{"id":4239,"date":"2013-03-08T14:39:34","date_gmt":"2013-03-08T06:39:34","guid":{"rendered":"http:\/\/www.orczhou.com\/?p=4239"},"modified":"2024-07-31T19:00:49","modified_gmt":"2024-07-31T11:00:49","slug":"mysql-source-code-query-optimization-index-merge-structure-cost","status":"publish","type":"post","link":"https:\/\/www.orczhou.com\/index.php\/2013\/03\/mysql-source-code-query-optimization-index-merge-structure-cost\/","title":{"rendered":"index merge\u7684\u6570\u636e\u7ed3\u6784\u548c\u6210\u672c\u8bc4\u4f30"},"content":{"rendered":"<p>\u524d\u9762\u4ee5<a href=\"http:\/\/www.orczhou.com\/index.php\/2013\/01\/mysql-source-code-query-optimization-index-merge\/\" target=\"_blank\" rel=\"noopener\">\u6848\u4f8b\u7684\u5f62\u5f0f<\/a>\u4ecb\u7ecd\u4e86\u4ec0\u4e48\u662findex merge\uff0c\u4ee5\u53ca\u5b83\u7684\u4f7f\u7528\u573a\u666f\u3002\u672c\u6587\u5c06\u4ecb\u7ecdindex merge\u5b9e\u73b0\u7684\u4e3b\u8981\u6570\u636e\u7ed3\u6784\u4ee5\u53caMySQL\u5982\u4f55\u8bc4\u4f30index merge\u7684\u6210\u672c\u3002\u5728\u5f00\u59cb\u672c\u6587\u4e4b\u524d\uff0c\u9700\u8981\u5148\u7406\u89e3Range\u8bbf\u95ee\u76f8\u5173\u7684\u6570\u636e\u7ed3\u6784\u4ecb\u7ecd\uff1a<a href=\"http:\/\/www.orczhou.com\/index.php\/2012\/11\/mysql-source-code-range-optimize-data-structure\/\" target=\"_blank\" rel=\"noopener\">SEL_ARG\u7ed3\u6784<\/a>\uff0c<a href=\"http:\/\/www.orczhou.com\/index.php\/2013\/01\/mysql-source-code-range-optimize-data-structure-again\" target=\"_blank\" rel=\"noopener\">SEL_TREE\u7ed3\u6784<\/a>\u3002<!--more--><\/p>\n\n<h3>1. \u6982\u8ff0:index merge\u7684\u6570\u636e\u7ed3\u6784<\/h3>\n<p>index merge\u7684\u4e3b\u8981\u6570\u636e\u7ed3\u6784\u4ecd\u7136\u662f\u5b58\u653e\u5728SEL_TREE\u4e2d\uff1a<\/p>\n<pre><blockquote>class SEL_TREE :public Sql_alloc\r\n{\r\n...\r\n  List&lt;SEL_IMERGE&gt; merges;\r\n...\r\n};<\/blockquote><\/pre>\n<p>\u5728merges\u8fd9\u4e2alist\u4e2d\u5b58\u653e\u4e86\u6240\u6709\u53ef\u80fd\u7684index merge\u3002\u672c\u6587\u5c06\u4ece\u51e0\u4e2a\u6848\u4f8b\uff0c\u6765\u770b\u770bSEL_TREE\/SEL_IMERGE\u5982\u4f55\u4ee3\u8868\u4e00\u4e2aindex merge\u8bbf\u95ee\u65b9\u5f0f\u3002\u672c\u6587\u5c06\u4e0d\u518d\u91cd\u590d\u4ecb\u7ecdSEL_ARG\/SEL_TREE\u7684Range\u76f8\u5173\u7ed3\u6784\u3002<\/p>\n<p>SEL_IMERGE\u7684\u4e3b\u8981\u6210\u5458\u662f\u4e00\u4e2aSEL_TREE\u7684\u94fe\u8868\uff0c\u6bcf\u4e00\u4e2aSEL_TREE\u4ee3\u8868\u4e86\u4e00\u4e2a\u72ec\u7acb\u7684\u7d22\u5f15\u6761\u4ef6\uff0c\u8fd9\u4e2a\u94fe\u8868\u4e2d\u591a\u4e2a\u6761\u4ef6\u5171\u540c\u6784\u6210\u8fd9\u4e2aindex merge\u3002\u6211\u4eec\u901a\u8fc7\u4e24\u4e2a\u6848\u4f8b\u770b\u770b<strong>\u4e00\u4e2aSEL_TREE\u5982\u4f55\u8868\u793a\u4e00\u4e2aindex merge<\/strong>\u3002(\u8fd9\u91cc\u9700\u8981\u6ce8\u610f\uff0cSEL_TREE\u65e2\u53ef\u4ee5\u4ee3\u8868\u4e00\u4e2aRANGE\u6761\u4ef6\uff0c\u4e5f\u53ef\u4ee5\u4ee3\u8868\u4e00\u4e2aindex merge\uff1b\u4ee3\u8868Range\u65f6\uff0c\u5176merges\u6210\u5458\u4e3a\u7a7a)\u3002<\/p>\n<h3>2. \u6848\u4f8b1:\u7b80\u5355\u7684index merge<\/h3>\n<pre><blockquote>SELECT * FROM tmp_sel_tree where \r\n  ( key1_part1 = 1 or (key1_part2 = 2 and key2_part1 = 3) ) or\r\n  ( key3_part1 = 5 )<\/blockquote><\/pre>\n<p>\u8fd9\u662f\u4e00\u4e2a\u591a\u4e2a\u7d22\u5f15\u7684index merge\uff0c\u4e14\u6ca1\u6709\u4efb\u4f55\u7684range\u53ef\u4ee5\u4f7f\u7528\u3002or\u6761\u4ef6\u7684\u4e09\u4e2a\u5206\u652f\uff0c\u5206\u8868\u53ef\u4ee5\u4f7f\u7528\u4e00\u4e2a\u72ec\u7acb\u7684\u7d22\u5f15\uff0c\u5176\u6784\u6210\u7684SEL_TREE\u7ed3\u6784\u5982\u4e0b\uff1a<\/p>\n<pre><blockquote>SEL_TREE\r\n  |\r\n  |-->List&lt;SEL_IMERGE&gt; merges;\r\n     |\r\n     |              \/ SEL_TREE-> SEL_ARG(key1_part1 = 1)\r\n     \\ SEL_IMERGE1  | SEL_TREE-> SEL_ARG(key2_part1 = 3)\r\n                    \\ SEL_TREE-> SEL_ARG(key3_part1 = 5)<\/blockquote><\/pre>\n<h3>3. \u6848\u4f8b2:\u5355\u4e2a\u67e5\u8be2\u591a\u4e2aindex merge<\/h3>\n<pre><blockquote>SELECT * FROM tmp_sel_tree where \r\n  ( key1_part1 = 1 or (key1_part2 = 2 and key2_part1 = 3) ) and\r\n  ( key3_part1 = 5 or  key2_part1 = 5)<\/blockquote><\/pre>\n<p>\u8fd9\u4e2a\u6848\u4f8b\u4e2d\uff0cAnd\u6761\u4ef6\u4e24\u8fb9\u90fd\u53ef\u4ee5\u5404\u81ea\u4f7f\u7528index merge\uff0cMySQL\u53ef\u4ee5\u9009\u62e9\u5176\u4e2d\u4efb\u4f55\u4e00\u4e2a\u6267\u884c\u3002\u5bf9\u5e94\u7684SEL_TREE\u4e2d\uff0c\u5c06\u4f1a\u6709\u591a\u4e2aSEL_IMERGE\u5bf9\u8c61\uff0c\u6bcf\u4e2aSEL_IMERGE\u5bf9\u8c61\u91cc\u9762\u5b58\u50a8\u4e86\u591a\u4e2a\u72ec\u7acb\u7684\u53ef\u4ee5\u4f7f\u7528\u7d22\u5f15\u7684\u6761\u4ef6(\u6709\u72ec\u7acb\u7684SEL_TREE\u8868\u793a)\uff1a<\/p>\n<pre><blockquote>SEL_TREE\r\n  |\r\n  \\-->List&lt;SEL_IMERGE&gt; merges;\r\n     |\r\n     |              \/ SEL_TREE-> SEL_ARG(key1_part1 = 1)\r\n     | SEL_IMERGE1  | SEL_TREE-> SEL_ARG(key2_part1 = 3)\r\n     |              \\ SEL_TREE-> SEL_ARG(key3_part1 = 5)\r\n     |\r\n     |              \/ SEL_TREE-> SEL_ARG(key2_part1 = 5)\r\n     \\ SEL_IMERGE2  | \r\n                    \\ SEL_TREE-> SEL_ARG(key3_part1 = 5)<\/blockquote><\/pre>\n<p>MySQL\u4f1a\u5728\u9009\u62e9\u6267\u884c\u8ba1\u5212\u65f6\uff0c\u9010\u4e00\u8bc4\u4f30\u6bcf\u4e2aSEL_IMERGE\u7684\u6210\u672c\uff0c\u7136\u540e\u9009\u62e9\u6700\u4f18\u7684\u6267\u884c\u8ba1\u5212\u3002<\/p>\n<h3>4. \u6210\u672c\u8ba1\u7b97<\/h3>\n<p>MySQL\u5728\u8ba1\u7b97index merge\u7684\u6210\u672c\u65f6\uff0c\u5206\u5f00\u8003\u8651\u4e86ROR\u548cnon-ROR\u7684\u573a\u666f\u3002\u6240\u4ee5\u8fd9\u91cc\u5148\u5355\u72ec\u4ecb\u7ecd\u4e00\u4e0b\u4ec0\u4e48\u662fROR\uff0c\u540e\u9762\u518d\u4ecb\u7ecdMySQL\u5982\u4f55\u533a\u522b\u5bf9\u5f85ROR\u7684\u6210\u672c\u8ba1\u7b97\u3002<\/p>\n<h4>4.1 \u4ec0\u4e48\u662fRowid-Ordered Retrieval<\/h4>\n<p>Rowid-Ordered Retrieval\u7b80\u79f0ROR\u3002\u770b\u4e0b\u9762\u7684\u8bf4\u660e\u3002\u6709\u57fa\u4e8e\u7d22\u5f15\u7684\u67e5\u8be2\uff1a<\/p>\n<blockquote><p>&#8220;key_1=c_1 AND &#8230; AND key_n=c_n&#8221;<\/p><\/blockquote>\n<p>\u8be5\u7d22\u5f15\u5b9a\u4e49\u4e3a\uff1a(key_1, &#8230;, key_N [,a_1, &#8230;, a_m])\uff0c\u4e14\u4e3b\u952e\u5217\u4e3a(a_1, &#8230;, a_m, b1, &#8230;, b_k)\uff0c\u5e76\u4e14n >= N\u3002<\/p>\n<p>\u90a3\u4e48\u8fd9\u4e2a\u67e5\u8be2\u5c31\u662f\u4e00\u4e2aROR\u67e5\u8be2\u3002\u7b80\u5355\u8bf4\u660e\uff1a\u5bf9\u4e8e\u8be5\u7d22\u5f15\u5de6\u524d\u7f00(key_1,&#8230;key_n)\u90fd\u662f\u5b9a\u503c\uff0c\u5bf9\u5e94\u8be5\u503c\u7684\u5b50\u6811\u987a\u5e8f\u662f\u6309\u7167\u5269\u4f59\u7d22\u5f15\u5217\u6765\u6392\u5e8f\u7684\uff0c\u800c\u5269\u4f59\u7684\u7d22\u5f15\u5217\u53c8\u90fd\u662f\u4e3b\u952e\u6700\u5de6\u524d\u7f00\uff0c\u6240\u4ee5\u5b50\u6811\u7684\u987a\u5e8f\u6070\u597d\u540c\u4e3b\u952e\u987a\u5e8f\u76f8\u540c\u3002<\/p>\n<p>(\u8fd9\u4e00\u6bb5\u53ef\u4ee5\u53c2\u8003\u51fd\u6570is_key_scan_ror\u7684\u6ce8\u91ca\u548c\u5b9e\u73b0\u90e8\u5206)<\/p>\n<p>\u793a\u4f8b\uff1a<\/p>\n<pre><div class=\"mycode\">CREATE TABLE `tmp_index_merge` (\r\n  `id` int(11) NOT NULL,\r\n  `key1_part1` int(11) NOT NULL,\r\n  `key1_part2` int(11) NOT NULL,\r\n  `key2_part1` int(11) NOT NULL,\r\n  `key2_part2` int(11) NOT NULL,\r\n  `key2_part3` int(11) NOT NULL,\r\n  `key3_part1` int(11) NOT NULL DEFAULT '4',\r\n  PRIMARY KEY (`id`),\r\n  KEY `ind2` (`key2_part1`,`key2_part2`,`key2_part3`),\r\n  KEY `ind1` (`key1_part1`,`key1_part2`,`id`),\r\n  KEY `ind3` (`key3_part1`,`id`)\r\n) ENGINE=InnoDB;\r\n\r\nexplain select * from tmp_index_merge where (key1_part1 = 4333 and key1_part2 = 1657) or (key3_part1 = 2877);\r\nj+----+-------------+-----------------+-------------+---------------+-----------+---------+------+------+-------------------------------------+\r\n| id | select_type | table           | type        | possible_keys | key       | key_len | ref  | rows | Extra                               |\r\n+----+-------------+-----------------+-------------+---------------+-----------+---------+------+------+-------------------------------------+\r\n|  1 | SIMPLE      | tmp_index_merge | index_merge | ind1,ind3     | ind1,ind3 | 8,4     | NULL |    2 | Using union(ind1,ind3); Using where |\r\n+----+-------------+-----------------+-------------+---------------+-----------+---------+------+------+-------------------------------------+\r\n\r\n\u8fd9\u5c31\u662f\u4e00\u4e2aROR\u7684index\u67e5\u8be2\u3002ROR\u5728Explain\u7684\u6267\u884c\u8ba1\u5212\u4e2d\u5e76\u6ca1\u6709\u4efb\u4f55\u4f53\u73b0\uff0c\u901a\u8fc7\u5728\u4ee3\u7801\u4e2d\u8bbe\u7f6e\u65ad\u70b9\u53ef\u4ee5\u89c2\u5bdf\u5230\u3002\u5728\u51fd\u6570get_best_disjunct_quick\u4e2d\uff0c\u4ee3\u7801\u4f1a\u8df3\u5230\u6807\u7b7eskip_to_ror_scan\u5904\u6267\u884c\u3002\r\n\r\n<\/div><\/pre>\n<p>\u5728\u5bf9index merge\u7684\u6210\u672c\u8bc4\u4f30\u65f6\uff0c\u53ea\u6709\u6240\u6709\u7684SEL_TREE\u5b50\u6811\u90fd\u662fROR\u7684\uff0c\u5bf9\u5e94\u7684SEL_IMERGE\u624d\u662fROR\u7684\u3002\u540e\u9762\u6211\u4eec\u5c06\u770b\u770bROR\u548cnon-ROR\u5728\u6210\u672c\u8bc4\u4f30\u4e0a\u7684\u4e0d\u540c\u3002<\/p>\n<h4>4.2 \u6210\u672c\u6982\u8ff0<\/h4>\n<p>\u4e00\u4e2aindex merge\u662f\u7531\u591a\u4e2aSEL_TREE\u5b50\u6811\u7ec4\u6210\uff0c\u6bcf\u4e2aSEL_TREE\u5bf9\u5e94\u4e00\u4e2arange\u64cd\u4f5c(<a href=\"http:\/\/www.orczhou.com\/index.php\/2012\/11\/mysql-source-code-range-optimize-data-structure\/\" target=\"_blank\" rel=\"noopener\">\u53c2\u8003<\/a>)\uff0c\u6240\u4ee5\u6bcf\u4e2aSEL_TREE\u6210\u672c\u4ecd\u7136\u4f1a\u6309\u7167range\u64cd\u4f5c\u7c7b\u4f3c\u5404\u81ea\u8ba1\u7b97\u6210\u672c\uff0c\u5e76\u7d2f\u52a0\u3002<\/p>\n<p>\u5404\u4e2aSEL_TREE\u5b50\u6811\u5404\u81ea\u83b7\u53d6ROWIDs\u540e\uff0cMySQL\u9700\u8981\u5bf9\u8fd9\u4e9bROWID\u8fdb\u884c\u53bb\u91cd\uff0c\u6700\u540e\u6839\u636eROWID\u83b7\u53d6\u6240\u6709\u6570\u636e\u3002\u53bb\u91cd\u64cd\u4f5c\u5176\u5b9e\u662f\u4e00\u4e2a\u5bf9\u591a\u7ec4ROWID\u5f52\u5e76\u6392\u5e8f\u7684\u95ee\u9898\u3002\u5bf9\u4e8eROR\u548cnon-ROR\u573a\u666f\u5f52\u5e76\u6392\u5e8f\u590d\u6742\u5ea6\u7565\u6709\u4e0d\u540c\u3002\u5bf9\u4e8enon-ROR\u7684\u573a\u666f\uff0c\u9700\u8981\u5148\u8fdb\u884c\u5206\u7ec4\u6392\u5e8f\uff0c\u7136\u540e\u5408\u5e76\u3002\u800c\u5bf9\u4e8eROR\uff0c\u56e0\u4e3aROWID\u662f\u987a\u5e8f\u7684\uff0c\u6240\u4ee5\u524d\u9762\u7684\u5206\u7ec4\u6392\u5e8f\u5c31\u7701\u7565\u4e86\uff0c\u76f4\u63a5\u505a\u5408\u5e76\u64cd\u4f5c\uff0c\u8fd9\u8ba9non-ROR\u548cROR\u5728\u6210\u672c\u8ba1\u7b97\u4e0a\u6709\u8f83\u5927\u7684\u4e0d\u540c\u3002<\/p>\n<p>\u5728\u5b8c\u6210\u53bb\u91cd\u4e4b\u540e\uff0c\u6700\u540e\u662f\u6839\u636eROWID\u53d6\u51fa\u4e3b\u952e\u7684\u6210\u672c(\u5bf9\u5e94\u7684\u4e8c\u7ea7\u7d22\u5f15\u91cc\u9762\u53d6\u51fa\u7684ROWID)\u3002<\/p>\n<p>\u4e00\u4e2a\u7ec6\u8282\uff1a\u5982\u679c\u67d0\u4e2aSEL_TREE\u5bf9\u5e94\u7684\u7d22\u5f15\u6070\u597d\u662f\u4e3b\u952e\u7d22\u5f15\u65f6\uff0c\u90a3\u4e48MySQL\u4f1a\u5728\u5176\u4ed6SEL_TREE\u5b50\u6811\u626b\u63cf\u65f6\uff0c\u76f4\u63a5\u5224\u65ad\u626b\u63cf\u51fa\u6765\u7684ROWID\u662f\u5426\u5728\u4e3b\u952e\u5bf9\u5e94\u7684SEL_TREE\u7684range\u5185\uff0c\u5982\u679c\u8fd9\u4e2aROWID\u5df2\u7ecf\u5b58\u5728\uff0c\u5219\u4e0d\u5728\u8bb0\u5f55\u3002\u8fd9\u6837\u53ef\u4ee5\u5c3d\u53ef\u80fd\u7684\u51cf\u5c11\u5f52\u5e76\u6392\u5e8f\u7684\u5143\u7d20\u4e2a\u6570\u3002\u6211\u4eec\u79f0\u8fd9\u90e8\u5206\u6210\u672c\u5473&#8221;<b>\u4e8c\u7ea7ROWID\u8fc7\u6ee4\u6210\u672c<\/b>&#8220;\u3002<\/p>\n<h4>4.3 SEL_TREE\u5b50\u6811\u7684\u6210\u672c<\/h4>\n<p>\u8fd9\u90e8\u5206\u6210\u672c\u8ba1\u7b97\u4e0erange\u6210\u672c\u8ba1\u7b97\u76f8\u540c(<a href=\"http:\/\/www.orczhou.com\/index.php\/2012\/11\/mysql-source-code-range-optimize-data-structure\/\" target=\"_blank\" rel=\"noopener\">\u53c2\u8003<\/a>)\uff0c\u8fd9\u91cc\u4f1a\u5c06\u591a\u4e2a\u5b50\u6811\u6210\u672c\u5355\u72ec\u8ba1\u7b97\u5e76\u7d2f\u52a0\u3002<\/p>\n<pre><blockquote>for (every SEL_TREE IN SEL_IMERGE){\r\n  cur_child= get_key_scans_params(param, *ptree, TRUE, FALSE, read_time);\r\n  imerge_cost += (*cur_child)->read_cost;\r\n  ......\r\n}<\/blockquote><\/pre>\n<h4>4.4 non-ROR\u573a\u666f\u7684\u6210\u672c\u8ba1\u7b97<\/h4>\n<p>\u8fd9\u91cc\u901a\u8fc7\u6392\u5e8f\u8fdb\u884c\u53bb\u91cd\uff0c\u662f\u5178\u578b\u7684\u5f52\u5e76\u6392\u5e8f\uff0c\u5982\u679c\u8d85\u8fc7MySQL\u6392\u5e8f\u5185\u5b58\u7684\u9650\u5236\uff0c\u5219\u662f\u5178\u578b\u7684\u5916\u6392\u5e8f\u3002\u5148\u5206\u7ec4\u505a\u7ea2\u9ed1\u6811\u6392\u5e8f\uff0c\u7136\u540e\u8fdb\u884c\u5408\u5e76\u3002\u6210\u672c\u5206\u4e3a\u51e0\u90e8\u5206\uff1a\u521b\u5efa\u7ea2\u9ed1\u6811\u3001\u5916\u6392\u65f6\u78c1\u76d8\u8bfb\u5199\u3001\u6700\u540e\u987a\u5e8f\u8bfb\u53d6\u6392\u5e8f\u7ed3\u679c\u3002<\/p>\n<h5>4.4.1 \u53bb\u91cd\u590d\u6210\u672c\u8ba1\u7b97\u6982\u8ff0<\/h5>\n<p>\u8fd9\u90e8\u5206\u7684\u6210\u672c\u53ef\u4ee5\u5b8c\u6574\u7684\u53c2\u8003\u51fd\u6570Unique::get_use_cost\uff0c\u8fd9\u91cc\u505a\u4e00\u4e2a\u8f83\u4e3a\u8be6\u7ec6\u7684\u8865\u5145\u8bf4\u660e\u3002<\/p>\n<p>\u5bf9\u8fd9\u4e2a\u95ee\u9898\u505a\u4e00\u4e2a\u7b80\u5355\u7684\u62bd\u8c61\uff1a\u6709\u4e24\u90e8\u5206\u6570\u636e\uff0c\u7b2c\u4e00\u90e8\u5206\u6709cpk_scan_records\u6761\uff0c\u5df2\u6392\u5e8f\u3002\u7b2c\u4e8c\u90e8\u5206\u6709non_cpk_scan_records\u672a\u6392\u5e8f\uff0c\u73b0\u5728\u9700\u8981\u8fd4\u56de\u53bb\u91cd\u540e\u6240\u6709\u6570\u636e\u3002\u5355\u6761\u6570\u636e\u5927\u5c0f\u4e3akey_size\uff0c\u53ef\u7528\u5185\u5b58\u4e3amax_in_memory_size\u3002\u56e0\u4e3a\u524d\u9762\u5bf9\u7b2c\u4e8c\u90e8\u6570\u636e\u505a\u4e86&#8221;\u4e8c\u7ea7ROWID\u8fc7\u6ee4&#8221;\uff0c\u6240\u4ee5\u8fd9\u90e8\u5206ROWID\u8ddf\u7b2c\u4e00\u90e8\u5206\u6ca1\u6709\u91cd\u590d\u3002\u56e0\u6b64\uff0c\u4ec5\u8fd9\u91cc\u7684\u7b2c\u4e8c\u90e8\u5206\u6570\u636e\u9700\u8981\u8fdb\u884c\u53bb\u91cd\u3002\u53bb\u91cd\u901a\u8fc7\u4e00\u4e2a\u6392\u5e8f\u5b9e\u73b0\u3002<\/p>\n<p>\u7b80\u5355\u7684\u8bf4\uff0c\u9700\u8981\u5bf9non_cpk_scan_records\u6761\u8bb0\u5f55\u8fdb\u884c\u5916\u6392\u5e8f\uff0c\u6700\u5927\u53ef\u7528\u5185\u5b58\u662fmax_in_memory_size\uff0c\u5355\u6761\u8bb0\u5f55\u5927\u5c0f\u662fkey_size\u3002\u6392\u5e8f\u5206\u6210\u4e24\u90e8\u5206\uff0c\u5bf9\u90e8\u5206\u6570\u636e\u505a\u6392\u5e8f\uff0c\u7136\u540e\u5408\u5e76\u3002<\/p>\n<h5>4.4.2 \u4e8c\u7ea7ROWID\u8fc7\u6ee4\u6210\u672c<\/h5>\n<p>\u5982\u679c\u6709\u5b50\u6811SEL_TREE\u662f\u5bf9\u5e94\u4e3b\u952e\u805a\u7c07\u7d22\u5f15\uff0c\u53e6\u4e00\u90e8\u5206\u5b50\u6811SEL_TREE\u5bf9\u5e94\u4e8c\u7ea7\u7d22\u5f15\uff0c\u90a3\u4e48\u5728\u904d\u5386\u4e8c\u7ea7\u7d22\u5f15\u65f6\u5c06\u53d6\u51fa\u5bf9\u5e94\u7684ROWID\uff0c\u770b\u770b\u662f\u5426\u518d\u805a\u7c07\u7d22\u5f15\u7684SEL_TREE\u5b50\u6811\u4e2d\uff0c\u5982\u679c\u662f\uff0c\u90a3\u4e48\u53ef\u4ee5\u5ffd\u7565\u8fd9\u4e2aROWID\uff0c\u4ee5\u514d\u91cd\u590d\u8ba1\u7b97(\u51cf\u5c11\u540e\u9762Unique\u64cd\u4f5c)\u3002\u8fd9\u90e8\u5206\u7684\u6210\u672c\u8ba1\u7b97\u4e3a\uff1a<\/p>\n<pre><blockquote>imerge_cost += non_cpk_scan_records \/ TIME_FOR_COMPARE_ROWID;<\/blockquote><\/pre>\n<p>\u53e6\u5916\uff0c\u8fd9\u91cc\u8bb0cpk_scan_records\u4e3a\u4e3b\u952e\u805a\u7c07\u7d22\u5f15\u5bf9\u5e94\u7684SEL_TREE\u8fd4\u56de\u7684ROWID\u6570\u91cf\uff0cnon_cpk_scan_records\u4e3a\u4e8c\u7ea7\u7d22\u5f15\u5bf9\u5e94\u7684\u6240\u6709SEL_TREE\u8fd4\u56de\u7684ROWID\u6570\u91cf\u3002<\/p>\n<h5>4.4.3 \u6392\u5e8f\u6bd4\u8f83\u6210\u672c<\/h5>\n<p>\u9700\u8981\u8fdb\u884cN=non_cpk_scan_records*key_size\/max_in_memory_size\u6b21\u6392\u5e8f\u3002\u5728\u6bcf\u6b21\u6392\u5e8f\u8fc7\u7a0b\u4e2d\uff0c\u5982\u679c\u5df2\u7ecf\u6392\u5e8f\u597d\u7684\u8bb0\u5f55\u6811m\u4e2a\uff0c\u90a3\u4e48\u65b0\u589e\u4e00\u6761\u8bb0\u5f55\u5e73\u5747\u9700\u8981\u505alog2(m+1)\u6b21\u6bd4\u8f83\u64cd\u4f5c\uff0cm\u53d6\u503c\u662f\u4ece1,2&#8230;N\u3002\u6bd4\u8f83\u64cd\u4f5c\u7684\u6210\u672c\u4e3alog2((m+1)!)\uff0cMySQL\u4f7f\u7528\u4e86\u5982\u4e0b\u516c\u5f0f\u8ba1\u7b97log2((m+1)!)\uff1a<\/p>\n\n<p>\\[n! \\approx \\sqrt{2{\\pi}n}(\\frac{n}{e})^n\\]<\/p>\n<p>\\[\\log{n!} \\approx \\log{\\sqrt{2{\\pi}n}} + n*\\log{\\frac{n}{e}} \\]  <\/p>\n<p>\u8fd9\u91cclog\u662f2\u4e3a\u5e95\u6570\uff0c\u518d\u4f7f\u7528\\[log_{n}{m} = \\frac{\\lg{n}}{\\lg{m}}\\] \u901a\u8fc7\u6b64\u516c\u5f0f\u5e95\u6570\u90fd\u53ef\u4ee5\u8f6c\u6362\u4e3a10\u8fdb\u884c\u8fd0\u7b97(\u8fd9\u4e00\u90e8\u5e76\u4e0d\u662f\u5fc5\u987b\u7684\uff0c\u4e0d\u8fc7MySQL\u662f\u8fd9\u6837\u8ba1\u7b97\u7684)\u3002<\/p>\n<p>\u9636\u4e58\u8f6c\u6362\u53c2\u8003\uff1a<a href=\"http:\/\/zh.wikipedia.org\/wiki\/%E6%96%AF%E7%89%B9%E9%9D%88%E5%85%AC%E5%BC%8F\" target=\"_blank\" rel=\"noopener\">\u65af\u7279\u9748\u516c\u5f0f<\/a>(\u53e3\u5473\u7565\u91cd\uff0c\u614e\u5165)\u3002<\/p>\n<p>\u5bf9\u5e94\u7684\u4ee3\u7801\u6bb5\uff1a<\/p>\n<blockquote><p>result+= n_full_trees * log2_n_fact(max_elements_in_tree + 1.0);<br \/>\nresult \/= TIME_FOR_COMPARE_ROWID;<\/p><\/blockquote>\n<h5>4.4.4 \u5916\u6392\u5e8f\u65f6\u5019\u7684\u78c1\u76d8IO\u6210\u672c<\/h5>\n<p>\u5728\u5916\u6392\u7684\u65f6\u5019\uff0c\u9700\u8981\u5bf9\u6240\u6709\u7684\u6570\u636e\u8fdb\u884c\u4e00\u6b21IO\u64cd\u4f5c\uff0c\u6210\u672c\u8ba1\u7b97\u5982\u4e0b\uff1a<\/p>\n<blockquote><p>293   result += DISK_SEEK_BASE_COST * n_full_trees * max_elements_in_tree \/ IO_SIZE;<br \/>\n295   result += DISK_SEEK_BASE_COST * key_size * last_tree_elems \/ IO_SIZE;<\/p><\/blockquote>\n<p>\u7b2c\u4e00\u884c\u662f\u5b8c\u6574\u6811\u7684IO\u6210\u672c\uff0c\u7b2c\u4e8c\u90e8\u5206\u662f\u6700\u540e\u4e00\u4e2a\u53ef\u80fd\u4e0d\u5b8c\u6574\u6811\u7684IO\u6210\u672c\u3002<\/p>\n<h5>4.4.5 \u5408\u5e76\u6210\u672c<\/h5>\n<p>\u6700\u540e\u662f\u5408\u5e76\u6210\u672c\uff0c\u8fd9\u662f\u4e00\u4e2a\u5178\u578b\u7684\u5f52\u5e76\u6392\u5e8f\uff0c\u662f\u5bf9K\u4e2a<b>\u6709\u5e8f<\/b>\u5217\u8868\u8fdb\u884c\u5f52\u5e76\uff0c\u65f6\u95f4\u590d\u6742\u5ea6\u4e3a\uff1a<\/p>\n<p>\\[O(N*\\lg{K})\\]<\/p>\n<p>\u5f52\u5e76\u8fc7\u7a0b\u4e2d\u6709\u4e00\u6b21\u8bfb\u5199\u64cd\u4f5c\uff0cIO\u548c\u6bd4\u8f83\u6210\u672c\u52a0\u8d77\u6765\u5c31\u662f\u5408\u5e76\u7684\u6210\u672c\uff1a<\/p>\n<p>\\[\\frac{total\\_buf\\_elems*\\log(n\\_buffers)}{TIME\\_FOR\\_COMPARE\\_ROWID*\\log2} + 2*\\frac{total\\_buf\\_elems*elem\\_size}{IO\\_SIZE} \\]<\/p>\n<p>total_buf_elems\u662f\u603b\u5143\u7d20\u4e2a\u6570\uff1bn_buffers\u5b50\u6811\u6570\u91cf\uff1belem_size\u4e3a\u5355\u4e2a\u5143\u7d20\u5927\u5c0f\u3002<\/p>\n<p>\u672a\u5c3d\u7684\u7ec6\u8282\uff1aMySQL\u4e00\u6b21\u6700\u591a\u5bf915(MERGEBUFF2)\u9897\u5b50\u6811\u505a\u5f52\u5e76\u3002<\/p>\n<h5>4.4.6 \u6700\u540e\u7684\u8bfb\u53d6<\/h5>\n<p>\u8fd9\u65f6\uff0c\u5b8c\u6210\u4e86\u6240\u6709\u7684\u6392\u5e8f\u64cd\u4f5c\uff0c\u6700\u540e\u662f\u8bfb\u53d6\u7ed3\u679c\u5230\u5185\u5b58\u7684\u6210\u672c\uff1a<\/p>\n<p>result += ceil((double)key_size*nkeys\/IO_SIZE);<\/p>\n<h5>4.4.7 \u6839\u636eROWID\u53d6\u51fa\u8bb0\u5f55\u7684\u6210\u672c<\/h5>\n<p>\u6240\u6709\u975e\u805a\u7c07\u7d22\u5f15\u626b\u63cf\u83b7\u5f97ROWID\u540e\uff0c\u6700\u540e\u4ecd\u7136\u9700\u8981\u6839\u636e\u8fd9\u4e9bROWID\u83b7\u53d6\u8bb0\u5f55\u3002<\/p>\n<p>\u5bf9\u4e8e\u7d22\u5f15\u7ec4\u7ec7\u8868(\u805a\u7c07\u7d22\u5f15\uff0cInnoDB)\uff0c\u8fd9\u90e8\u5206\u7684\u6210\u672c\u8ba1\u7b97\u8f83\u4e3a\u7b80\u5355\uff0c\u5047\u8bbe\u805a\u7c07\u7d22\u5f15\u7684\u603bpage\u4e3atotal_pages\uff0c\u8fd9\u91cc\u4e8c\u7ea7\u7d22\u5f15\u53d6\u51fa\u7684rowid\u6570\u91cf\u4e3arows\uff0c\u8be5\u8868\u7684\u603b\u8bb0\u5f55\u6811\u4e3atotal_rows\uff0c\u90a3\u4e48\u6210\u672c\u4e3a\uff1a<\/p>\n<p>(rows \/ total_rows) *total_pages<\/p>\n<p>\u4ee3\u7801\u53c2\u8003\uff1a<\/p>\n<blockquote><p>imerge_cost += get_sweep_read_cost(param, non_cpk_scan_records);<\/p><\/blockquote>\n<h4>4.5 ROR\u573a\u666f\u7684\u6210\u672c\u8ba1\u7b97<\/h4>\n<p>ROR\u7684\u65f6\u5019\uff0c\u53bb\u91cd\u65f6\u5219\u5c11\u4e86\u5bf9\u5b50\u961f\u5217\u7684\u6392\u5e8f\uff0c\u76f4\u63a5\u662f\u5bf9\u591a\u4e2a\u5df2\u7ecf\u6392\u5217\u597d\u7684\u961f\u5217\u505a\u5408\u5e76\u6392\u5e8f\u3002\u6240\u4ee5\u8fd9\u91cc\u7684\u6210\u672c\u8ba1\u7b97\u76f8\u5bf9\u7b80\u5355\uff1a\u7d22\u5f15\u8bfb\u53d6\uff0c\u5408\u5e76\u6392\u5e8f\uff0c\u6700\u540e\u662f\u6839\u636eROWID\u53d6\u51fa\u6240\u6709\u8bb0\u5f55\u7684\u6210\u672c\u3002<\/p>\n<h5>4.5.1 \u7d22\u5f15\u8bfb\u53d6\u6210\u672c<\/h5>\n<p>\u8fd9\u90e8\u5206\u8ba1\u7b97\u4e0e\u7d22\u5f15\u8986\u76d6\u626b\u63cf\u8ba1\u7b97\u76f8\u540c\u3002\u5047\u8bbe\u5355\u4e2a\u7d22\u5f15\u5757\u5927\u5c0f\u4e3aBS\uff0c\u7d22\u5f15\u5b57\u6bb5\u957f\u5ea6\u5473KL\uff0cROWID\u957f\u5ea6\u4e3aRL\uff0c\u603b\u662f\u5047\u8bbe\u7d22\u5f15\u5757\u670950%\u4e3a\u7a7a\uff0c\u5982\u679c\u9700\u8981\u626b\u63cf\u7684\u8bb0\u5f55\u6570\u4e3aRS\uff0c\u90a3\u4e48\u8fd9\u90e8\u5206\u6210\u672c\u8ba1\u7b97\u4e3a\uff1a<\/p>\n<p>\\[\\frac{RS}{\\frac{1}{2}\\frac{BS}{(KL+RL)}}\\]<\/p>\n<p>\u53c2\u8003\u51fd\u6570get_index_only_read_time\u7684\u5b9e\u73b0\u3002<\/p>\n<h5>4.5.2 \u5408\u5e76\u6392\u5e8f<\/h5>\n<p>\u8fd9\u6b21\u5408\u5e76\u6392\u5e8f\uff0c\u662f\u5bf9\u591a\u4e2a\u6709\u5e8f\u5217\u8868\u7684\u5408\u5e76\u3002\u82e5\u6709K\u4e2a\u6709\u5e8f\u5217\u8868\uff0c\u603b\u8bb0\u5f55\u6570\u5473N\uff0c\u90a3\u4e48\u5176\u6210\u672c\u4e3a\uff1a<\/p>\n<p>\\[O(N*\\lg{K})\\]<\/p>\n<p>\u8fd9\u91ccN\u4e3a\u5404\u4e2aSEL_TREE\u5b50\u6811\u5bf9\u5e94found_records\u4e4b\u548c(MySQL\u8fd9\u91cc\u7684\u8ba1\u7b97\u7565\u5fae\u4e0d\u540c)\u3002<\/p>\n<h5>4.5.3 \u6839\u636eROWID\u53d6\u51fa\u8bb0\u5f55\u7684\u6210\u672c<\/h5>\n<p>\u8fd9\u90e8\u5206\u6210\u672c\u4e8eNON-ROR\u573a\u666f\u76f8\u540c\uff0c\u5bf9\u4e8e\u7d22\u5f15\u7ec4\u7ec7\u8868(\u805a\u7c07\u7d22\u5f15\uff0cInnoDB)\uff0c\u8fd9\u90e8\u5206\u7684\u6210\u672c\u8ba1\u7b97\u8f83\u4e3a\u7b80\u5355\uff0c\u5047\u8bbe\u805a\u7c07\u7d22\u5f15\u7684\u603bpage\u4e3atotal_pages\uff0c\u8fd9\u91cc\u4e8c\u7ea7\u7d22\u5f15\u53d6\u51fa\u7684rowid\u6570\u91cf\u4e3arows\uff0c\u8be5\u8868\u7684\u603b\u8bb0\u5f55\u6811\u4e3atotal_rows\uff0c\u90a3\u4e48\u6210\u672c\u4e3a\uff1a<\/p>\n<p>(rows \/ total_rows) *total_pages<\/p>\n<p>\u5728MySQL\u4e2d\uff0c\u5bf9\u4e8e\u4e0a\u9762\u8868\u8fbe\u5f0f\u7684rows\u8ba1\u7b97\u505a\u4e86\u4e00\u4e9b\u4e0d\u4e00\u6837\u7684\u5904\u7406\u3002\u8fd9\u91cc\u8bf4\u4e00\u4e0b\u4e3b\u8981\u601d\u60f3\uff0cMySQL\u5047\u8bbe\u6bcf\u4e2aSEL_TREE\u5b8c\u5168\u72ec\u7acb\uff0c\u603b\u8bb0\u5f55\u6570\u5473R\uff0c\u5982\u679c\u6709\u4e09\u4e2aSEL_TREE\u5b50\u6811\uff0c\u8bb0\u5bf9\u5e94\u7684\u8bb0\u5f55\u6570\u4e3aR(1),R(2),R(3)\u3002<strong>\u5982\u679c\u6570\u636e\u90fd\u5747\u5300\u5206\u5e03<\/strong>\uff0c\u90a3\u4e48\u53bb\u91cd\u540e\u603b\u8bb0\u5f55\u6570\u4e3a\uff1a<\/p>\n<blockquote><p>(R(1)+R(2)+R(3)) &#8211; R(a)*(R(1)*R(2)+R(2)+R(3)+R(1)*R(3))\/R(a)^2 + R(a)*((R(1)*R(2)*R3)\/R(a)^3)<\/p><\/blockquote>\n<p>MySQL\u8fd9\u91cc\u505a\u4e86\u4e00\u4e2a\u8fd1\u4f3c\uff1a<\/p>\n<blockquote><p>(R(1)+R(2)+R(3)) &#8211; R(a)*((R(1)*R(2)*R3)\/R(a)^3)<\/p><\/blockquote>\n<p>MySQL\u5229\u7528\u8fd9\u4e2a\u8fd1\u4f3c\u503c\u4f5c\u4e3a\u4e0a\u9762\u516c\u5f0f\u7684rows\u3002\u5230\u8fd9\u91ccROR\u90e8\u5206\u6210\u672c\u5c31\u5b8c\u6210\u4e86\u3002<\/p>\n<h3>5 \u6700\u540e<\/h3>\n<p>\u6700\u540e\uff0c\u5982\u679cindex merge\u7684\u6210\u672c\u6bd4\u5176\u4ed6\u6267\u884c\u8ba1\u5212\u7684\u6210\u672c\u8981\u66f4\u5c0f\u7684\u8bdd\uff0c\u90a3\u4e48MySQL\u5c31\u4f1a\u9009\u62e9\u6539\u6267\u884c\u8ba1\u5212\u3002\u6848\u4f8b\u53ef\u4ee5\u53c2\u8003<a href=\"http:\/\/www.orczhou.com\/index.php\/2013\/01\/mysql-source-code-query-optimization-index-merge\/\" target=\"_blank\" rel=\"noopener\">index merge\u4ecb\u7ecd<\/a>\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u524d\u9762\u4ee5\u6848\u4f8b\u7684\u5f62\u5f0f\u4ecb\u7ecd\u4e86\u4ec0\u4e48\u662findex merge\uff0c\u4ee5\u53ca\u5b83\u7684\u4f7f\u7528\u573a\u666f\u3002\u672c\u6587\u5c06\u4ecb\u7ecdindex merge\u5b9e\u73b0\u7684\u4e3b\u8981\u6570\u636e\u7ed3\u6784\u4ee5\u53caMySQL\u5982\u4f55\u8bc4\u4f30index 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