{"id":2091,"date":"2023-04-01T21:58:13","date_gmt":"2023-04-01T13:58:13","guid":{"rendered":"https:\/\/www.appblog.cn\/?p=2091"},"modified":"2023-04-06T14:48:06","modified_gmt":"2023-04-06T06:48:06","slug":"why-dont-sql-statements-have-too-many-joins","status":"publish","type":"post","link":"https:\/\/www.appblog.cn\/index.php\/2023\/04\/01\/why-dont-sql-statements-have-too-many-joins\/","title":{"rendered":"\u4e3a\u4ec0\u4e48 SQL \u8bed\u53e5\u4e0d\u8981\u8fc7\u591a\u7684 join\uff1f"},"content":{"rendered":"<h2>free\u547d\u4ee4\u7f13\u5b58buff\/cache<\/h2>\n<p>\u67e5\u770b\u5185\u5b58\u7684\u547d\u4ee4\uff1afree \u6216\u8005 top\uff0c\u5176\u4e2d\u4f7f\u7528free\u547d\u4ee4\u90fd\u53ef\u4ee5\u770b\u5230\u4fe1\u606f<\/p>\n<pre><code class=\"language-bash\">$ free -mh\n              total        used        free      shared  buff\/cache   available\nMem:           2.0G        516M        677M         23M        806M        1.2G\nSwap:            0B          0B          0B<\/code><\/pre>\n<p><!-- more --><\/p>\n<ul>\n<li>total \u603b\u5185\u5b58<\/li>\n<li>used \u5df2\u7528\u5185\u5b58<\/li>\n<li>free \u7a7a\u95f2\u5185\u5b58<\/li>\n<li>buff\/cache \u5df2\u4f7f\u7528\u7684\u7f13\u5b58<\/li>\n<li>avaiable \u53ef\u7528\u5185\u5b58<\/li>\n<\/ul>\n<p>\u6e05\u7406\u5df2\u4f7f\u7528\u7684\u7f13\u5b58(buff\/cache)\uff1a<\/p>\n<pre><code>sync; echo 3 &gt; \/proc\/sys\/vm\/drop_caches<\/code><\/pre>\n<p>\u4f46\u662f\u6ce8\u610f\u5728\u7ebf\u4e0a\u5207\u52ff\u6267\u884c\u8fd9\u6761\u547d\u4ee4\uff0c\u539f\u56e0\u4e4b\u4e00\u53ef\u4ee5\u901a\u8fc7 MySQL \u7684 join\u6307\u4ee4\u8bf4\u660e<\/p>\n<h2>SQL Join<\/h2>\n<p>SQL\u4e2d\u7684join\u53ef\u4ee5\u6839\u636e\u67d0\u4e9b\u6761\u4ef6\u628a\u6307\u5b9a\u7684\u8868\u7ed9\u7ed3\u5408\u8d77\u6765\u5e76\u5c06\u6570\u636e\u8fd4\u56de<\/p>\n<p>join\u7684\u65b9\u5f0f\u6709\uff1a5 \u79cd <\/p>\n<ul>\n<li>inner join \u5185\u8fde\u63a5<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"http:\/\/www.yezhou.me\/AppBlog\/images\/\u6570\u636e\u5e93\/MySQL-inner%20join%20\u5185\u8fde\u63a5.png\" alt=\"MySQL-inner join \u5185\u8fde\u63a5\" \/><\/p>\n<ul>\n<li>left join \u5de6\u8fde\u63a5<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"http:\/\/www.yezhou.me\/AppBlog\/images\/\u6570\u636e\u5e93\/MySQL-left%20join%20\u5de6\u8fde\u63a5.png\" alt=\"MySQL-left join \u5de6\u8fde\u63a5\" \/><\/p>\n<ul>\n<li>right join \u53f3\u8fde\u63a5<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"http:\/\/www.yezhou.me\/AppBlog\/images\/\u6570\u636e\u5e93\/MySQL-right%20join%20\u53f3\u8fde\u63a5.png\" alt=\"MySQL-right join \u53f3\u8fde\u63a5\" \/><\/p>\n<ul>\n<li>full join \u5168\u8fde\u63a5<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"http:\/\/www.yezhou.me\/AppBlog\/images\/\u6570\u636e\u5e93\/MySQL-full%20join%20\u5168\u8fde\u63a5.png\" alt=\"MySQL-full join \u5168\u8fde\u63a5\" \/><\/p>\n<p>\u5728\u9879\u76ee\u5f00\u53d1\u4e2d\u5982\u679c\u9700\u8981\u4f7f\u7528join\u8bed\u53e5\uff0c\u5982\u4f55\u4f18\u5316\u63d0\u5347\u6027\u80fd?<\/p>\n<ul>\n<li>\u6570\u636e\u89c4\u6a21\u8f83\u5c0f\uff1a\u53ef\u5168\u90e8\u585e\u8fdb\u5185\u5b58<\/li>\n<li>\u6570\u636e\u89c4\u6a21\u8f83\u5927\uff1a\u53ef\u4ee5\u901a\u8fc7\u589e\u52a0\u7d22\u5f15\u6765\u4f18\u5316join\u8bed\u53e5\u7684\u6267\u884c\u901f\u5ea6\uff0c\u53ef\u4ee5\u901a\u8fc7\u5197\u4f59\u4fe1\u606f\u6765\u51cf\u5c11join\u7684\u6b21\u6570\uff0c\u5c3d\u91cf\u51cf\u5c11\u8868\u8fde\u63a5\u7684\u6b21\u6570\uff0c\u4e00\u4e2aSQL\u8bed\u53e5\u8868\u8fde\u63a5\u7684\u6b21\u6570\u4e0d\u8981\u8d85\u8fc75\u6b21<\/li>\n<\/ul>\n<p>join\u8bed\u53e5\u662f\u76f8\u5bf9\u6bd4\u8f83\u8017\u8d39\u6027\u80fd\uff0c\u56e0\u4e3a\u5728\u6267\u884cjoin\u8bed\u53e5\u7684\u65f6\u5019\u5fc5\u7136\u8981\u6709\u4e00\u4e2a\u6bd4\u8f83\u7684\u8fc7\u7a0b\uff0c\u9010\u6761\u6bd4\u8f83\u4e24\u4e2a\u8868\u7684\u8bed\u53e5\u662f\u6bd4\u8f83\u6162\u7684\uff0c\u56e0\u6b64\u6211\u4eec\u53ef\u4ee5\u628a\u4e24\u4e2a\u8868\u4e2d\u6570\u636e\u4f9d\u6b21\u8bfb\u8fdb\u4e00\u4e2a\u5185\u5b58\u5757\u4e2d\uff0c\u4ee5MySQL\u7684InnoDB\u5f15\u64ce\u4e3a\u4f8b\uff0c\u4f7f\u7528\u8bed\u53e5<code>show variables like &#039;%buffer%&#039;<\/code>\u53ef\u4ee5\u67e5\u5230\u76f8\u5173\u7684\u5185\u5b58\u533a\u57df<\/p>\n<pre><code class=\"language-sql\">mysql&gt; show variables like &#039;%buffer%&#039;;\n+-------------------------------------+----------------+\n| Variable_name                       | Value          |\n+-------------------------------------+----------------+\n| bulk_insert_buffer_size             | 8388608        |\n| innodb_buffer_pool_dump_at_shutdown | OFF            |\n| innodb_buffer_pool_dump_now         | OFF            |\n| innodb_buffer_pool_filename         | ib_buffer_pool |\n| innodb_buffer_pool_instances        | 8              |\n| innodb_buffer_pool_load_abort       | OFF            |\n| innodb_buffer_pool_load_at_startup  | OFF            |\n| innodb_buffer_pool_load_now         | OFF            |\n| innodb_buffer_pool_size             | 134217728      |\n| innodb_change_buffer_max_size       | 25             |\n| innodb_change_buffering             | all            |\n| innodb_log_buffer_size              | 8388608        |\n| innodb_sort_buffer_size             | 1048576        |\n| join_buffer_size                    | 262144         |\n| key_buffer_size                     | 8388608        |\n| myisam_sort_buffer_size             | 8388608        |\n| net_buffer_length                   | 16384          |\n| preload_buffer_size                 | 32768          |\n| read_buffer_size                    | 131072         |\n| read_rnd_buffer_size                | 262144         |\n| sort_buffer_size                    | 262144         |\n| sql_buffer_result                   | OFF            |\n+-------------------------------------+----------------+\n22 rows in set (0.00 sec)<\/code><\/pre>\n<p>\u5176\u4e2d<code>join_buffer_size<\/code>\u7684\u5927\u5c0f\u5c06\u4f1a\u5f71\u54cd\u6211\u4eecjoin\u8bed\u53e5\u7684\u6267\u884c\u6027\u80fd<\/p>\n<p>\u5927\u90e8\u5206\u6570\u636e\u5e93\u4e2d\u7684\u6570\u636e\u6700\u7ec8\u8981\u4fdd\u5b58\u5230\u786c\u76d8\u4e0a\uff0c\u5e76\u4e14\u4ee5\u6587\u4ef6\u7684\u5f62\u5f0f\u8fdb\u884c\u5b58\u50a8\u3002\u4ee5MySQL\u7684InnoDB\u5f15\u64ce\u4e3a\u4f8b\uff1a<\/p>\n<ul>\n<li>InnoDB\u4ee5\u9875(page)\u4e3a\u57fa\u672c\u7684IO\u5355\u4f4d\uff0c\u6bcf\u4e2a\u9875\u7684\u5927\u5c0f\u4e3a16KB<\/li>\n<li>InnoDB\u4f1a\u4e3a\u6bcf\u4e2a\u8868\u521b\u5efa\u7528\u4e8e\u5b58\u50a8\u6570\u636e\u7684<code>.ibd<\/code>\u6587\u4ef6<\/li>\n<\/ul>\n<p>\u8fd9\u610f\u5473\u7740\u6211\u4eec\u6709\u591a\u5c11\u8868\u8981\u8fde\u63a5\u5c31\u9700\u8981\u8bfb\u591a\u5c11\u4e2a\u6587\u4ef6\uff0c\u867d\u7136\u53ef\u4ee5\u5229\u7528\u7d22\u5f15\uff0c\u4f46\u8fd8\u662f\u514d\u4e0d\u4e86\u9891\u7e41\u7684\u79fb\u52a8\u786c\u76d8\u7684\u78c1\u5934<\/p>\n<p>\u4e5f\u5c31\u662f\u8bf4\u9891\u7e41\u7684\u79fb\u52a8\u78c1\u5934\u4f1a\u5f71\u54cd\u6027\u80fd\uff0c\u73b0\u5728\u7684\u5f00\u6e90\u6846\u67b6\u90fd\u559c\u6b22\u8bf4\u81ea\u5df1\u901a\u8fc7\u987a\u5e8f\u8bfb\u5199\u5927\u5927\u7684\u63d0\u5347\u4e86\u6027\u80fd\uff0c\u6bd4\u5982hbase\u3001kafka<\/p>\n<p>\u90a3Linux\u6709\u5bf9\u6b64\u505a\u51fa\u4f18\u5316\u5417\uff1f\u518d\u6267\u884c\u4e00\u6b21free\u547d\u4ee4\u770b\u4e00\u4e0b<\/p>\n<pre><code class=\"language-bash\">$ free -m\n              total        used        free      shared  buff\/cache   available\nMem:           2.0G        610M        198M         23M        1.2G        1.1G\nSwap:            0B          0B          0B<\/code><\/pre>\n<p>\u5947\u602a\u7f13\u5b58\u600e\u4e48\u7adf\u7136\u5360\u75281.2G\u591a<\/p>\n<ul>\n<li><code>buff\/cache<\/code>\u91cc\u9762\u5b58\u7684\u662f\u4ec0\u4e48\uff1f<\/li>\n<li>\u4e3a\u4ec0\u4e48<code>buff\/cache<\/code>\u5360\u4e86\u90a3\u4e48\u591a\u5185\u5b58\uff0c\u53ef\u7528\u5185\u5b58\u5373<code>availlable<\/code>\u8fd8\u67091.1G\uff1f<\/li>\n<li>\u4e3a\u4ec0\u4e48\u53ef\u4ee5\u901a\u8fc7\u4e24\u6761\u547d\u4ee4\u6765\u6e05\u7406<code>buff\/cache<\/code>\u5360\u7528\u7684\u5185\u5b58\uff0c\u800c\u60f3\u8981\u91ca\u653e<code>used<\/code>\u53ea\u80fd\u901a\u8fc7\u7ed3\u675f\u8fdb\u7a0b\u6765\u5b9e\u73b0\uff1f<\/li>\n<\/ul>\n<p>\u8fd9\u4e48\u968f\u4fbf\u5c31\u91ca\u653e\u4e86buff\/cache\u6240\u5360\u7528\u7684\u5185\u5b58\uff0c\u8bf4\u660e\u5b83\u5c31\u4e0d\u91cd\u8981\uff0c\u6e05\u9664\u5b83\u4e0d\u4f1a\u5bf9\u7cfb\u7edf\u7684\u8fd0\u884c\u9020\u6210\u5f71\u54cd<\/p>\n<p>\u60f3\u8d77\u6765\u300aCSAPP\u300b\uff08\u6df1\u5165\u7406\u89e3\u8ba1\u7b97\u673a\u7cfb\u7edf\uff09\u91cc\u9762\u8bf4\u8fc7\u4e00\u53e5\u8bdd<\/p>\n<blockquote>\n<p>\u5b58\u50a8\u5668\u5c42\u6b21\u7ed3\u6784\u7684\u672c\u8d28\u662f\uff0c\u6bcf\u4e00\u5c42\u5b58\u50a8\u8bbe\u5907\u90fd\u662f\u8f83\u4f4e\u4e00\u5c42\u8bbe\u5907\u7684\u7f13\u5b58<\/p>\n<\/blockquote>\n<p><img decoding=\"async\" src=\"http:\/\/www.yezhou.me\/AppBlog\/images\/\u6570\u636e\u5e93\/\u5b58\u50a8\u5668\u5c42\u6b21\u7ed3\u6784.png\" alt=\"\u5b58\u50a8\u5668\u5c42\u6b21\u7ed3\u6784\" \/><\/p>\n<p>\u7ffb\u8bd1\u6210\u4eba\u8bdd\uff0c\u5c31\u662f\u8bf4<strong>Linux\u4f1a\u628a\u5185\u5b58\u5f53\u4f5c\u662f\u786c\u76d8\u7684\u9ad8\u901f\u7f13\u5b58<\/strong><\/p>\n<blockquote>\n<p>\u76f8\u5173\u8d44\u6599\uff1a<a target=\"_blank\" rel=\"noopener\" href=\"http:\/\/tldp.org\/LDP\/sag\/html\/buffer-cache.html\">http:\/\/tldp.org\/LDP\/sag\/html\/buffer-cache.html<\/a><\/p>\n<\/blockquote>\n<h2>Join\u7b97\u6cd5<\/h2>\n<p>\u9762\u8bd5\u5b98\uff1a\u5982\u679c\u8ba9\u4f60\u6765\u5b9e\u73b0Join\u7b97\u6cd5\u4f60\u4f1a\u600e\u4e48\u505a\uff1f<\/p>\n<p>\u6211\uff1a\u65e0\u7d22\u5f15\u7684\u8bdd\uff0c\u5d4c\u5957\u5faa\u73af\u5c31\u5b8c\u4e8b\u4e86\u55f7\u3002\u6709\u7d22\u5f15\u7684\u8bdd\uff0c\u5219\u53ef\u4ee5\u5229\u7528\u7d22\u5f15\u6765\u63d0\u5347\u6027\u80fd.<\/p>\n<p>\u9762\u8bd5\u5b98\uff1a\u8bf4\u56dejoin_buffer\u00a0\u4f60\u8ba4\u4e3ajoin_buffer\u91cc\u9762\u5b58\u50a8\u7684\u662f\u4ec0\u4e48\uff1f<\/p>\n<p>\u6211\uff1a\u5728\u626b\u63cf\u8fc7\u7a0b\u4e2d\uff0c\u6570\u636e\u5e93\u4f1a\u9009\u62e9\u4e00\u4e2a\u8868\u628a\u4ed6\u8981\u8fd4\u56de\u4ee5\u53ca\u9700\u8981\u8fdb\u884c\u548c\u5176\u4ed6\u8868\u8fdb\u884c\u6bd4\u8f83\u7684\u6570\u636e\u653e\u8fdbjoin_buffer<\/p>\n<p>\u9762\u8bd5\u5b98\uff1a\u6709\u7d22\u5f15\u7684\u60c5\u51b5\u4e0b\u662f\u600e\u4e48\u5904\u7406\u7684\uff1f<\/p>\n<p>\u6211\uff1a\u8fd9\u4e2a\u5c31\u6bd4\u8f83\u7b80\u5355\u4e86\uff0c\u76f4\u63a5\u8bfb\u53d6\u4e24\u4e2a\u8868\u7684\u7d22\u5f15\u6811\u8fdb\u884c\u6bd4\u8f83\u5c31\u5b8c\u4e8b\u4e86\u55f7\uff0c\u6211\u8fd9\u8fb9\u4ecb\u7ecd\u4e00\u4e0b\u65e0\u7d22\u5f15\u7684\u5904\u7406\u65b9\u5f0f<\/p>\n<p>\uff081\uff09Nested Loop Join<\/p>\n<pre><code class=\"language-java\">sql = &#039;select * from outerTable left join innerTable on&#039;\n      + &#039;outerTable.id = innerTable.id&#039;\nfor (outerRow in outerTable) {\n  for (innerRow in innerTable) {\n    if (compare(outerRow, innerRow)) {\n      resultRow combine(outerRow, innerRow)\n      sendToReplyBuffer(resultRow)\n    }\n  }\n}<\/code><\/pre>\n<p>\u5d4c\u5957\u5faa\u73af\uff0c\u6bcf\u6b21\u53ea\u8bfb\u53d6\u8868\u4e2d\u7684\u4e00\u884c\u6570\u636e\uff0c\u4e5f\u5c31\u662f\u8bf4\u5982\u679couterTable\u670910\u4e07\u884c\u6570\u636e\uff0cinnerTable\u6709100\u884c\u6570\u636e\uff0c\u9700\u8981\u8bfb\u53d610000000\u6b21\uff08\u5047\u8bbe\u8fd9\u4e24\u4e2a\u8868\u7684\u6587\u4ef6\u6ca1\u6709\u88ab\u64cd\u4f5c\u7cfb\u7edf\u7ed9\u7f13\u5b58\u5230\u5185\u5b58\uff0c\u6211\u4eec\u79f0\u4e4b\u4e3a\u51b7\u6570\u636e\u8868\uff09<\/p>\n<p>\u5f53\u7136\u73b0\u5728\u6ca1\u5565\u6570\u636e\u5e93\u5f15\u64ce\u4f7f\u7528\u8fd9\u79cd\u7b97\u6cd5\uff08\u592a\u6162\u4e86\uff09<\/p>\n<p>\uff082\uff09Block Nested Loop<\/p>\n<pre><code class=\"language-java\">byte[] joinBuffer = new byte[joinBufferSize]\n\nfor (; fi11(joinBuffer, outerTable) != EOF;) {\n  for (innerRow in innerTable) {\n    for (outerRow in joinBuffer) {\n      if (compare(outerRow, innerRow) {\n        resultRow = combine(outerRow, innerRow)\n        sendToReplyBuffer(resultRow)\n      }\n    }\n  }\n}<\/code><\/pre>\n<p>Block \u5757\uff0c\u4e5f\u5c31\u662f\u8bf4\u6bcf\u6b21\u90fd\u4f1a\u53d6\u4e00\u5757\u6570\u636e\u5230\u5185\u5b58\u4ee5\u51cf\u5c11I\/O\u7684\u5f00\u9500<\/p>\n<p>\u5f53\u6ca1\u6709\u7d22\u5f15\u53ef\u4ee5\u4f7f\u7528\u7684\u65f6\u5019\uff0cMySQL InnoDB \u5c31\u4f1a\u4f7f\u7528\u8fd9\u79cd\u7b97\u6cd5<\/p>\n<p>\u8003\u8651\u4ee5\u4e0b\u4e24\u4e2a\u8868 t_a \u548ct_b<\/p>\n<pre><code class=\"language-sql\">CREATE TABLE `t_a` (\n  `id` int(11) NOT NULL,\n  `content` varchar(32) DEFAULT NULL,\n  `str_idx` varchar(32) DEFAULT NULL\n) ENGINE=InnoDB DEFAULT CHARSET=latin1;\n\nALTER TABLE `t_a` ADD PRIMARY KEY (`id`), ADD KEY `str_idx` (`str_idx`);\nALTER TABLE `t_a` MODIFY `id` int(11) NOT NULL AUTO_INCREMENT;<\/code><\/pre>\n<pre><code class=\"language-sql\">CREATE TABLE `t_b` (\n  `id` int(11) NOT NULL,\n  `content` varchar(32) DEFAULT NULL,\n  `str_idx` varchar(32) DEFAULT NULL\n) ENGINE=InnoDB DEFAULT CHARSET=latin1;\n\nALTER TABLE `t_b` ADD PRIMARY KEY (`id`), ADD KEY `str_idx` (`str_idx`);\nALTER TABLE `t_b` MODIFY `id` int(11) NOT NULL AUTO_INCREMENT;<\/code><\/pre>\n<pre><code class=\"language-sql\">mysql&gt; desc t_a;\n+---------+-------------+------+-----+---------+----------------+\n| Field   | Type        | Null | Key | Default | Extra          |\n+---------+-------------+------+-----+---------+----------------+\n| id      | int(11)     | NO   | PRI | NULL    | auto_increment |\n| content | varchar(32) | YES  |     | NULL    |                |\n| str_idx | varchar(32) | YES  | MUL | NULL    |                |\n+---------+-------------+------+-----+---------+----------------+\n3 rows in set (0.00 sec)\n\nmysql&gt; desc t_b;\n+---------+-------------+------+-----+---------+----------------+\n| Field   | Type        | Null | Key | Default | Extra          |\n+---------+-------------+------+-----+---------+----------------+\n| id      | int(11)     | NO   | PRI | NULL    | auto_increment |\n| content | varchar(32) | YES  |     | NULL    |                |\n| str_idx | varchar(32) | YES  | MUL | NULL    |                |\n+---------+-------------+------+-----+---------+----------------+\n3 rows in set (0.00 sec)<\/code><\/pre>\n<p>\u5f53\u65e0\u6cd5\u4f7f\u7528\u7d22\u5f15\u6267\u884cjoin\u64cd\u4f5c\u7684\u65f6\u5019\uff0cInnoDB\u4f1a\u81ea\u52a8\u4f7f\u7528 Block Nested Loop \u7b97\u6cd5<\/p>\n<pre><code class=\"language-sql\">mysql&gt; explain select * from t_b left join t_a on t_b.content = t_b.content;\n+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+\n| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                                              |\n+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+\n|  1 | SIMPLE      | t_b   | ALL  | NULL          | NULL | NULL    | NULL |    1 | NULL                                               |\n|  1 | SIMPLE      | t_a   | ALL  | NULL          | NULL | NULL    | NULL |    1 | Using where; Using join buffer (Block Nested Loop) |\n+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+\n2 rows in set (0.00 sec)<\/code><\/pre>\n<h2>\u603b\u7ed3<\/h2>\n<p>\u4e0a\u5b66\u65f6\uff0c\u6570\u636e\u5e93\u8001\u5e08\u6700\u559c\u6b22\u8003\u6570\u636e\u5e93\u8303\u5f0f\uff0c\u76f4\u5230\u4e0a\u73ed\u624d\u5b66\u4f1a\u4e00\u5207\u4ee5\u6027\u80fd\u4e3a\u51c6\uff0c\u80fd\u5197\u4f59\u5c31\u5197\u4f59\uff0c\u5b9e\u5728\u5197\u4f59\u4e0d\u4e86\u7684\u5c31join\u3002\u5982\u679cjoin\u771f\u7684\u5f71\u54cd\u5230\u6027\u80fd\uff0c\u8bd5\u7740\u8c03\u5927<code>join_buffer_size<\/code>\uff0c\u6216\u8005\u6362\u56fa\u6001\u786c\u76d8\u3002<\/p>\n<p>\u53c2\u8003\u8d44\u6599\uff1a<\/p>\n<ul>\n<li>\u300a\u6df1\u5165\u7406\u89e3\u8ba1\u7b97\u673a\u7cfb\u7edf\u300b- \u7b2c6\u7ae0 \u5b58\u50a8\u5668\u5c42\u6b21\u7ed3\u6784<\/li>\n<li><a target=\"_blank\" rel=\"noopener\" href=\"https:\/\/www.linuxatemyram.com\/play.html\">https:\/\/www.linuxatemyram.com\/play.html<\/a> \u4f5c\u8005\u901a\u8fc7\u51e0\u4e2a\u4f8b\u5b50\u6765\u8bf4\u660e\u786c\u76d8\u7f13\u5b58\u5bf9\u7a0b\u5e8f\u6267\u884c\u6027\u80fd\u7684\u5f71\u54cd<\/li>\n<li><a target=\"_blank\" rel=\"noopener\" href=\"https:\/\/www.linuxatemyram.com\/\">https:\/\/www.linuxatemyram.com\/<\/a> Free\u53c2\u6570\u7684\u89e3\u91ca<\/li>\n<li><a target=\"_blank\" rel=\"noopener\" href=\"https:\/\/www.thegeekdiary.com\/how-to-clear-the-buffer-pagecache-disk-cache-under-linux\/\">https:\/\/www.thegeekdiary.com\/how-to-clear-the-buffer-pagecache-disk-cache-under-linux\/<\/a> \u6587\u7ae0\u5f00\u5934\u9001\u5206\u9898\u547d\u4ee4\u7684\u89e3\u91ca<\/li>\n<li><a target=\"_blank\" rel=\"noopener\" href=\"https:\/\/juejin.im\/book\/5bffcbc9f265da614b11b731\/section\/5c061a4de51d451df113c10d\">https:\/\/juejin.im\/book\/5bffcbc9f265da614b11b731\/section\/5c061a4de51d451df113c10d<\/a> MySQL \u662f\u600e\u6837\u8fd0\u884c\u7684\uff1a\u4ece\u6839\u513f\u4e0a\u7406\u89e3 MySQL<\/li>\n<li><a target=\"_blank\" rel=\"noopener\" href=\"https:\/\/mariadb.com\/kb\/en\/block-based-join-algorithms\/\">https:\/\/mariadb.com\/kb\/en\/block-based-join-algorithms\/<\/a> \u6765\u81eaMariaDB\u5b98\u65b9\u6587\u6863\u89e3\u91ca\u4e86Block-Nested-Loop\u7b97\u6cd5\u7684\u5b9e\u73b0<\/li>\n<\/ul>\n<blockquote>\n<p>\u8f6c\u8f7d\u81f3\uff1a<a target=\"_blank\" rel=\"noopener\" href=\"https:\/\/blog.csdn.net\/u013939918\/article\/details\/106736557\">https:\/\/blog.csdn.net\/u013939918\/article\/details\/106736557<\/a><\/p>\n<\/blockquote>\n","protected":false},"excerpt":{"rendered":"<p>free\u547d\u4ee4\u7f13\u5b58buff\/cache \u67e5\u770b\u5185\u5b58\u7684\u547d\u4ee4\uff1afree \u6216\u8005 top\uff0c\u5176\u4e2d\u4f7f\u7528free\u547d\u4ee4\u90fd\u53ef\u4ee5\u770b\u5230\u4fe1 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