[MySQL CPU]线上飙升800%,load达到12的解决过程

接到报警通知,负载过高,达到800%,load也过高,有11了。

MySQL版本号为5.6.12-log


1 top 之后,确实是mysqld进程占领了全部资源。


2 查看error日志,无不论什么异常


3 show eninge innodb status\G,没有死锁信息。


4 show full processlist;

没有耗时很大的慢sql再跑。看并发,当前的线程总数量也才30个左右。


5 查看iostat,读写正常。


究竟是什么问题呢?查看slow log,发现例如以下SQL,频繁运行,耗时在5秒之间,explain有Using join buffer (Block Nested Loop)

mysql> explain select web_page_object.web_page_object_id,
    ->     web_page_object.object_id,
    ->     web_div_name,web_page_object.position_sort,web_page_object.end_time,om1.label,om1.file,jump_url,om2.label as label1,om2.file as file1
    ->     from web_page_div,web_page_object,object_media as om1,object_media as om2
    ->     where web_page_div.id=web_page_object.web_page_div_id
    ->     and web_page_object.object_media_id=om1.object_media_id
    ->     and web_page_div.web_page_id=1200
    ->     and if(web_page_object.object_media_id1=0,
    ->             web_page_object.object_media_id=om2.object_media_id,
    ->             web_page_object.object_media_id1=om2.object_media_id)
    ->    
    ->     and ‘2014-05-01 15:09:49‘>=start_time
    ->     and ‘2014-05-01 15:09:49‘<= end_time
    ->   
    ->     and object_status=0
    ->     order by web_page_div.id,web_page_object.position_sort;
+----+-------------+-----------------+--------+-----------------------+---------+---------+-------------------------------------------+-------+----------------------------------------------------+
| id | select_type | table           | type   | possible_keys         | key     | key_len | ref                                       | rows  | Extra                                              |
+----+-------------+-----------------+--------+-----------------------+---------+---------+-------------------------------------------+-------+----------------------------------------------------+
|  1 | SIMPLE      | web_page_object | ALL    | object_media_id_index | NULL    | NULL    | NULL                                      | 51165 | Using where; Using temporary; Using filesort       |
|  1 | SIMPLE      | web_page_div    | eq_ref | PRIMARY,idx           | PRIMARY | 4       | db_jiapin.web_page_object.web_page_div_id |     1 | Using where                                        |
|  1 | SIMPLE      | om1             | eq_ref | PRIMARY               | PRIMARY | 4       | db_jiapin.web_page_object.object_media_id |     1 | Using where                                        |
|  1 | SIMPLE      | om2             | ALL    | NULL                  | NULL    | NULL    | NULL                                      | 74759 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-----------------+--------+-----------------------+---------+---------+-------------------------------------------+-------+----------------------------------------------------+
Using join buffer (Block Nested Loop)


看SQL是where后面的if推断引起的,拆分if之后,就正常了,SQL耗时不到0.1秒。数据库load也降下来了。


还记录曾经碰到的

(Block Nested Loop)的案例是 join后面的on条件里面有or推断。
也会引起Block Nested Loop,导致数据库负载过高。



[MySQL CPU]线上飙升800%,load达到12的解决过程,古老的榕树,5-wow.com

郑重声明:本站内容如果来自互联网及其他传播媒体,其版权均属原媒体及文章作者所有。转载目的在于传递更多信息及用于网络分享,并不代表本站赞同其观点和对其真实性负责,也不构成任何其他建议。