{"id":2991,"date":"2019-03-28T17:20:00","date_gmt":"2019-03-28T09:20:00","guid":{"rendered":"https:\/\/damogame.cn:15443\/wordpress\/?p=2991"},"modified":"2019-03-28T17:20:55","modified_gmt":"2019-03-28T09:20:55","slug":"%e5%8d%8a%e5%b0%8f%e6%97%b6%e5%ad%a6%e4%bc%9aleveldb%e5%8e%9f%e7%90%86%e5%8f%8a%e5%ba%94%e7%94%a8","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/2991","title":{"rendered":"\u534a\u5c0f\u65f6\u5b66\u4f1aLevelDB\u539f\u7406\u53ca\u5e94\u7528"},"content":{"rendered":"<div class=\"article-header-box\">\n<div class=\"article-header\"><\/div>\n<\/div>\n<article class=\"baidu_pl\">\n<div id=\"article_content\" class=\"article_content clearfix csdn-tracking-statistics\" data-pid=\"blog\" data-mod=\"popu_307\" data-dsm=\"post\">\n<div id=\"content_views\" class=\"markdown_views\">\n<p>LevelDB\u662fGoogle\u4f20\u5947\u5de5\u7a0b\u5e08<a href=\"https:\/\/research.google.com\/pubs\/jeff.html\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">Jeff Dean<\/a>\u548c<a href=\"https:\/\/research.google.com\/pubs\/SanjayGhemawat.html\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">Sanjay Ghemawat<\/a>\u5f00\u6e90\u7684KV\u5b58\u50a8\u5f15\u64ce\u3002<br \/>\n\u4e86\u89e3\u539f\u7406\u4e4b\u524d\u9996\u5148\u8981\u7528\u8d77\u6765\uff0c\u4e0b\u9762\u52a8\u624b\u5b9e\u73b0\u4e2a\u4f8b\u5b50\uff1a<a href=\"https:\/\/github.com\/google\/leveldb\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">\u5b89\u88c5\u8c03\u8bd5<\/a>(mac\u4e0a\u76f4\u63a5\u547d\u4ee4\u884c\u4e0b<a href=\"https:\/\/brew.sh\/\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">brew<\/a>\u00a0install leveldb\u5373\u53ef\u5b89\u88c5\uff0c\u7f16\u8bd1\u65f6\u5019\u8bb0\u5f97\u52a0\u4e0a-lleveldb)<br \/>\nexample:<\/p>\n<\/div>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"null\">#include &lt;assert.h&gt;\r\n#include &lt;string.h&gt;\r\n#include &lt;leveldb\/db.h&gt;\r\n#include &lt;iostream&gt;\r\n\r\nint main(int argc, char** argv)\r\n{\r\n    leveldb::DB* db;\r\n    leveldb::Options options;\r\n    \/\/ \u5982\u679c\u6253\u5f00\u5df2\u5b58\u5728\u6570\u636e\u5e93\u7684\u65f6\u5019\uff0c\u9700\u8981\u629b\u51fa\u9519\u8bef\uff0c\u5c06\u4ee5\u4e0b\u4ee3\u7801\u63d2\u5728leveldb::DB::Open\u65b9\u6cd5\u524d\u9762\r\n    options.create_if_missing = true;\r\n    \/\/ \u6253\u5f00\u4e00\u4e2a\u6570\u636e\u5e93\u5b9e\u4f8b\r\n    leveldb::Status status = leveldb::DB::Open(options, \"\/tmp\/testdb\", &amp;db);\r\n    assert(status.ok());\r\n    \/\/ LevelDB\u63d0\u4f9b\u4e86Put\u3001Get\u548cDelete\u4e09\u4e2a\u65b9\u6cd5\u5bf9\u6570\u636e\u5e93\u8fdb\u884c\u6dfb\u52a0\u3001\u67e5\u8be2\u548c\u5220\u9664\r\n    std::string key = \"key\";\r\n    std::string value = \"value\";\r\n    \/\/ \u6dfb\u52a0key=value\r\n    status = db-&gt;Put(leveldb::WriteOptions(), key, value);\r\n    assert(status.ok());\r\n    \/\/ \u6839\u636ekey\u67e5\u8be2value\r\n    status = db-&gt;Get(leveldb::ReadOptions(), key, &amp;value);\r\n    assert(status.ok());\r\n    std::cout&lt;&lt;value&lt;&lt;std::endl;\r\n    \/\/ \u4fee\u6539\u64cd\u4f5c\uff08\u539f\u751f\u6ca1\u6709\u63d0\u4f9b\uff09\u7531\u6dfb\u52a0\u548c\u5220\u9664\u5408\u8d77\u6765\u5b9e\u73b0\r\n    std::string key2 = \"key2\";\r\n    \/\/ \u6dfb\u52a0key2=value\r\n    status = db-&gt;Put(leveldb::WriteOptions(),key2,value);\r\n    assert(status.ok());\r\n    \/\/ \u5220\u9664key\r\n    status = db-&gt;Delete(leveldb::WriteOptions(), key);\r\n    \/\/ \u67e5\u8be2key2\r\n    assert(status.ok());\r\n    status = db-&gt;Get(leveldb::ReadOptions(), key2, &amp;value);\r\n    assert(status.ok());\r\n    std::cout&lt;&lt;key2&lt;&lt;\"==\"&lt;&lt;value&lt;&lt;std::endl;\r\n    \/\/ \u67e5\u8be2key\r\n    status = db-&gt;Get(leveldb::ReadOptions(), key, &amp;value);\r\n    if (!status.ok()) {\r\n        std::cerr &lt;&lt; key &lt;&lt; \": \" &lt;&lt; status.ToString() &lt;&lt; std::endl;\r\n    } else {\r\n        std::cout &lt;&lt; key &lt;&lt; \"==\" &lt;&lt; value &lt;&lt; std::endl;\r\n    }\r\n    delete db;\r\n    return 0;\r\n}<\/pre>\n<div id=\"content_views\" class=\"markdown_views\">\n<h2 id=\"\u8bbe\u8ba1\u601d\u8def\">\u8bbe\u8ba1\u601d\u8def<\/h2>\n<p>LevelDB\u7684\u6570\u636e\u662f\u5b58\u50a8\u5728\u78c1\u76d8\u4e0a\u7684\uff0c\u91c7\u7528<a href=\"http:\/\/ov6v82oa9.bkt.clouddn.com\/download.pdf\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">LSM-Tree<\/a>\u7684\u7ed3\u6784\u5b9e\u73b0\u3002LSM-Tree\u5c06\u78c1\u76d8\u7684\u968f\u673a\u5199\u8f6c\u5316\u4e3a\u987a\u5e8f\u5199\uff0c\u4ece\u800c\u5927\u5927\u63d0\u9ad8\u4e86\u5199\u901f\u5ea6\u3002<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/9092b78b-5c7a-37df-b9f2-fb8038bb79b9.jpg\" alt=\"1\" \/><br \/>\n\u4e3a\u4e86\u505a\u5230\u8fd9\u4e00\u70b9LSM-Tree\u7684\u601d\u8def\u662f\u5c06\u7d22\u5f15\u6811\u7ed3\u6784\u62c6\u6210\u4e00\u5927\u4e00\u5c0f\u4e24\u9897\u6811\uff0c\u8f83\u5c0f\u7684\u4e00\u4e2a\u5e38\u9a7b\u5185\u5b58\uff0c\u8f83\u5927\u7684\u4e00\u4e2a\u6301\u4e45\u5316\u5230\u78c1\u76d8\uff0c\u4ed6\u4eec\u5171\u540c\u7ef4\u62a4\u4e00\u4e2a\u6709\u5e8f\u7684key\u7a7a\u95f4\u3002<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/7ece3749-415a-3083-893e-6859c9b9fc78.jpg\" alt=\"2\" \/><br \/>\n\u5199\u5165\u64cd\u4f5c\u4f1a\u9996\u5148\u64cd\u4f5c\u5185\u5b58\u4e2d\u7684\u6811\uff0c\u968f\u7740\u5185\u5b58\u4e2d\u6811\u7684\u4e0d\u65ad\u53d8\u5927\uff0c\u4f1a\u89e6\u53d1\u4e0e\u78c1\u76d8\u4e2d\u6811\u7684\u5f52\u5e76\u64cd\u4f5c\uff0c\u800c\u5f52\u5e76\u64cd\u4f5c\u672c\u8eab\u4ec5\u6709\u987a\u5e8f\u5199\u3002\u968f\u7740\u6570\u636e\u7684\u4e0d\u65ad\u5199\u5165\uff0c\u78c1\u76d8\u4e2d\u7684\u6811\u4f1a\u4e0d\u65ad\u81a8\u80c0\uff0c\u4e3a\u4e86\u907f\u514d\u6bcf\u6b21\u53c2\u4e0e\u5f52\u5e76\u64cd\u4f5c\u7684\u6570\u636e\u91cf\u8fc7\u5927\uff0c\u4ee5\u53ca\u4f18\u5316\u8bfb\u64cd\u4f5c\u7684\u8003\u8651\uff0cLevelDB\u5c06\u78c1\u76d8\u4e2d\u7684\u6570\u636e\u53c8\u62c6\u5206\u6210\u591a\u5c42\uff0c\u6bcf\u4e00\u5c42\u7684\u6570\u636e\u8fbe\u5230\u4e00\u5b9a\u5bb9\u91cf\u540e\u4f1a\u89e6\u53d1\u5411\u4e0b\u4e00\u5c42\u7684\u5f52\u5e76\u64cd\u4f5c\uff0c\u6bcf\u4e00\u5c42\u7684\u6570\u636e\u91cf\u6bd4\u5176\u4e0a\u4e00\u5c42\u6210\u500d\u589e\u957f\u3002\u8fd9\u4e5f\u5c31\u662fLevelDB\u7684\u540d\u79f0\u6765\u6e90\u3002<\/p>\n<h2 id=\"\u6574\u4f53\u7ed3\u6784\">\u6574\u4f53\u7ed3\u6784<\/h2>\n<p>\u5185\u5b58\u6570\u636e\u7684Memtable\uff0c\u5206\u5c42\u6570\u636e\u5b58\u50a8\u7684SST\u6587\u4ef6\uff0c\u7248\u672c\u63a7\u5236\u7684Manifest\u3001Current\u6587\u4ef6\uff0c\u4ee5\u53ca\u5199Memtable\u524d\u7684WAL\u3002<\/p>\n<p>WAL:\u00a0<code>Write-Ahead Logging<\/code>\u9884\u5199\u65e5\u5fd7\u7cfb\u7edf<br \/>\n\u6570\u636e\u5e93\u4e2d\u4e00\u79cd\u9ad8\u6548\u7684\u65e5\u5fd7\u7b97\u6cd5\uff0c\u5bf9\u4e8e\u975e\u5185\u5b58\u6570\u636e\u5e93\u800c\u8a00\uff0c\u78c1\u76d8I\/O\u64cd\u4f5c\u662f\u6570\u636e\u5e93\u6548\u7387\u7684\u4e00\u5927\u74f6\u9888\u3002\u5728\u76f8\u540c\u7684\u6570\u636e\u91cf\u4e0b\uff0c\u91c7\u7528WAL\u65e5\u5fd7\u7684\u6570\u636e\u5e93\u7cfb\u7edf\u5728\u4e8b\u52a1\u63d0\u4ea4\u65f6\uff0c\u78c1\u76d8\u5199\u64cd\u4f5c\u53ea\u6709\u4f20\u7edf\u7684\u56de\u6eda\u65e5\u5fd7\u7684\u4e00\u534a\u5de6\u53f3\uff0c\u5927\u5927\u63d0\u9ad8\u4e86\u6570\u636e\u5e93\u78c1\u76d8I\/O\u64cd\u4f5c\u7684\u6548\u7387\uff0c\u4ece\u800c\u63d0\u9ad8\u4e86\u6570\u636e\u5e93\u7684\u6027\u80fd\u3002<\/p>\n<p><img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/15037067311885.jpg\" alt=\"\" \/><br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/0_1487308288666_TB1FFIRPpXXXXa9XVXXXXXXXXXX.png.png\" alt=\"\u6574\u4f53\u7ed3\u6784.png\" \/><\/p>\n<h3 id=\"memtable\">Memtable\uff1a<\/h3>\n<p>\u5bf9\u5e94Leveldb\u4e2d\u7684\u5185\u5b58\u6570\u636e\uff0cLevelDB\u7684\u5199\u5165\u64cd\u4f5c\u4f1a\u76f4\u63a5\u5c06\u6570\u636e\u5199\u5165\u5230Memtable\u540e\u8fd4\u56de\u3002\u8bfb\u53d6\u64cd\u4f5c\u53c8\u4f1a\u9996\u5148\u5c1d\u8bd5\u4eceMemtable\u4e2d\u8fdb\u884c\u67e5\u8be2\uff0c\u5141\u8bb8\u5199\u5165\u548c\u8bfb\u53d6\u3002\u5f53Memtable\u5199\u5165\u7684\u6570\u636e\u5360\u7528\u5185\u5b58\u5230\u8fbe\u6307\u5b9a\u6570\u91cf\uff0c\u5219\u81ea\u52a8\u8f6c\u6362\u4e3aImmutable Memtable\uff0c\u7b49\u5f85Dump\u5230\u78c1\u76d8\u4e2d\uff0c\u7cfb\u7edf\u4f1a\u81ea\u52a8\u751f\u6210\u65b0\u7684Memtable\u4f9b\u5199\u64cd\u4f5c\u5199\u5165\u65b0\u6570\u636e\u3002<br \/>\nLevelDB\u91c7\u7528\u8df3\u8868SkipList\u5b9e\u73b0\uff0c\u5728\u7ed9\u63d0\u4f9b\u4e86O(logn)\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u7684\u540c\u65f6\uff0c\u53c8\u975e\u5e38\u7684\u6613\u4e8e\u5b9e\u73b0\uff1a<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/0_1501291738687_5a9caa85-bfbb-4be0-9dc0-50c4474078f3-image.png.png\" alt=\"SkipList\" \/><br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/15037076645668.jpg\" alt=\"SkipList\" \/><\/p>\n<p>\u8df3\u8868\u4f5c\u4e3a\u4e00\u79cd\u6570\u636e\u7ed3\u6784\u901a\u5e38\u7528\u4e8e\u53d6\u4ee3\u5e73\u8861\u6811\uff0c\u4e0e\u7ea2\u9ed1\u6811\u4e0d\u540c\u7684\u662f\uff0c<a href=\"http:\/\/ov6v82oa9.bkt.clouddn.com\/skiplist.pdf\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">skiplist<\/a>\u5bf9\u4e8e\u6811\u7684\u5e73\u8861\u7684\u5b9e\u73b0\u662f\u57fa\u4e8e\u4e00\u79cd\u968f\u673a\u5316\u7684\u7b97\u6cd5\u7684\uff0c\u4e5f\u5c31\u662f\u8bf4skiplist\u7684\u63d2\u5165\u548c\u5220\u9664\u7684\u5de5\u4f5c\u662f\u6bd4\u8f83\u7b80\u5355\u5730\u3002<\/p>\n<p>SkipList\u4e2d\u5355\u6761\u6570\u636e\u5b58\u653e\u4e00\u6761Key-Value\u6570\u636e\uff0c\u5b9a\u4e49\u4e3a\uff1a<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"null\">SkipList Node := InternalKey + ValueString\r\nInternalKey := KeyString + SequenceNum + Type\r\nType := kDelete or kValue\r\nValueString := ValueLength + Value\r\nKeyString := UserKeyLength + UserKey<\/pre>\n<h3 id=\"log\u6587\u4ef6\">Log\u6587\u4ef6<\/h3>\n<p>\u5f53\u5e94\u7528\u5199\u5165\u4e00\u6761Key:Value\u8bb0\u5f55\u7684\u65f6\u5019\uff0cLevelDb\u4f1a\u5148\u5f80log\u6587\u4ef6\u91cc\u5199\u5165\uff0c\u6210\u529f\u540e\u5c06\u8bb0\u5f55\u63d2\u8fdbMemtable\u4e2d\uff0c\u8fd9\u6837\u57fa\u672c\u5c31\u7b97\u5b8c\u6210\u4e86\u5199\u5165\u64cd\u4f5c\uff0cLog\u6587\u4ef6\u5728\u7cfb\u7edf\u4e2d\u7684\u4f5c\u7528\u4e3b\u8981\u662f\u7528\u4e8e\u7cfb\u7edf\u5d29\u6e83\u6062\u590d\u800c\u4e0d\u4e22\u5931\u6570\u636e\uff0c\u5047\u5982\u6ca1\u6709Log\u6587\u4ef6\uff0c\u56e0\u4e3a\u5199\u5165\u7684\u8bb0\u5f55\u521a\u5f00\u59cb\u662f\u4fdd\u5b58\u5728\u5185\u5b58\u4e2d\u7684\uff0c\u6b64\u65f6\u5982\u679c\u7cfb\u7edf\u5d29\u6e83\uff0c\u5185\u5b58\u4e2d\u7684\u6570\u636e\u8fd8\u6ca1\u6709\u6765\u5f97\u53caDump\u5230\u78c1\u76d8\uff0c\u6240\u4ee5\u4f1a\u4e22\u5931\u6570\u636e\uff08Redis\u5c31\u5b58\u5728\u8fd9\u4e2a\u95ee\u9898\uff09\u3002<br \/>\n\u56e0\u4e3a\u4e00\u6b21\u5199\u5165\u64cd\u4f5c\u53ea\u6d89\u53ca\u4e00\u6b21\u78c1\u76d8\u987a\u5e8f\u5199\u548c\u4e00\u6b21\u5185\u5b58\u5199\u5165\uff0c\u6240\u4ee5\u8fd9\u662f\u4e3a\u4f55\u8bf4LevelDb\u5199\u5165\u901f\u5ea6\u6781\u5feb\u7684\u4e3b\u8981\u539f\u56e0\u3002<br \/>\nLevelDB\u9996\u5148\u5c06\u6bcf\u6761\u5199\u5165\u6570\u636e\u5e8f\u5217\u5316\u4e3a\u4e00\u4e2aRecord\uff0c\u5355\u4e2aLog\u6587\u4ef6\u4e2d\u5305\u542b\u591a\u4e2aRecord\u3002\u540c\u65f6\uff0cLog\u6587\u4ef6\u53c8\u5212\u5206\u4e3a\u56fa\u5b9a\u5927\u5c0f\u7684Block\u5355\u4f4d\uff0c\u5e76\u4fdd\u8bc1Block\u7684\u5f00\u59cb\u4f4d\u7f6e\u4e00\u5b9a\u662f\u4e00\u4e2a\u65b0\u7684Record\u3002\u8fd9\u79cd\u5b89\u6392\u4f7f\u5f97\u53d1\u751f\u6570\u636e\u9519\u8bef\u65f6\uff0c\u6700\u591a\u53ea\u9700\u4e22\u5f03\u4e00\u4e2aBlock\u5927\u5c0f\u7684\u5185\u5bb9\u3002\u663e\u800c\u6613\u89c1\u5730\uff0c\u4e0d\u540c\u7684Record\u53ef\u80fd\u5171\u5b58\u4e8e\u4e00\u4e2aBlock\uff0c\u540c\u65f6\uff0c\u4e00\u4e2aRecord\u4e5f\u53ef\u80fd\u6a2a\u8de8\u51e0\u4e2aBlock\u3002<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb-log.png\" alt=\"leveldb-log\" \/><br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/15037110902017.jpg\" alt=\"\" \/><br \/>\nLog\u6587\u4ef6\u5212\u5206\u4e3a\u56fa\u5b9a\u957f\u5ea6\u7684Block\uff0c\u7531\u8fde\u7eed\u768432K\u4e3a\u5355\u4f4d\u7684\u7269\u7406Block\u6784\u6210\u7684\uff0c\u6bcf\u6b21\u8bfb\u53d6\u7684\u5355\u4f4d\u662f\u4ee5\u4e00\u4e2aBlock\u4f5c\u4e3a\u57fa\u672c\u5355\u4f4d\uff1b\u6bcf\u4e2aBlock\u4e2d\u5305\u542b\u591a\u4e2aRecord\uff1bRecord\u7684\u524d56\u4e2a\u4f4d\u4e3aRecord\u5934\uff0c\u5305\u62ec32\u4f4dchecksum\u7528\u505a\u6821\u9a8c\uff0c16\u4f4d\u5b58\u50a8Record\u5b9e\u9645\u5185\u5bb9\u6570\u636e\u7684\u957f\u5ea6\uff0c8\u4f4d\u7684Type\u53ef\u4ee5\u662fFull\u3001First\u3001Middle\u6216Last\u4e2d\u7684\u4e00\u79cd\uff0c\u8868\u793a\u8be5Record\u662f\u5426\u5b8c\u6574\u7684\u5728\u5f53\u524d\u7684Block\u4e2d\uff0c\u5982\u679cType\u4e0d\u662fFull\uff0c\u5219\u901a\u8fc7Type\u6307\u660e\u5176\u524d\u540e\u7684Block\u4e2d\u662f\u5426\u6709\u5f53\u524dRecord\u7684\u524d\u9a71\u540e\u7ee7\u3002<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb-log2.png\" alt=\"leveldb-log2\" \/><\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"null\">Block := Record * N\r\nRecord := Header + Content\r\nHeader := Checksum + Length + Type\r\nType := Full or First or Midder or Last<\/pre>\n<h3 id=\"immutable-memtable\">Immutable Memtable<\/h3>\n<p>\u5f53Memtable\u63d2\u5165\u7684\u6570\u636e\u5360\u7528\u5185\u5b58\u5230\u4e86\u4e00\u4e2a\u754c\u9650\u540e\uff0c\u9700\u8981\u5c06\u5185\u5b58\u7684\u8bb0\u5f55\u5bfc\u51fa\u5230\u5916\u5b58\u6587\u4ef6\u4e2d\uff0cLevleDb\u4f1a\u751f\u6210\u65b0\u7684Log\u6587\u4ef6\u548cMemtable\uff0cMemtable\u4f1a\u53d8\u4e3aImmutable\uff0c\u4e3a\u4e4b\u540e\u5411SST\u6587\u4ef6\u7684\u5f52\u5e76\u505a\u51c6\u5907\u3002\u987e\u540d\u601d\u4e49\uff0cImmutable Mumtable\u4e0d\u518d\u63a5\u53d7\u7528\u6237\u5199\u5165\uff0c\u53ea\u80fd\u8bfb\u4e0d\u80fd\u5199\u5165\u6216\u8005\u5220\u9664\uff0c\u540c\u65f6\u4f1a\u6709\u65b0\u7684Log\u6587\u4ef6\u548cMemtable\u751f\u6210\uff0cLevelDb\u540e\u53f0\u8c03\u5ea6\u4f1a\u5c06Immutable Memtable\u7684\u6570\u636e\u5bfc\u51fa\u5230\u78c1\u76d8\uff0c\u5f62\u6210\u4e00\u4e2a\u65b0\u7684SSTable\u6587\u4ef6\u3002<\/p>\n<h3 id=\"sst\u6587\u4ef6\">SST\u6587\u4ef6<\/h3>\n<p>SSTable\u5c31\u662f\u7531\u5185\u5b58\u4e2d\u7684\u6570\u636e\u4e0d\u65ad\u5bfc\u51fa\u5e76\u8fdb\u884c<strong>Compaction<\/strong>\u64cd\u4f5c(\u538b\u7f29\u64cd\u4f5c\uff0c\u4e0b\u6587\u4f1a\u8bb2\u5230)\u540e\u5f62\u6210\u7684\uff0c\u800c\u4e14SSTable\u7684\u6240\u6709\u6587\u4ef6\u662f\u4e00\u79cd\u5c42\u7ea7\u7ed3\u6784\uff0c\u7b2c\u4e00\u5c42\u4e3aLevel 0\uff0c\u7b2c\u4e8c\u5c42\u4e3aLevel 1\uff0c\u4f9d\u6b21\u7c7b\u63a8\uff0c\u5c42\u7ea7\u9010\u6e10\u589e\u9ad8\uff0c\u8fd9\u4e5f\u662f\u4e3a\u4f55\u79f0\u4e4b\u4e3aLevelDb\u7684\u539f\u56e0\u3002<br \/>\n\u78c1\u76d8\u6570\u636e\u5b58\u50a8\u6587\u4ef6\u3002\u5206\u4e3a<code>Level 0<\/code>\u5230<code>Level N<\/code>\u591a\u5c42\uff0c\u6bcf\u4e00\u5c42\u5305\u542b\u591a\u4e2aSST\u6587\u4ef6\uff1b\u5355\u4e2aSST\u6587\u4ef6\u5bb9\u91cf\u968f\u5c42\u6b21\u589e\u52a0\u6210\u500d\u589e\u957f\uff1b\u6587\u4ef6\u5185\u6570\u636e\u6709\u5e8f\uff1b\u5176\u4e2d<code>Level 0<\/code>\u7684SST\u6587\u4ef6\u7531Immutable\u76f4\u63a5Dump\u4ea7\u751f\uff0c\u5176\u4ed6Level\u7684SST\u6587\u4ef6\u7531\u5176\u4e0a\u4e00\u5c42\u7684\u6587\u4ef6\u548c\u672c\u5c42\u6587\u4ef6\u5f52\u5e76\u4ea7\u751f\uff1bSST\u6587\u4ef6\u5728\u5f52\u5e76\u8fc7\u7a0b\u4e2d\u987a\u5e8f\u5199\u751f\u6210\uff0c\u751f\u6210\u540e\u4ec5\u53ef\u80fd\u5728\u4e4b\u540e\u7684\u5f52\u5e76\u4e2d\u88ab\u5220\u9664\uff0c\u800c\u4e0d\u4f1a\u6709\u4efb\u4f55\u7684\u4fee\u6539\u64cd\u4f5c\u3002<br \/>\nSSTable\u4e2d\u7684\u6587\u4ef6\u662fKey\u6709\u5e8f\u7684\uff0c\u5c31\u662f\u8bf4\u5728\u6587\u4ef6\u4e2d\u5c0fkey\u8bb0\u5f55\u6392\u5728\u5927Key\u8bb0\u5f55\u4e4b\u524d\uff0c\u5404\u4e2aLevel\u7684SSTable\u90fd\u662f\u5982\u6b64\uff0c\u4f46\u662f\u8fd9\u91cc\u9700\u8981\u6ce8\u610f\u7684\u4e00\u70b9\u662f\uff1aLevel 0\u7684SSTable\u6587\u4ef6\uff08\u540e\u7f00\u4e3a.sst\uff09\u548c\u5176\u5b83Level\u7684\u6587\u4ef6\u76f8\u6bd4\u6709\u7279\u6b8a\u6027\uff1a\u8fd9\u4e2a\u5c42\u7ea7\u5185\u7684.sst\u6587\u4ef6\uff0c\u4e24\u4e2a\u6587\u4ef6\u53ef\u80fd\u5b58\u5728key\u91cd\u53e0\uff0c\u6bd4\u5982\u6709\u4e24\u4e2alevel 0\u7684sst\u6587\u4ef6\uff0c\u6587\u4ef6A\u548c\u6587\u4ef6B\uff0c\u6587\u4ef6A\u7684key\u8303\u56f4\u662f\uff1a{bar, car}\uff0c\u6587\u4ef6B\u7684Key\u8303\u56f4\u662f{blue,samecity}:<\/p>\n<div class=\"table-box\">\n<table>\n<thead>\n<tr>\n<th>level N<\/th>\n<th>.sst<\/th>\n<th>max<\/th>\n<th>min<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Level 0<\/td>\n<td>A.sst<\/td>\n<td>\u201cbar\u201d<\/td>\n<td>\u201ccar\u201d<\/td>\n<\/tr>\n<tr>\n<td>Level 0<\/td>\n<td>B.sst<\/td>\n<td>\u201cblue\u201d<\/td>\n<td>\u201csamecity\u201d<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u90a3\u4e48\u5f88\u53ef\u80fd\u4e24\u4e2a\u6587\u4ef6\u90fd\u5b58\u5728key=\u201dblood\u201d\u7684\u8bb0\u5f55\u3002\u5bf9\u4e8e\u5176\u5b83Level\u7684SSTable\u6587\u4ef6\u6765\u8bf4\uff0c\u5219\u4e0d\u4f1a\u51fa\u73b0\u540c\u4e00\u5c42\u7ea7\u5185\u3002<\/p>\n<h4 id=\"sst\u6587\u4ef6\u7684\u7269\u7406\u683c\u5f0f\">SST\u6587\u4ef6\u7684\u7269\u7406\u683c\u5f0f<\/h4>\n<p>LevelDb\u4e0d\u540c\u5c42\u7ea7\u6709\u5f88\u591aSSTable\u6587\u4ef6\uff08\u4ee5\u540e\u7f00.sst\u4e3a\u7279\u5f81\uff09\uff0c\u6240\u6709.sst\u6587\u4ef6\u5185\u90e8\u5e03\u5c40\u90fd\u662f\u4e00\u6837\u7684\u3002\u4e0a\u8282\u4ecb\u7ecdLog\u6587\u4ef6\u662f\u7269\u7406\u5206\u5757\u7684\uff0cSSTable\u4e5f\u4e00\u6837\u4f1a\u5c06\u6587\u4ef6\u5212\u5206\u4e3a\u56fa\u5b9a\u5927\u5c0f\u7684\u7269\u7406\u5b58\u50a8\u5757\uff0c\u4f46\u662f\u4e24\u8005\u903b\u8f91\u5e03\u5c40\u5927\u4e0d\u76f8\u540c\uff0c\u6839\u672c\u539f\u56e0\u662f\uff1aLog\u6587\u4ef6\u4e2d\u7684\u8bb0\u5f55\u662fKey\u65e0\u5e8f\u7684\uff0c\u5373\u5148\u540e\u8bb0\u5f55\u7684key\u5927\u5c0f\u6ca1\u6709\u660e\u786e\u5927\u5c0f\u5173\u7cfb\uff0c\u800c.sst\u6587\u4ef6\u5185\u90e8\u5219\u662f\u6839\u636e\u8bb0\u5f55\u7684Key\u7531\u5c0f\u5230\u5927\u6392\u5217\u7684\u3002<br \/>\nLevelDB\u5c06SST\u6587\u4ef6\u5b9a\u4e49\u4e3aTable\uff0c\u6bcf\u4e2aTable\u53c8\u5212\u5206\u4e3a\u591a\u4e2a\u8fde\u7eed\u7684Block\uff0c\u6bcf\u4e2aBlock\u4e2d\u53c8\u5b58\u50a8\u591a\u6761\u6570\u636eEntry\uff1a<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/SST%E6%96%87%E4%BB%B6%E7%9A%84%E7%89%A9%E7%90%86%E6%A0%BC%E5%BC%8F.png\" alt=\"SST\u6587\u4ef6\u7684\u7269\u7406\u683c\u5f0f\" \/><br \/>\n\u53ef\u4ee5\u770b\u51fa\uff0c\u5355\u4e2aBlock\u4f5c\u4e3a\u4e00\u4e2a\u72ec\u7acb\u7684\u5199\u5165\u548c\u89e3\u6790\u5355\u4f4d\uff0c\u4f1a\u5728\u5176\u672b\u5c3e\u5b58\u50a8\u4e00\u4e2a\u5b57\u8282\u7684<strong>Type<\/strong>\u548c4\u4e2a\u5b57\u8282\u7684<strong>Crc<\/strong>\uff0c\u5176\u4e2dType\u8bb0\u5f55\u7684\u662f\u5f53\u524dBlock\u7684\u6570\u636e\u538b\u7f29\u7b56\u7565\uff08<a href=\"https:\/\/github.com\/google\/snappy\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">Snappy\u538b\u7f29<\/a>\u6216\u8005\u65e0\u538b\u7f29\u4e24\u79cd\uff09\uff0c\u800cCrc\u5219\u5b58\u50a8Block\u4e2d\u6570\u636e\u7684\u6821\u9a8c\u4fe1\u606f\u3002<br \/>\nBlock\u4e2d\u6bcf\u6761\u6570\u636e<strong>Entry<\/strong>\u662f\u4ee5Key-Value\u65b9\u5f0f\u5b58\u50a8\u7684\uff0c\u5e76\u4e14\u662f\u6309Key\u6709\u5e8f\u5b58\u50a8\uff0cLeveldb\u5f88\u5de7\u5999\u4e86\u5229\u7528\u4e86\u6709\u5e8f\u6570\u7ec4\u76f8\u90bbKey\u53ef\u80fd\u6709\u76f8\u540c\u7684Prefix\u7684\u7279\u70b9\u6765\u51cf\u5c11\u5b58\u50a8\u6570\u636e\u91cf\u3002\u5982\u4e0a\u56fe\u6240\u793a\uff0c\u6bcf\u4e2aEntry\u53ea\u8bb0\u5f55\u81ea\u5df1\u7684Key\u4e0e\u524d\u4e00\u4e2aEntry Key\u7684\u4e0d\u540c\u90e8\u5206\uff0c<br \/>\n\u5728Entry\u5f00\u5934\u8bb0\u5f55\u4e09\u4e2a\u957f\u5ea6\u503c\uff0c\u5206\u522b\u662f\u5f53\u524dEntry\u548c\u5176\u4e4b\u524dEntry\u7684\u516c\u5171Key Prefix\u957f\u5ea6\u3001\u5f53\u524dEntry Key\u81ea\u6709Key\u90e8\u5206\u7684\u957f\u5ea6\u548cValue\u7684\u957f\u5ea6\u3002\u901a\u8fc7\u8fd9\u4e9b\u957f\u5ea6\u4fe1\u606f\u548c\u5176\u540e\u76f8\u90bb\u7684\u7279\u6709Key\u53caValue\u5185\u5bb9\uff0c\u7ed3\u5408\u524d\u4e00\u6761Entry\u7684Key\u5185\u5bb9\uff0c\u6211\u4eec\u53ef\u4ee5\u65b9\u4fbf\u7684\u83b7\u5f97\u5f53\u524dEntry\u7684\u5b8c\u6574Key\u548cValue\u4fe1\u606f\u3002<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb%E8%AE%B0%E5%BD%95%E6%A0%BC%E5%BC%8F2.png\" alt=\"leveldb\u8bb0\u5f55\u683c\u5f0f2\" \/><\/p>\n<p>\u4f8b\u5982\u8981\u987a\u5e8f\u5b58\u50a8Key\u503c<code>\u201capple\u201d = value1<\/code>\u548c<code>\u201capplepen\u201d = value2<\/code>\u7684\u4e24\u6761\u6570\u636e\uff0c\u8fd9\u91cc\u7b2c\u4e8c\u4e2aEntry\u4e2d\uff0ckey\u5171\u4eab\u957f\u5ea6\u4e3a5\uff0ckey\u975e\u5171\u4eab\u957f\u5ea6\u4e3a3\uff0cvalue\u957f\u5ea6\u4e3a6\uff0ckey\u975e\u5171\u4eab\u5185\u5bb9\u4e3a\u201cpen\u201d\uff0cvalue\u5185\u5bb9\u4e3a\u201cvalue2\u201d.<\/p>\n<p>\u8fd9\u79cd\u65b9\u5f0f\u975e\u5e38\u597d\u7684\u51cf\u5c11\u4e86\u6570\u636e\u5b58\u50a8\uff0c\u4f46\u540c\u65f6\u4e5f\u5f15\u5165\u4e00\u4e2a\u98ce\u9669\uff0c\u5982\u679c\u6700\u5f00\u5934\u7684Entry\u6570\u636e\u635f\u574f\uff0c\u5176\u540e\u7684\u6240\u6709Entry\u90fd\u5c06\u65e0\u6cd5\u6062\u590d\u3002\u4e3a\u4e86\u964d\u4f4e\u8fd9\u4e2a\u98ce\u9669\uff0cleveldb\u5f15\u5165\u4e86<strong>\u91cd\u542f\u70b9<\/strong>\uff0c\u6bcf\u9694\u56fa\u5b9a\u6761\u6570Entry\u4f1a\u5f3a\u5236\u52a0\u5165\u4e00\u4e2a\u91cd\u542f\u70b9\uff0c\u8fd9\u4e2a\u4f4d\u7f6e\u7684Entry\u4f1a\u5b8c\u6574\u7684\u8bb0\u5f55\u81ea\u5df1\u7684Key\uff0c\u5e76\u5c06\u5176shared\u503c\u8bbe\u7f6e\u4e3a0\u3002\u540c\u65f6\uff0cBlock\u4f1a\u5c06\u8fd9\u4e9b\u91cd\u542f\u70b9\u7684\u504f\u79fb\u91cf\u53ca\u4e2a\u6570\u8bb0\u5f55\u5728\u6240\u6709Entry\u540e\u8fb9\u7684Tailer\u4e2d\u3002<\/p>\n<h4 id=\"sst\u6587\u4ef6\u7684\u903b\u8f91\u683c\u5f0f\">SST\u6587\u4ef6\u7684\u903b\u8f91\u683c\u5f0f<\/h4>\n<p>Table\u4e2d\u4e0d\u540c\u7684Block\u7269\u7406\u4e0a\u7684\u5b58\u50a8\u65b9\u5f0f\u4e00\u81f4\uff0c\u5982\u4e0a\u6587\u6240\u793a\uff0c\u4f46\u5728\u903b\u8f91\u4e0a\u53ef\u80fd\u5b58\u50a8\u4e0d\u540c\u7684\u5185\u5bb9\uff0c\u5305\u62ec\u5b58\u50a8\u6570\u636e\u7684Block\uff0c\u5b58\u50a8\u7d22\u5f15\u4fe1\u606f\u7684Block\uff0c\u5b58\u50a8Filter\u7684Block\uff1a<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldbssttable%E9%80%BB%E8%BE%91.jpg\" alt=\"leveldbssttable\u903b\u8f91\" \/><\/p>\n<ul>\n<li>Data Block:<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb-datablock.png\" alt=\"leveldb-datablock -w500\" \/><br \/>\n\u4ece\u56fe\u4e2d\u53ef\u4ee5\u770b\u51fa\uff0c\u5176\u5185\u90e8\u4e5f\u5206\u4e3a\u4e24\u4e2a\u90e8\u5206\uff0c\u524d\u9762\u662f\u4e00\u4e2a\u4e2aKV\u8bb0\u5f55\uff0c\u5176\u987a\u5e8f\u662f\u6839\u636eKey\u503c\u7531\u5c0f\u5230\u5927\u6392\u5217\u7684\uff0c\u5728Block\u5c3e\u90e8\u5219\u662f\u4e00\u4e9b\u201c\u91cd\u542f\u70b9\u201d\uff08Restart Point\uff09,\u5176\u5b9e\u662f\u4e00\u4e9b\u6307\u9488\uff0c\u6307\u51faBlock\u5185\u5bb9\u4e2d\u7684\u4e00\u4e9b\u8bb0\u5f55\u4f4d\u7f6e\u3002<\/li>\n<li>Footer\uff1a\u4e3a\u4e8eTable\u5c3e\u90e8\uff0c\u8bb0\u5f55\u6307\u5411Metaindex Block\u7684Handle\u548c\u6307\u5411Index Block\u7684Handle\u3002\u9700\u8981\u8bf4\u660e\u7684\u662fTable\u4e2d\u6240\u6709\u7684Handle\u662f\u901a\u8fc7\u504f\u79fb\u91cfOffset\u4ee5\u53caSize\u4e00\u540c\u6765\u8868\u793a\u7684\uff0c\u7528\u6765\u6307\u660e\u6240\u6307\u5411\u7684Block\u4f4d\u7f6e\u3002Footer\u662fSST\u6587\u4ef6\u89e3\u6790\u5f00\u59cb\u7684\u5730\u65b9\uff0c\u901a\u8fc7Footer\u4e2d\u8bb0\u5f55\u7684\u8fd9\u4e24\u4e2a\u5173\u952e\u5143\u4fe1\u606fBlock\u7684\u4f4d\u7f6e\uff0c\u53ef\u4ee5\u65b9\u4fbf\u7684\u5f00\u542f\u4e4b\u540e\u7684\u89e3\u6790\u5de5\u4f5c\u3002\u53e6\u5916Footer\u4e2d\u8fd8\u8bb0\u5f55\u4e86\u7528\u4e8e\u9a8c\u8bc1\u6587\u4ef6\u662f\u5426\u4e3a\u5408\u6cd5SST\u6587\u4ef6\u7684\u5e38\u6570\u503cMagic num\u3002<\/li>\n<li>Index Block\uff1a\u8bb0\u5f55Data Block\u4f4d\u7f6e\u4fe1\u606f\u7684Block\uff0c\u5176\u4e2d\u7684\u6bcf\u4e00\u6761Entry\u6307\u5411\u4e00\u4e2aData Block\uff0c\u5176Key\u503c\u4e3a\u6240\u6307\u5411\u7684Data Block\u6700\u540e\u4e00\u6761\u6570\u636e\u7684Key\uff0cValue\u4e3a\u6307\u5411\u8be5Data Block\u4f4d\u7f6e\u7684Handle\b\u3002<\/li>\n<li>Metaindex Block\uff1a\u4e0eIndex Block\u7c7b\u4f3c\uff0c\u7531\u4e00\u7ec4Handle\u7ec4\u6210\uff0c\u4e0d\u540c\u7684\u662f\u8fd9\u91cc\u7684Handle\u6307\u5411\u7684Meta Block\u3002<\/li>\n<\/ul>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"null\">Data Block\uff1a\u4ee5Key-Value\u7684\u65b9\u5f0f\u5b58\u50a8\u5b9e\u9645\u6570\u636e\uff0c\u5176\u4e2dKey\u5b9a\u4e49\u4e3a\uff1a\r\nDataBlock Key := UserKey + SequenceNum + Type \r\n\/\/\u5bf9\u6bd4Memtable\u4e2d\u7684Key\uff0c\u53ef\u4ee5\u53d1\u73b0Data Block\u4e2d\u7684Key\u5e76\u6ca1\u6709\u62fc\u63a5UserKey\u7684\u957f\u5ea6\u5728UserKey\u524d\uff0c\r\n\/\/\u8fd9\u662f\u7531\u4e8e\u4e0a\u9762\u8bb2\u5230\u7684\u7269\u7406\u7ed3\u6784\u4e2d\u5df2\u7ecf\u6709\u4e86Key\u7684\u957f\u5ea6\u4fe1\u606f\u3002\r\nType := kDelete or kValue<\/pre>\n<ul>\n<li>Meta Block\uff1a\u6bd4\u8f83\u7279\u6b8a\u7684Block\uff0c\u7528\u6765\u5b58\u50a8\u5143\u4fe1\u606f\uff0c\u76ee\u524dLevelDB\u4f7f\u7528\u7684\u4ec5\u6709\u5bf9\u5e03\u9686\u8fc7\u6ee4\u5668\u7684\u5b58\u50a8\u3002\u5199\u5165Data Block\u7684\u6570\u636e\u4f1a\u540c\u65f6\u66f4\u65b0\u5bf9\u5e94Meta Block\u4e2d\u7684\u8fc7\u6ee4\u5668\u3002\u8bfb\u53d6\u6570\u636e\u65f6\u4e5f\u4f1a\u9996\u5148\u7ecf\u8fc7\u5e03\u9686\u8fc7\u6ee4\u5668\u8fc7\u6ee4\u3002Meta Block\u7684\u7269\u7406\u7ed3\u6784\u4e5f\u4e0e\u5176\u4ed6Block\u6709\u6240\u4e0d\u540c\uff1a<\/li>\n<\/ul>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"null\">[filter 0]\r\n[filter 1]\r\n[filter 2]\r\n... \r\n[filter N-1]\r\n[offset of filter 0] : 4 bytes\r\n[offset of filter 1] : 4 bytes\r\n[offset of filter 2] : 4 bytes\r\n... \r\n[offset of filter N-1] : 4 bytes\r\n[offset of beginning of offset array] : 4 bytes\r\nlg(base) : 1 byte<\/pre>\n<p>\u5176\u4e2d\u6bcf\u4e2afilter\u8282\u5bf9\u5e94\u4e00\u6bb5Key Range\uff0c\u843d\u5728\u67d0\u4e2aKey Range\u7684Key\u9700\u8981\u5230\u5bf9\u5e94\u7684filter\u8282\u4e2d\u67e5\u627e\u81ea\u5df1\u7684\u8fc7\u6ee4\u4fe1\u606f\uff0cbase\u6307\u5b9a\u8fd9\u4e2aRange\u7684\u5927\u5c0f\u3002<\/p>\n<h3 id=\"manifest\u6587\u4ef6\">Manifest\u6587\u4ef6<\/h3>\n<p>Manifest\u6587\u4ef6\u4e2d\u8bb0\u5f55SST\u6587\u4ef6\u5728\u4e0d\u540cLevel\u7684\u5206\u5e03\uff0c\u5355\u4e2aSST\u6587\u4ef6\u7684\u6700\u5927\u6700\u5c0fkey\uff0c\u4ee5\u53ca\u5176\u4ed6\u4e00\u4e9bLevelDB\u9700\u8981\u7684\u5143\u4fe1\u606f\u3002<br \/>\nSSTable\u4e2d\u7684\u67d0\u4e2a\u6587\u4ef6\u5c5e\u4e8e\u7279\u5b9a\u5c42\u7ea7\uff0c\u800c\u4e14\u5176\u5b58\u50a8\u7684\u8bb0\u5f55\u662fkey\u6709\u5e8f\u7684\uff0c\u90a3\u4e48\u5fc5\u7136\u6709\u6587\u4ef6\u4e2d\u7684\u6700\u5c0fkey\u548c\u6700\u5927key\uff0c\u8fd9\u662f\u975e\u5e38\u91cd\u8981\u7684\u4fe1\u606f\uff0cLevelDb\u5e94\u8be5\u8bb0\u4e0b\u8fd9\u4e9b\u4fe1\u606f\u3002Manifest\u5c31\u662f\u5e72\u8fd9\u4e2a\u7684<\/p>\n<h3 id=\"current\u6587\u4ef6\">Current\u6587\u4ef6<\/h3>\n<p>\u4ece\u4e0a\u9762\u7684\u4ecb\u7ecd\u53ef\u4ee5\u770b\u51fa\uff0cLevelDB\u542f\u52a8\u65f6\u7684\u9996\u8981\u4efb\u52a1\u5c31\u662f\u627e\u5230\u5f53\u524d\u7684Manifest\uff0c\u800cManifest\u53ef\u80fd\u6709\u591a\u4e2a\u3002Current\u6587\u4ef6\u7b80\u5355\u7684\u8bb0\u5f55\u4e86\u5f53\u524dManifest\u7684\u6587\u4ef6\u540d\uff0c\u4ece\u800c\u8ba9\u8fd9\u4e2a\u8fc7\u7a0b\u53d8\u5f97\u975e\u5e38\u7b80\u5355\u3002<br \/>\nCurrent\u6587\u4ef6\u7684\u5185\u5bb9\u53ea\u6709\u4e00\u4e2a\u4fe1\u606f\uff0c\u5c31\u662f\u8bb0\u8f7d\u5f53\u524d\u7684manifest\u6587\u4ef6\u540d\u3002\u56e0\u4e3a\u5728LevleDb\u7684\u8fd0\u884c\u8fc7\u7a0b\u4e2d\uff0c\u968f\u7740Compaction\u7684\u8fdb\u884c\uff0cSSTable\u6587\u4ef6\u4f1a\u53d1\u751f\u53d8\u5316\uff0c\u4f1a\u6709\u65b0\u7684\u6587\u4ef6\u4ea7\u751f\uff0c\u8001\u7684\u6587\u4ef6\u88ab\u5e9f\u5f03\uff0cManifest\u4e5f\u4f1a\u8ddf\u7740\u53cd\u6620\u8fd9\u79cd\u53d8\u5316\uff0c\u6b64\u65f6\u5f80\u5f80\u4f1a\u65b0\u751f\u6210Manifest\u6587\u4ef6\u6765\u8bb0\u8f7d\u8fd9\u79cd\u53d8\u5316\uff0c\u800cCurrent\u5219\u7528\u6765\u6307\u51fa\u54ea\u4e2aManifest\u6587\u4ef6\u624d\u662f\u6211\u4eec\u5173\u5fc3\u7684\u90a3\u4e2aManifest\u6587\u4ef6\u3002<\/p>\n<h2 id=\"\u4e3b\u8981\u64cd\u4f5c\">\u4e3b\u8981\u64cd\u4f5c<\/h2>\n<h3 id=\"\u8bfb\u5199\u64cd\u4f5c\">\u8bfb\u5199\u64cd\u4f5c<\/h3>\n<h4 id=\"\u5199\u6d41\u7a0b\">\u5199\u6d41\u7a0b<\/h4>\n<p>LevelDB\u7684\u5199\u64cd\u4f5c\u5305\u62ec\u8bbe\u7f6ekey-value\u548c\u5220\u9664key\u4e24\u79cd\u3002\u9700\u8981\u6307\u51fa\u7684\u662f\u8fd9\u4e24\u79cd\u60c5\u51b5\u5728LevelDB\u7684\u5904\u7406\u4e0a\u662f\u4e00\u81f4\u7684\uff0c\u5220\u9664\u64cd\u4f5c\u5176\u5b9e\u662f\u5411LevelDB\u63d2\u5165\u4e00\u6761\u6807\u8bc6\u4e3a\u5220\u9664\u7684\u6570\u636e\u3002<br \/>\nMemtable\u5e76\u4e0d\u5b58\u5728\u771f\u6b63\u7684\u5220\u9664\u64cd\u4f5c\uff0c\u5220\u9664\u67d0\u4e2aKey\u7684Value\u5728Memtable\u5185\u662f\u4f5c\u4e3a\u63d2\u5165\u4e00\u6761\u8bb0\u5f55\u5b9e\u65bd\u7684\uff0c\u4f46\u662f\u4f1a\u6253\u4e0a\u4e00\u4e2aKey\u7684\u5220\u9664\u6807\u8bb0\uff0c\u771f\u6b63\u7684\u5220\u9664\u64cd\u4f5c\u662fLazy\u7684\uff0c\u4f1a\u5728\u4ee5\u540e\u7684Compaction\u8fc7\u7a0b\u4e2d\u53bb\u6389\u8fd9\u4e2aKV\u3002<br \/>\n<img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb%E5%86%99%E5%85%A5.png\" alt=\"leveldb\u5199\u5165\" \/><br \/>\n\u4ece\u56fe\u4e2d\u53ef\u4ee5\u770b\u51fa\uff0c\u5bf9\u4e8e\u4e00\u4e2a\u63d2\u5165\u64cd\u4f5cPut(Key,Value)\u6765\u8bf4\uff0c\u5b8c\u6210\u63d2\u5165\u64cd\u4f5c\u5305\u542b\u4e24\u4e2a\u5177\u4f53\u6b65\u9aa4\uff1a<br \/>\n\u9996\u5148\u662f\u5c06\u8fd9\u6761KV\u8bb0\u5f55\u4ee5\u987a\u5e8f\u5199\u7684\u65b9\u5f0f\u8ffd\u52a0\u5230\u4e4b\u524d\u4ecb\u7ecd\u8fc7\u7684log\u6587\u4ef6\u672b\u5c3e\uff0c\u56e0\u4e3a\u5c3d\u7ba1\u8fd9\u662f\u4e00\u4e2a\u78c1\u76d8\u8bfb\u5199\u64cd\u4f5c\uff0c\u4f46\u662f\u6587\u4ef6\u7684\u987a\u5e8f\u8ffd\u52a0\u5199\u5165\u6548\u7387\u662f\u5f88\u9ad8\u7684\uff0c\u6240\u4ee5\u5e76\u4e0d\u4f1a\u5bfc\u81f4\u5199\u5165\u901f\u5ea6\u7684\u964d\u4f4e\uff1b<br \/>\n\u7b2c\u4e8c\u4e2a\u6b65\u9aa4\u662f:\u5982\u679c\u5199\u5165log\u6587\u4ef6\u6210\u529f\uff0c\u90a3\u4e48\u5c06\u8fd9\u6761KV\u8bb0\u5f55\u63d2\u5165\u5185\u5b58\u4e2d\u7684Memtable\u4e2d\uff0c\u524d\u9762\u4ecb\u7ecd\u8fc7\uff0cMemtable\u53ea\u662f\u4e00\u5c42\u5c01\u88c5\uff0c\u5176\u5185\u90e8\u5176\u5b9e\u662f\u4e00\u4e2aKey\u6709\u5e8f\u7684SkipList\u5217\u8868\uff0c\u63d2\u5165\u4e00\u6761\u65b0\u8bb0\u5f55\u7684\u8fc7\u7a0b\u4e5f\u5f88\u7b80\u5355\uff0c\u5373\u5148\u67e5\u627e\u5408\u9002\u7684\u63d2\u5165\u4f4d\u7f6e\uff0c\u7136\u540e\u4fee\u6539\u76f8\u5e94\u7684\u94fe\u63a5\u6307\u9488\u5c06\u65b0\u8bb0\u5f55\u63d2\u5165\u5373\u53ef\u3002\u5b8c\u6210\u8fd9\u4e00\u6b65\uff0c\u5199\u5165\u8bb0\u5f55\u5c31\u7b97\u5b8c\u6210\u4e86\u3002<br \/>\n\u6240\u4ee5\u4e00\u4e2a\u63d2\u5165\u8bb0\u5f55\u64cd\u4f5c\u6d89\u53ca\u4e00\u6b21\u78c1\u76d8\u6587\u4ef6\u8ffd\u52a0\u5199\u548c\u5185\u5b58SkipList\u63d2\u5165\u64cd\u4f5c\uff0c\u8fd9\u662f\u4e3a\u4f55levelDb\u5199\u5165\u901f\u5ea6\u5982\u6b64\u9ad8\u6548\u7684\u6839\u672c\u539f\u56e0\u3002<br \/>\nLevelDb\u7684\u63a5\u53e3\u6ca1\u6709\u76f4\u63a5\u652f\u6301\u66f4\u65b0\u64cd\u4f5c\u7684\u63a5\u53e3\uff0c\u5982\u679c\u9700\u8981\u66f4\u65b0\u67d0\u4e2aKey\u7684Value,\u4f60\u53ef\u4ee5\u9009\u62e9\u76f4\u63a5\u751f\u731b\u5730\u63d2\u5165\u65b0\u7684KV\uff0c\u4fdd\u6301Key\u76f8\u540c\uff0c\u8fd9\u6837\u7cfb\u7edf\u5185\u7684key\u5bf9\u5e94\u7684value\u5c31\u4f1a\u88ab\u66f4\u65b0\uff1b\u6216\u8005\u4f60\u53ef\u4ee5\u5148\u5220\u9664\u65e7\u7684KV\uff0c \u4e4b\u540e\u518d\u63d2\u5165\u65b0\u7684KV\uff0c\u8fd9\u6837\u6bd4\u8f83\u59d4\u5a49\u5730\u5b8c\u6210KV\u7684\u66f4\u65b0\u64cd\u4f5c\u3002<\/p>\n<h4 id=\"\u8bfb\u6d41\u7a0b\">\u8bfb\u6d41\u7a0b<\/h4>\n<p><img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb%E8%AF%BB%E5%8F%96.png\" alt=\"leveldb\u8bfb\u53d6\" \/><\/p>\n<p>\u9996\u5148\uff0c\u751f\u6210\u5185\u90e8\u67e5\u8be2\u6240\u7528\u7684Key\uff0c\u7528\u751f\u6210\u7684Key\uff0c\u4f9d\u6b21\u5c1d\u8bd5\u4ece Memtable\uff0cImmtable\u4ee5\u53caSST\u6587\u4ef6\u4e2d\u8bfb\u53d6\uff0c\u76f4\u5230\u627e\u5230\uff08\u6216\u8005\u67e5\u5230\u6700\u9ad8level\uff0c\u67e5\u627e\u5931\u8d25\uff0c\u8bf4\u660e\u6574\u4e2a\u7cfb\u7edf\u4e2d\u4e0d\u5b58\u5728\u8fd9\u4e2aKey)\u3002<br \/>\n\u4ece\u4fe1\u606f\u7684\u66f4\u65b0\u65f6\u95f4\u6765\u8bf4\uff0c\u5f88\u660e\u663eMemtable\u5b58\u50a8\u7684\u662f\u6700\u65b0\u9c9c\u7684KV\u5bf9\uff1bImmutable Memtable\u4e2d\u5b58\u50a8\u7684KV\u6570\u636e\u5bf9\u7684\u65b0\u9c9c\u7a0b\u5ea6\u6b21\u4e4b\uff1b\u800c\u6240\u6709SSTable\u6587\u4ef6\u4e2d\u7684KV\u6570\u636e\u65b0\u9c9c\u7a0b\u5ea6\u4e00\u5b9a\u4e0d\u5982\u5185\u5b58\u4e2d\u7684Memtable\u548cImmutable Memtable\u7684\u3002\u5bf9\u4e8eSSTable\u6587\u4ef6\u6765\u8bf4\uff0c\u5982\u679c\u540c\u65f6\u5728level L\u548cLevel L+1\u627e\u5230\u540c\u4e00\u4e2akey\uff0clevel L\u7684\u4fe1\u606f\u4e00\u5b9a\u6bd4level L+1\u7684\u8981\u65b0\u3002\u4e5f\u5c31\u662f\u8bf4\uff0c\u4e0a\u9762\u5217\u51fa\u7684\u67e5\u627e\u8def\u5f84\u5c31\u662f\u6309\u7167\u6570\u636e\u65b0\u9c9c\u7a0b\u5ea6\u6392\u5217\u51fa\u6765\u7684\uff0c\u8d8a\u65b0\u9c9c\u7684\u8d8a\u5148\u67e5\u627e\u3002<\/p>\n<p>\u4e3e\u4e2a\u4f8b\u5b50\u3002\u6bd4\u5982\u6211\u4eec\u5148\u5f80levelDb\u91cc\u9762\u63d2\u5165\u4e00\u6761\u6570\u636e\u00a0<code>{key=\"www.samecity.com\" value=\"\u6211\u4eec\"}<\/code>,\u8fc7\u4e86\u51e0\u5929\uff0csamecity\u7f51\u7ad9\u6539\u540d\u4e3a\uff1a69\u540c\u57ce\uff0c\u6b64\u65f6\u6211\u4eec\u63d2\u5165\u6570\u636e<code>{key=\"www.samecity.com\" value=\"69\u540c\u57ce\"}<\/code>\uff0c\u540c\u6837\u7684key,\u4e0d\u540c\u7684value\uff1b\u903b\u8f91\u4e0a\u7406\u89e3\u597d\u50cflevelDb\u4e2d\u53ea\u6709\u4e00\u4e2a\u5b58\u50a8\u8bb0\u5f55\uff0c\u5373\u7b2c\u4e8c\u4e2a\u8bb0\u5f55\uff0c\u4f46\u662f\u5728levelDb\u4e2d\u5f88\u53ef\u80fd\u5b58\u5728\u4e24\u6761\u8bb0\u5f55\uff0c\u5373\u4e0a\u9762\u7684\u4e24\u4e2a\u8bb0\u5f55\u90fd\u5728levelDb\u4e2d\u5b58\u50a8\u4e86\uff0c\u6b64\u65f6\u5982\u679c\u7528\u6237\u67e5\u8be2<code>key=\"www.samecity.com\"<\/code>,\u6211\u4eec\u5f53\u7136\u5e0c\u671b\u627e\u5230\u6700\u65b0\u7684\u66f4\u65b0\u8bb0\u5f55\uff0c\u4e5f\u5c31\u662f\u7b2c\u4e8c\u4e2a\u8bb0\u5f55\u8fd4\u56de\uff0c\u8fd9\u5c31\u662f\u4e3a\u4f55\u8981\u4f18\u5148\u67e5\u627e\u65b0\u9c9c\u6570\u636e\u7684\u539f\u56e0\u3002<\/p>\n<p>\u4eceSST\u6587\u4ef6\u4e2d\u67e5\u627e\u9700\u8981\u4f9d\u6b21\u5c1d\u8bd5\u5728\u6bcf\u4e00\u5c42\u4e2d\u8bfb\u53d6\uff0c\u5f97\u76ca\u4e8eManifest\u4e2d\u8bb0\u5f55\u7684\u6bcf\u4e2a\u6587\u4ef6\u7684key\u533a\u95f4\uff0c\u6211\u4eec\u53ef\u4ee5\u5f88\u65b9\u4fbf\u7684\u77e5\u9053\u67d0\u4e2akey\u662f\u5426\u5728\u6587\u4ef6\u4e2d\u3002<code>Level 0<\/code>\u7684\u6587\u4ef6\u7531\u4e8e\u76f4\u63a5\u7531Immutable Dump \u4ea7\u751f\uff0c\u4e0d\u53ef\u907f\u514d\u7684\u4f1a\u76f8\u4e92\u91cd\u53e0\uff0c\u6240\u4ee5\u9700\u8981\u5bf9\u6bcf\u4e2a\u6587\u4ef6\u4f9d\u6b21\u67e5\u627e\u3002\u5bf9\u4e8e\u5176\u4ed6\u5c42\u6b21\uff0c\u7531\u4e8e\u5f52\u5e76\u8fc7\u7a0b\u4fdd\u8bc1\u4e86\u5176\u4e92\u76f8\u4e0d\u91cd\u53e0\u4e14\u6709\u5e8f\uff0c\u4e8c\u5206\u67e5\u627e\u7684\u65b9\u5f0f\u63d0\u4f9b\u4e86\u66f4\u597d\u7684\u67e5\u8be2\u6548\u7387\u3002<br \/>\n\u53ef\u4ee5\u770b\u51fa\u540c\u4e00\u4e2aKey\u51fa\u73b0\u5728\u4e0a\u5c42\u7684\u64cd\u4f5c\u4f1a\u5c4f\u853d\u4e0b\u5c42\u7684\u3002\u4e5f\u56e0\u6b64\u5220\u9664Key\u65f6\u53ea\u9700\u8981\u5728Memtable\u538b\u5165\u4e00\u6761\u6807\u8bb0\u4e3a\u5220\u9664\u7684\u6761\u76ee\u5373\u53ef\u3002\u88ab\u5176\u5c4f\u853d\u7684\u6240\u6709\u6761\u76ee\u4f1a\u5728\u4e4b\u540e\u7684\u5f52\u5e76\u8fc7\u7a0b\u4e2d\u6e05\u9664\u3002<br \/>\n\u76f8\u5bf9\u5199\u64cd\u4f5c\uff0c\u8bfb\u64cd\u4f5c\u5904\u7406\u8d77\u6765\u8981\u590d\u6742\u5f88\u591a\uff0c\u6240\u4ee5\u5199\u7684\u901f\u5ea6\u5fc5\u7136\u8981\u8fdc\u8fdc\u9ad8\u4e8e\u8bfb\u6570\u636e\u7684\u901f\u5ea6\uff0c\u4e5f\u5c31\u662f\u8bf4\uff0cLevelDb\u6bd4\u8f83\u9002\u5408\u5199\u64cd\u4f5c\u591a\u4e8e\u8bfb\u64cd\u4f5c\u7684\u5e94\u7528\u573a\u5408\u3002\u800c\u5982\u679c\u5e94\u7528\u662f\u5f88\u591a\u8bfb\u64cd\u4f5c\u7c7b\u578b\u7684\uff0c\u90a3\u4e48\u987a\u5e8f\u8bfb\u53d6\u6548\u7387\u4f1a\u6bd4\u8f83\u9ad8\uff0c\u56e0\u4e3a\u8fd9\u6837\u5927\u90e8\u5206\u5185\u5bb9\u90fd\u4f1a\u5728\u7f13\u5b58\u4e2d\u627e\u5230\uff0c\u5c3d\u53ef\u80fd\u907f\u514d\u5927\u91cf\u7684\u968f\u673a\u8bfb\u53d6\u64cd\u4f5c\u3002<\/p>\n<h5 id=\"leveldb\u4e2d\u7684cache\">levelDb\u4e2d\u7684Cache<\/h5>\n<p>\u8bfb\u53d6\u64cd\u4f5c\u5982\u679c\u6ca1\u6709\u5728\u5185\u5b58\u7684memtable\u4e2d\u627e\u5230\u8bb0\u5f55\uff0c\u8981\u591a\u6b21\u8fdb\u884c\u78c1\u76d8\u8bbf\u95ee\u64cd\u4f5c\u3002\u5047\u8bbe\u6700\u4f18\u60c5\u51b5\uff0c\u5373\u7b2c\u4e00\u6b21\u5c31\u5728level 0\u4e2d\u6700\u65b0\u7684\u6587\u4ef6\u4e2d\u627e\u5230\u4e86\u8fd9\u4e2akey\uff0c\u90a3\u4e48\u4e5f\u9700\u8981\u8bfb\u53d62\u6b21\u78c1\u76d8\uff0c\u4e00\u6b21\u662f\u5c06SSTable\u7684\u6587\u4ef6\u4e2d\u7684index\u90e8\u5206\u8bfb\u5165\u5185\u5b58\uff0c\u8fd9\u6837\u6839\u636e\u8fd9\u4e2aindex\u53ef\u4ee5\u786e\u5b9akey\u662f\u5728\u54ea\u4e2ablock\u4e2d\u5b58\u50a8\uff1b\u7b2c\u4e8c\u6b21\u662f\u8bfb\u5165\u8fd9\u4e2ablock\u7684\u5185\u5bb9\uff0c\u7136\u540e\u5728\u5185\u5b58\u4e2d\u67e5\u627ekey\u5bf9\u5e94\u7684value\u3002<br \/>\nlevelDb\u4e2d\u5f15\u5165\u4e86\u4e24\u4e2a\u4e0d\u540c\u7684Cache\uff1a Table Cache \u548c Block Cache\u3002\u5176\u4e2dBlock Cache\u662f\u914d\u7f6e\u53ef\u9009\u7684\uff0c\u5373\u5728\u914d\u7f6e\u6587\u4ef6\u4e2d\u6307\u5b9a\u662f\u5426\u6253\u5f00\u8fd9\u4e2a\u529f\u80fd\u3002<\/p>\n<p><img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb%20table%20cache.png\" alt=\"leveldb table cache\" \/><\/p>\n<p>\u5728Cache\u4e2d\uff0ckey\u503c\u662fSSTable\u7684\u6587\u4ef6\u540d\u79f0\uff0cValue\u90e8\u5206\u5305\u542b\u4e24\u90e8\u5206\uff0c\u4e00\u4e2a\u662f\u6307\u5411\u78c1\u76d8\u6253\u5f00\u7684SSTable\u6587\u4ef6\u7684\u6587\u4ef6\u6307\u9488\uff0c\u8fd9\u662f\u4e3a\u4e86\u65b9\u4fbf\u8bfb\u53d6\u5185\u5bb9\uff1b\u53e6\u5916\u4e00\u4e2a\u662f\u6307\u5411\u5185\u5b58\u4e2d\u8fd9\u4e2aSSTable\u6587\u4ef6\u5bf9\u5e94\u7684Table\u7ed3\u6784\u6307\u9488\uff0ctable\u7ed3\u6784\u5728\u5185\u5b58\u4e2d\uff0c\u4fdd\u5b58\u4e86SSTable\u7684index\u5185\u5bb9\u4ee5\u53ca\u7528\u6765\u6307\u793ablock cache\u7528\u7684cache_id ,\u5f53\u7136\u9664\u6b64\u5916\u8fd8\u6709\u5176\u5b83\u4e00\u4e9b\u5185\u5bb9\u3002<br \/>\n\u6bd4\u5982\u5728get(key)\u8bfb\u53d6\u64cd\u4f5c\u4e2d\uff0c\u5982\u679clevelDb\u786e\u5b9a\u4e86key\u5728\u67d0\u4e2alevel\u4e0b\u67d0\u4e2a\u6587\u4ef6A\u7684key range\u8303\u56f4\u5185\uff0c\u90a3\u4e48\u9700\u8981\u5224\u65ad\u662f\u4e0d\u662f\u6587\u4ef6A\u771f\u7684\u5305\u542b\u8fd9\u4e2aKV\u3002\u6b64\u65f6\uff0clevelDb\u4f1a\u9996\u5148\u67e5\u627eTable Cache\uff0c\u770b\u8fd9\u4e2a\u6587\u4ef6\u662f\u5426\u5728\u7f13\u5b58\u91cc\uff0c\u5982\u679c\u627e\u5230\u4e86\uff0c\u90a3\u4e48\u6839\u636eindex\u90e8\u5206\u5c31\u53ef\u4ee5\u67e5\u627e\u662f\u54ea\u4e2ablock\u5305\u542b\u8fd9\u4e2akey\u3002\u5982\u679c\u6ca1\u6709\u5728\u7f13\u5b58\u4e2d\u627e\u5230\u6587\u4ef6\uff0c\u90a3\u4e48\u6253\u5f00SSTable\u6587\u4ef6\uff0c\u5c06\u5176index\u90e8\u5206\u8bfb\u5165\u5185\u5b58\uff0c\u7136\u540e\u63d2\u5165Cache\u91cc\u9762\uff0c\u53bbindex\u91cc\u9762\u5b9a\u4f4d\u54ea\u4e2ablock\u5305\u542b\u8fd9\u4e2aKey \u3002\u5982\u679c\u786e\u5b9a\u4e86\u6587\u4ef6\u54ea\u4e2ablock\u5305\u542b\u8fd9\u4e2akey\uff0c\u90a3\u4e48\u9700\u8981\u8bfb\u5165block\u5185\u5bb9\uff0c\u8fd9\u662f\u7b2c\u4e8c\u6b21\u8bfb\u53d6\u3002<\/p>\n<div class=\"table-box\">\n<table>\n<thead>\n<tr>\n<th align=\"center\">File<br \/>\ncache_id + block_offset<\/th>\n<th align=\"center\">block\u5185\u5bb9<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td align=\"center\">File<br \/>\ncache_id + block_offset<\/td>\n<td align=\"center\">block\u5185\u5bb9<\/td>\n<\/tr>\n<tr>\n<td align=\"center\">File<br \/>\ncache_id + block_offset<\/td>\n<td align=\"center\">block\u5185\u5bb9<\/td>\n<\/tr>\n<tr>\n<td align=\"center\">File<br \/>\ncache_id + block_offset<\/td>\n<td align=\"center\">block\u5185\u5bb9<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Block Cache\u662f\u4e3a\u4e86\u52a0\u5feb\u8fd9\u4e2a\u8fc7\u7a0b\u7684\uff0c\u5982\u4e0a\u56fe\u3002\u5176\u4e2d\u7684key\u662f\u6587\u4ef6\u7684cache_id\u52a0\u4e0a\u8fd9\u4e2ablock\u5728\u6587\u4ef6\u4e2d\u7684\u8d77\u59cb\u4f4d\u7f6eblock_offset\u3002\u800cvalue\u5219\u662f\u8fd9\u4e2aBlock\u7684\u5185\u5bb9\u3002<br \/>\n\u5982\u679clevelDb\u53d1\u73b0\u8fd9\u4e2ablock\u5728block cache\u4e2d\uff0c\u90a3\u4e48\u53ef\u4ee5\u907f\u514d\u8bfb\u53d6\u6570\u636e\uff0c\u76f4\u63a5\u5728cache\u91cc\u7684block\u5185\u5bb9\u91cc\u9762\u67e5\u627ekey\u7684value\u5c31\u884c\uff0c\u5982\u679c\u6ca1\u627e\u5230\u5462\uff1f\u90a3\u4e48\u8bfb\u5165block\u5185\u5bb9\u5e76\u628a\u5b83\u63d2\u5165block cache\u4e2d\u3002levelDb\u5c31\u662f\u8fd9\u6837\u901a\u8fc7\u4e24\u4e2acache\u6765\u52a0\u5feb\u8bfb\u53d6\u901f\u5ea6\u7684\u3002<br \/>\n\u4ece\u8fd9\u91cc\u53ef\u4ee5\u770b\u51fa\uff0c\u5982\u679c\u8bfb\u53d6\u7684\u6570\u636e\u5c40\u90e8\u6027\u6bd4\u8f83\u597d\uff0c\u4e5f\u5c31\u662f\u8bf4\u8981\u8bfb\u7684\u6570\u636e\u5927\u90e8\u5206\u5728cache\u91cc\u9762\u90fd\u80fd\u8bfb\u5230\uff0c\u90a3\u4e48\u8bfb\u53d6\u6548\u7387\u5e94\u8be5\u8fd8\u662f\u5f88\u9ad8\u7684\uff0c\u800c\u5982\u679c\u662f\u5bf9key\u8fdb\u884c\u987a\u5e8f\u8bfb\u53d6\u6548\u7387\u4e5f\u5e94\u8be5\u4e0d\u9519\uff0c\u56e0\u4e3a\u4e00\u6b21\u8bfb\u5165\u540e\u53ef\u4ee5\u591a\u6b21\u88ab\u590d\u7528\u3002\u4f46\u662f\u5982\u679c\u662f\u968f\u673a\u8bfb\u53d6\uff0c\u60a8\u53ef\u4ee5\u63a8\u65ad\u4e0b\u5176\u6548\u7387\u5982\u4f55\u3002<\/p>\n<h3 id=\"\u538b\u7f29\u64cd\u4f5c\">\u538b\u7f29\u64cd\u4f5c<\/h3>\n<p>\u4e3a\u4e86\u52a0\u5feb\u8bfb\u53d6\u901f\u5ea6\uff0clevelDb\u91c7\u53d6\u4e86compaction\u7684\u65b9\u5f0f\u6765\u5bf9\u5df2\u6709\u7684\u8bb0\u5f55\u8fdb\u884c\u6574\u7406\u538b\u7f29\uff0c\u901a\u8fc7\u8fd9\u79cd\u65b9\u5f0f\uff0c\u6765\u5220\u9664\u6389\u4e00\u4e9b\u4e0d\u518d\u6709\u6548\u7684KV\u6570\u636e\uff0c\u51cf\u5c0f\u6570\u636e\u89c4\u6a21\uff0c\u51cf\u5c11\u6587\u4ef6\u6570\u91cf\u7b49\u3002<br \/>\n\u6570\u636e\u538b\u7f29\u662fLevelDB\u4e2d\u91cd\u8981\u7684\u90e8\u5206\uff0c\u5373\u4e0a\u6587\u63d0\u5230\u7684\u5f52\u5e76\u3002\u51b7\u6570\u636e\u4f1a\u968f\u7740Compaction\u4e0d\u65ad\u7684\u4e0b\u79fb\uff0c\u540c\u65f6\u8fc7\u671f\u7684\u6570\u636e\u4e5f\u4f1a\u5728\u5408\u5e76\u8fc7\u7a0b\u4e2d\u88ab\u5220\u9664\u3002<br \/>\nLevelDB\u7684\u538b\u7f29\u64cd\u4f5c\u7531\u5355\u72ec\u7684\u540e\u53f0\u7ebf\u7a0b\u8d1f\u8d23\u3002\u8fd9\u91cc\u7684Compaction\u5305\u62ec\u4e24\u4e2a\u90e8\u5206\uff0cMemtable\u5411Level 0 SST\u6587\u4ef6\u7684Compaction\uff0c\u4ee5\u53caSST\u6587\u4ef6\u5411\u4e0b\u5c42\u7684Compaction\u3002<br \/>\nlevelDb\u7684compaction\u673a\u5236\u548c\u8fc7\u7a0b\u4e0eBigtable\u6240\u8bb2\u8ff0\u7684\u662f\u57fa\u672c\u4e00\u81f4\u7684\uff0cBigtable\u4e2d\u8bb2\u5230\u4e09\u79cd\u7c7b\u578b\u7684compaction: minor \uff0cmajor\u548cfull\u3002\u6240\u8c13minor Compaction\uff0c\u5c31\u662f\u628amemtable\u4e2d\u7684\u6570\u636e\u5bfc\u51fa\u5230SSTable\u6587\u4ef6\u4e2d\uff1bmajor compaction\u5c31\u662f\u5408\u5e76\u4e0d\u540c\u5c42\u7ea7\u7684SSTable\u6587\u4ef6\uff0c\u800cfull compaction\u5c31\u662f\u5c06\u6240\u6709SSTable\u8fdb\u884c\u5408\u5e76\u3002<br \/>\nLevelDb\u5305\u542b\u5176\u4e2d\u4e24\u79cd\uff0cminor\u548cmajor\u3002<\/p>\n<h4 id=\"minor-compaction\">minor compaction<\/h4>\n<p>Minor compaction \u7684\u76ee\u7684\u662f\u5f53\u5185\u5b58\u4e2d\u7684memtable\u5927\u5c0f\u5230\u4e86\u4e00\u5b9a\u503c\u65f6\uff0c\u5c06\u5185\u5bb9\u4fdd\u5b58\u5230\u78c1\u76d8\u6587\u4ef6\u4e2d\uff1a<\/p>\n<p><img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldb-minor%20compaction.png\" alt=\"leveldb-minor compaction\" \/><\/p>\n<p>\u5f53memtable\u6570\u91cf\u5230\u4e86\u4e00\u5b9a\u7a0b\u5ea6\u4f1a\u8f6c\u6362\u4e3aimmutable memtable\uff0c\u6b64\u65f6\u4e0d\u80fd\u5f80\u5176\u4e2d\u5199\u5165\u8bb0\u5f55\uff0c\u53ea\u80fd\u4ece\u4e2d\u8bfb\u53d6KV\u5185\u5bb9\u3002\u4e4b\u524d\u4ecb\u7ecd\u8fc7\uff0cimmutable memtable\u5176\u5b9e\u662f\u4e00\u4e2a\u591a\u5c42\u7ea7\u961f\u5217SkipList\uff0c\u5176\u4e2d\u7684\u8bb0\u5f55\u662f\u6839\u636ekey\u6709\u5e8f\u6392\u5217\u7684\u3002\u6240\u4ee5\u8fd9\u4e2aminor compaction\u5b9e\u73b0\u8d77\u6765\u4e5f\u5f88\u7b80\u5355\uff0c\u5c31\u662f\u6309\u7167immutable memtable\u4e2d\u8bb0\u5f55\u7531\u5c0f\u5230\u5927\u904d\u5386\uff0c\u5e76\u4f9d\u6b21\u5199\u5165\u4e00\u4e2alevel 0\u7684\u65b0\u5efaSSTable\u6587\u4ef6\u4e2d\uff0c\u5199\u5b8c\u540e\u5efa\u7acb\u6587\u4ef6\u7684index\u6570\u636e\uff0c\u8fd9\u6837\u5c31\u5b8c\u6210\u4e86\u4e00\u6b21minor compaction\u3002<br \/>\n<strong>CompactMemTable\u51fd\u6570<\/strong>\u4f1a\u5c06Immutable\u4e2d\u7684\u6570\u636e\u6574\u4f53Dump\u4e3a<code>Level 0<\/code>\u7684\u4e00\u4e2a\u6587\u4ef6\uff0c\u8fd9\u4e2a\u8fc7\u7a0b\u4f1a\u5728Immutable Memtable\u5b58\u5728\u65f6\u88abCompaction\u540e\u53f0\u7ebf\u7a0b\u8c03\u5ea6\u3002<br \/>\n\u8fc7\u7a0b\u6bd4\u8f83\u7b80\u5355\uff0c\u9996\u5148\u4f1a\u83b7\u5f97\u4e00\u4e2aImmutable\u7684Iterator\u7528\u6765\u904d\u5386\u5176\u4e2d\u7684\u6240\u6709\u5185\u5bb9\uff0c\u521b\u5efa\u4e00\u4e2a\u65b0\u7684Level 0 SST\u6587\u4ef6\uff0c\u5e76\u5c06Iterator\u8bfb\u51fa\u7684\u5185\u5bb9\u4f9d\u6b21\u987a\u5e8f\u5199\u5165\u8be5\u6587\u4ef6\u3002\u4e4b\u540e\u66f4\u65b0\u5143\u4fe1\u606f\u5e76\u5220\u9664Immutable Memtable\u3002<\/p>\n<h4 id=\"major-compaction\">major compaction<\/h4>\n<p>\u5f53\u67d0\u4e2alevel\u4e0b\u7684SSTable\u6587\u4ef6\u6570\u76ee\u8d85\u8fc7\u4e00\u5b9a\u8bbe\u7f6e\u503c\u540e\uff0clevelDb\u4f1a\u4ece\u8fd9\u4e2alevel\u7684SSTable\u4e2d\u9009\u62e9\u4e00\u4e2a\u6587\u4ef6\uff08level&gt;0\uff09\uff0c\u5c06\u5176\u548c\u9ad8\u4e00\u5c42\u7ea7\u7684level+1\u7684SSTable\u6587\u4ef6\u5408\u5e76\uff0c\u8fd9\u5c31\u662fmajor compaction\u3002<br \/>\n\u6211\u4eec\u77e5\u9053\u5728\u5927\u4e8e0\u7684\u5c42\u7ea7\u4e2d\uff0c\u6bcf\u4e2aSSTable\u6587\u4ef6\u5185\u7684Key\u90fd\u662f\u7531\u5c0f\u5230\u5927\u6709\u5e8f\u5b58\u50a8\u7684\uff0c\u800c\u4e14\u4e0d\u540c\u6587\u4ef6\u4e4b\u95f4\u7684key\u8303\u56f4\uff08\u6587\u4ef6\u5185\u6700\u5c0fkey\u548c\u6700\u5927key\u4e4b\u95f4\uff09\u4e0d\u4f1a\u6709\u4efb\u4f55\u91cd\u53e0\u3002Level 0\u7684SSTable\u6587\u4ef6\u6709\u4e9b\u7279\u6b8a\uff0c\u5c3d\u7ba1\u6bcf\u4e2a\u6587\u4ef6\u4e5f\u662f\u6839\u636eKey\u7531\u5c0f\u5230\u5927\u6392\u5217\uff0c\u4f46\u662f\u56e0\u4e3alevel 0\u7684\u6587\u4ef6\u662f\u901a\u8fc7minor compaction\u76f4\u63a5\u751f\u6210\u7684\uff0c\u6240\u4ee5\u4efb\u610f\u4e24\u4e2alevel 0\u4e0b\u7684\u4e24\u4e2asstable\u6587\u4ef6\u53ef\u80fd\u518dkey\u8303\u56f4\u4e0a\u6709\u91cd\u53e0\u3002\u6240\u4ee5\u5728\u505amajor compaction\u7684\u65f6\u5019\uff0c\u5bf9\u4e8e\u5927\u4e8elevel 0\u7684\u5c42\u7ea7\uff0c\u9009\u62e9\u5176\u4e2d\u4e00\u4e2a\u6587\u4ef6\u5c31\u884c\uff0c\u4f46\u662f\u5bf9\u4e8elevel 0\u6765\u8bf4\uff0c\u6307\u5b9a\u67d0\u4e2a\u6587\u4ef6\u540e\uff0c\u672clevel\u4e2d\u5f88\u53ef\u80fd\u6709\u5176\u4ed6SSTable\u6587\u4ef6\u7684key\u8303\u56f4\u548c\u8fd9\u4e2a\u6587\u4ef6\u6709\u91cd\u53e0\uff0c\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u8981\u627e\u51fa\u6240\u6709\u6709\u91cd\u53e0\u7684\u6587\u4ef6\u548clevel 1\u7684\u6587\u4ef6\u8fdb\u884c\u5408\u5e76\uff0c\u5373level 0\u5728\u8fdb\u884c\u6587\u4ef6\u9009\u62e9\u7684\u65f6\u5019\uff0c\u53ef\u80fd\u4f1a\u6709\u591a\u4e2a\u6587\u4ef6\u53c2\u4e0emajor compaction\u3002<br \/>\n\u540c\u5c42\u7684\u6587\u4ef6\u8f6e\u6d41\u6765compaction\uff0c\u6bd4\u5982\u8fd9\u6b21\u662f\u6587\u4ef6A\u8fdb\u884ccompaction\uff0c\u90a3\u4e48\u4e0b\u6b21\u5c31\u662f\u5728key range\u4e0a\u7d27\u6328\u7740\u6587\u4ef6A\u7684\u6587\u4ef6B\u8fdb\u884ccompaction\uff0c\u8fd9\u6837\u6bcf\u4e2a\u6587\u4ef6\u90fd\u4f1a\u6709\u673a\u4f1a\u8f6e\u6d41\u548c\u9ad8\u5c42\u7684level \u6587\u4ef6\u8fdb\u884c\u5408\u5e76\u3002\u5982\u679c\u9009\u597d\u4e86level L\u7684\u6587\u4ef6A\u548clevel L+1\u5c42\u7684\u6587\u4ef6\u8fdb\u884c\u5408\u5e76\uff0c\u90a3\u4e48\u95ee\u9898\u53c8\u6765\u4e86\uff0c\u5e94\u8be5\u9009\u62e9level L+1\u54ea\u4e9b\u6587\u4ef6\u8fdb\u884c\u5408\u5e76\uff1flevelDb\u9009\u62e9L+1\u5c42\u4e2d\u548c\u6587\u4ef6A\u5728key range\u4e0a<strong>\u6709\u91cd\u53e0\u7684\u6240\u6709\u6587\u4ef6<\/strong>\u6765\u548c\u6587\u4ef6A\u8fdb\u884c\u5408\u5e76\u3002<\/p>\n<p><img decoding=\"async\" title=\"\" src=\"http:\/\/oc3uwt4a5.bkt.clouddn.com\/leveldbSSTable%20Compaction.png\" alt=\"leveldbSSTable Compaction\" \/><\/p>\n<p>Major compaction\u7684\u8fc7\u7a0b\u5982\u4e0b\uff1a\u5bf9\u591a\u4e2a\u6587\u4ef6\u91c7\u7528<strong>\u591a\u8def\u5f52\u5e76\u6392\u5e8f<\/strong>\u7684\u65b9\u5f0f\uff0c\u4f9d\u6b21\u627e\u51fa\u5176\u4e2d\u6700\u5c0f\u7684Key\u8bb0\u5f55\uff0c\u4e5f\u5c31\u662f\u5bf9\u591a\u4e2a\u6587\u4ef6\u4e2d\u7684\u6240\u6709\u8bb0\u5f55\u91cd\u65b0\u8fdb\u884c\u6392\u5e8f\u3002\u4e4b\u540e\u91c7\u53d6\u4e00\u5b9a\u7684\u6807\u51c6\u5224\u65ad\u8fd9\u4e2aKey\u662f\u5426\u8fd8\u9700\u8981\u4fdd\u5b58\uff0c\u5982\u679c\u5224\u65ad\u6ca1\u6709\u4fdd\u5b58\u4ef7\u503c\uff0c\u90a3\u4e48\u76f4\u63a5\u629b\u6389\uff0c\u5982\u679c\u89c9\u5f97\u8fd8\u9700\u8981\u7ee7\u7eed\u4fdd\u5b58\uff0c\u90a3\u4e48\u5c31\u5c06\u5176\u5199\u5165level L+1\u5c42\u4e2d\u65b0\u751f\u6210\u7684\u4e00\u4e2aSSTable\u6587\u4ef6\u4e2d\u3002\u5c31\u8fd9\u6837\u5bf9KV\u6570\u636e\u4e00\u4e00\u5904\u7406\uff0c\u5f62\u6210\u4e86\u4e00\u7cfb\u5217\u65b0\u7684L+1\u5c42\u6570\u636e\u6587\u4ef6\uff0c\u4e4b\u524d\u7684L\u5c42\u6587\u4ef6\u548cL+1\u5c42\u53c2\u4e0ecompaction \u7684\u6587\u4ef6\u6570\u636e\u6b64\u65f6\u5df2\u7ecf\u6ca1\u6709\u610f\u4e49\u4e86\uff0c\u6240\u4ee5\u5168\u90e8\u5220\u9664\u3002\u8fd9\u6837\u5c31\u5b8c\u6210\u4e86L\u5c42\u548cL+1\u5c42\u6587\u4ef6\u8bb0\u5f55\u7684\u5408\u5e76\u8fc7\u7a0b\u3002<br \/>\n\u90a3\u4e48\u5728major compaction\u8fc7\u7a0b\u4e2d\uff0c\u5224\u65ad\u4e00\u4e2aKV\u8bb0\u5f55\u662f\u5426\u629b\u5f03\u7684\u6807\u51c6\u662f\u4ec0\u4e48\u5462\uff1f\u5176\u4e2d\u4e00\u4e2a\u6807\u51c6\u662f:\u5bf9\u4e8e\u67d0\u4e2akey\u6765\u8bf4\uff0c\u5982\u679c\u5728\u5c0f\u4e8eL\u5c42\u4e2d\u5b58\u5728\u8fd9\u4e2aKey\uff0c\u90a3\u4e48\u8fd9\u4e2aKV\u5728major compaction\u8fc7\u7a0b\u4e2d\u53ef\u4ee5\u629b\u6389\u3002\u56e0\u4e3a\u6211\u4eec\u524d\u9762\u5206\u6790\u8fc7\uff0c\u5bf9\u4e8e\u5c42\u7ea7\u4f4e\u4e8eL\u7684\u6587\u4ef6\u4e2d\u5982\u679c\u5b58\u5728\u540c\u4e00Key\u7684\u8bb0\u5f55\uff0c\u90a3\u4e48\u8bf4\u660e\u5bf9\u4e8eKey\u6765\u8bf4\uff0c\u6709\u66f4\u65b0\u9c9c\u7684Value\u5b58\u5728\uff0c\u90a3\u4e48\u8fc7\u53bb\u7684Value\u5c31\u7b49\u4e8e\u6ca1\u6709\u610f\u4e49\u4e86\uff0c\u6240\u4ee5\u53ef\u4ee5\u5220\u9664\u3002<br \/>\n<strong>BackgroundCompaction\u51fd\u6570<\/strong><br \/>\nSST\u6587\u4ef6\u7684Compaction\u53ef\u4ee5\u7531\u7528\u6237\u901a\u8fc7\u63a5\u53e3\u624b\u52a8\u53d1\u8d77\uff0c\u4e5f\u53ef\u4ee5\u81ea\u52a8\u89e6\u53d1\u3002LevelDB\u4e2d\u89e6\u53d1SST Compaction\u7684\u56e0\u7d20\u5305\u62ecLevel 0 SST\u7684\u4e2a\u6570\uff0c\u5176\u4ed6Level 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1\u5c42\u7684\u4e00\u4e2a\u65b0\u7684SST\u6587\u4ef6\uff0c\u5f52\u5e76\u7684\u8fc7\u7a0b\u4e2d\u5220\u9664\u6240\u6709\u8fc7\u671f\u7684\u6570\u636e\u3002\u5220\u9664\u4e4b\u524d\u7684\u6587\u4ef6\u96c6\u5408\u91cc\u7684\u6240\u6709\u6587\u4ef6\u3002<\/li>\n<\/ul>\n<p>\u901a\u8fc7\u4e0a\u8ff0\u8fc7\u7a0b\u6211\u4eec\u53ef\u4ee5\u770b\u5230\uff0c\u8fd9\u4e2a\u65b0\u751f\u6210\u7684\u6587\u4ef6\u5728\u5176\u6240\u5728Level\u4e0d\u4f1a\u8ddf\u4efb\u4f55\u6587\u4ef6\u6709Key\u7684\u91cd\u53e0\u3002<\/p>\n<h2 id=\"leveldb-\u7684\u7279\u70b9\">LevelDb 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