[MySQL CPU]线上飙升800%，load达到12的解决过程_MySQL

接到报警通知，负载过高，达到800%，load也过高，有11了。

MySQL版本为5.6.12-log

1 top 之后，确实是mysqld进程占据了所有资源。

2 查看error日志，无任何异常

3 show eninge innodb status/G，没有死锁信息。

4 show full processlist;

没有耗时非常大的慢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。

到底是什么问题呢？查看slow log，发现如下SQL，频繁执行，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' 	->	 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判断引起的，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。

还记录以前碰到的

(Block Nested Loop)的案例是 join后面的on条件里面有or判断。

也会引起Block Nested Loop，导致数据库负载过高。