5bf9\u8c01\u53ef\u89c1\u3001\u8d44\u6e90\u5f52\u8c01\u56de\u6536\u3002\u00a0\u987a\u5e8f\u5373\u8eab\u4efd，\u53ef\u89c1\u5373\u7248\u672c，\u5f15\u7528\u5373\u8d26\u5355\u3002\u4f60\u628a\u81ea\u7814\u5f15\u64ce\u7684\u63a5\u53e3\u6309\u8fd9\u4e09\u6761\u634b\u4e00\u904d，\u78c1\u76d8 IO\u3001\u7f13\u5b58\u7b56\u7565\u3001\u6027\u80fd\u4f18\u5316\u90a3\u4e9b\u4e0b\u6e38\u7684\u6d3b，\u624d\u6709\u4e00\u4e2a\u7acb\u5f97\u4f4f\u7684\u5730\u57fa\u3002<\/p>\n

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