mysql - 分析连接以诊断 "too many connections"错误

Question

我的网站当前收到以下错误消息:建立数据库连接时出错。如果我继续/phpma，我会收到以下消息:#1040 - Too much Connections。

如果我重新启动mysqld，问题就会暂时消失。

不幸的是，它现在已经回来了三次。

我的专用盒子的内存也从 8Gb 降至不到 1Gb。

Total Memory    8181984 kB
Free Memory 99344 kB
Total Swap Memory   1051064
kB Free Swap Memory 0 kB

如果我进入服务器上的 mysql 并执行 SHOW PROCESSLIST，我会收到以下信息:

| 17181 | my_db | localhost | my_db | Query   | 35117 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'boraras-brigittae' AND wp_po |
| 17182 | my_db | localhost | my_db | Query   | 35118 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17183 | my_db | localhost | my_db | Query   | 35117 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'boraras-brigittae' AND wp_po |
| 17184 | my_db | localhost | my_db | Query   | 35117 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'boraras-brigittae' AND wp_po |
| 17185 | my_db | localhost | my_db | Query   | 35041 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'akysis-vespa' AND wp_posts.p |
| 17186 | my_db | localhost | my_db | Query   | 35050 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('images','profiledotline-gif') A |
| 17187 | my_db | localhost | my_db | Query   | 35050 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('images','picarrow-gif') AND (po |
| 17188 | my_db | localhost | my_db | Query   | 35043 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17189 | my_db | localhost | my_db | Query   | 35041 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('m','marginal') AND (post_type = |
| 17190 | my_db | localhost | my_db | Query   | 34989 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17191 | my_db | localhost | my_db | Query   | 34989 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('w','wet-dry-filter') AND (post_ |
| 17192 | my_db | localhost | my_db | Query   | 34990 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17193 | my_db | localhost | my_db | Query   | 34954 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'corydoras-sterbai' AND wp_po |
| 17194 | my_db | localhost | my_db | Query   | 34954 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17195 | my_db | localhost | my_db | Query   | 34955 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17196 | my_db | localhost | my_db | Query   | 34954 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17197 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17198 | my_db | localhost | my_db | Query   | 34955 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17199 | my_db | localhost | my_db | Query   | 34898 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17200 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17201 | my_db | localhost | my_db | Query   | 34898 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums','lofiversion','index-ph |
| 17202 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 17204 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17205 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'sawbwa-resplendens' AND wp_p |
| 17206 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'badis-sp-buxar' AND wp_posts |
| 17207 | my_db | localhost | my_db | Query   | 34898 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'melanotaenia-boesemani' AND  |
| 17208 | my_db | localhost | my_db | Query   | 34898 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'betta-prima' AND wp_posts.po |
| 17209 | my_db | localhost | my_db | Query   | 34865 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 17210 | my_db | localhost | my_db | Query   | 34897 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17211 | my_db | localhost | my_db | Query   | 34898 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17213 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17214 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17215 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('knowledge-base') AND (post_type |
| 17216 | my_db | localhost | my_db | Query   | 34865 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17217 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17218 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'badis-sp-buxar' AND wp_posts |
| 17219 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums','lofiversion','index-ph |
| 17220 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'betta-prima' AND wp_posts.po |
| 17221 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17222 | my_db | localhost | my_db | Query   | 34865 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17223 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17224 | my_db | localhost | my_db | Query   | 34865 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'hemichromis-lifalili' AND wp |
| 17225 | my_db | localhost | my_db | Query   | 34864 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17226 | my_db | localhost | my_db | Query   | 34862 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'apistogramma-borellii' AND w |
| 17227 | my_db | localhost | my_db | Query   | 34863 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'melanotaenia-lacustris' AND  |
| 17228 | my_db | localhost | my_db | Query   | 34862 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'melanotaenia-lacustris' AND  |
| 17229 | my_db | localhost | my_db | Query   | 34861 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'mikrogeophagus-altispinosus' |
| 17230 | my_db | localhost | my_db | Query   | 34861 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.ID = 25503 AND wp_posts.post_type = 'atta |
| 17231 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'piaractus-brachypomus' AND w |
| 17232 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17233 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('knowledge-base') AND (post_type |
| 17234 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17235 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 17236 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17237 | my_db | localhost | my_db | Query   | 34803 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 17238 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('m','migrate') AND (post_type =  |
| 17239 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'hemichromis-lifalili' AND wp |
| 17240 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17241 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 17242 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17243 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17244 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums','lofiversion','index-ph |
| 17245 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17246 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT post_modified_gmt FROM wp_posts WHERE post_status = 'publish' AND post_type IN ('post', 'page |
| 17247 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 17248 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'geophagus-brokopondo' AND wp |
| 17249 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND wp_posts.post_name = 'hyphessobrycon-amandae' AND  |
| 17253 | my_db | localhost | my_db | Query   | 34788 | Waiting for table level lock | SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  WHERE 1=1  AND wp_posts.post_type = 'post' AN |
| 17255 | my_db | localhost | my_db | Query   | 34786 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('knowledge-base') AND (post_type |
| 17260 | my_db | localhost | my_db | Query   | 34786 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('s','silver-sand') AND (post_typ |
| 17262 | my_db | localhost | my_db | Query   | 34786 | Waiting for table level lock | SELECT ID, post_name, post_parent FROM wp_posts WHERE post_name IN ('forums') AND (post_type = 'page |
| 25505 | root      | localhost | NULL      | Query   |     2 | NULL                         | SHOW PROCESSLIST                                                                                     

我尝试使用 --log-slow-queries[slow-queries] 标志运行 mysql 但它似乎没有做任何事情 - 我可以'至少在我的盒子上找不到一个名为 slow-queries 的文件。

我猜这是某个地方的可疑查询，但我不知道从哪里开始寻找!

<小时/>

编辑:点击和设置

• MySQL 目前最多同时运行 500 个连接
• PHP 的内存限制相当高(大约 1Gb)，因为我正在尝试对脚本进行一些性能测试
• 仅此网站(盒子上还有其他网站；目前均受到此错误的影响)每周收到约 30,000 名唯一访问者和 250,000 次点击

Answer 1

根据我在高负载水平下的经验，wordpress(我假设它是基于表名的 wordpress)对于慢速查询来说相当糟糕。一旦表达到一定大小(post 表是这里的主要问题)，查询就会变得非常慢，您需要进行优化以跟上步伐。

在 MySQL 优化术语中，它与分配给缓冲区和 MySQL 查询缓存的内存量有关，对于 WordPress 来说，它与尽可能多地从数据库卸载有关。

从堆栈顶部到底部，您可以执行一些不同的操作:

1. Wordpress 优化。简而言之，删除未使用的插件，添加页面缓存(W3 Total Cache 是黄金标准)，尽可能多地从数据库中卸载。还要考虑减少为每个帖子存储的“修订”数量( see here )。对于一个已有 5 年历史的网站，您的修订可能比帖子多得多，这会减慢帖子查找速度(代码片段中的查询都是帖子查找)。

2. MySQL 优化。这是一个棘手的问题，因为你可以调整一大堆刻度盘，而找到正确的平衡是一门黑暗的艺术。那里有很多文章和教程，我没有任何具体的推荐，但简单的谷歌就会出现很多关于可以对 my.cnf 文件进行调整的信息。