1、慢查询SQL排查
1）、开启慢查询日志，可以让MySQL记录下查询超过指定时间的语句，通过定位分析性能的瓶颈，才能更好的优化数据库系统的性能。
2）、参数说明：
slow_query_log 慢查询开启状态
slow_query_log_file 慢查询日志存放的位置（这个目录需要MySQL运行帐号的可写权限，一般设置为MySQL的数据存放目录）
long_query_time 查询超过多少秒才记录
3）、查看慢查询相关参数
mysql> show variables like 'slow_query%';
+---------------------------+----------------------------------+
| Variable_name | Value |
+---------------------------+----------------------------------+
| slow_query_log | OFF |
| slow_query_log_file | /mysql/data/localhost-slow.log |
+---------------------------+----------------------------------+
mysql> show variables like 'long_query_time';
+-----------------+-----------+
| Variable_name | Value |
+-----------------+-----------+
| long_query_time | 10.000000 |
+-----------------+-----------+4）、设置方法
方法一：全局变量设置
将 slow_query_log 全局变量设置为“ON”状态
mysql> set global slow_query_log='ON';
设置慢查询日志存放的位置
mysql> set global slow_query_log_file='/data1/mysql/data/slow.log';
查询超过1秒就记录
mysql> set global long_query_time=1;
方法二：配置文件设置
修改配置文件my.cnf，在[mysqld]下的下方加入
[mysqld]
slow_query_log = ON
slow_query_log_file = /data1/mysql/data/slow.log
long_query_time = 1
重启MySQL服务
service mysqld restart
查看设置后的参数
mysql> show variables like 'slow_query%';
+---------------------+--------------------------------+
| Variable_name | Value |
+---------------------+--------------------------------+
| slow_query_log | ON |
| slow_query_log_file | /data1/mysql/data/slow.log |
+---------------------+--------------------------------+
mysql> show variables like 'long_query_time';
+-----------------+----------+
| Variable_name | Value |
+-----------------+----------+
| long_query_time | 1.000000 |
+-----------------+----------+
测试：
1.执行一条慢查询SQL语句
mysql> select sleep(2);
2.查看是否生成慢查询日志
ls /data1/mysql/data/slow.log
如果日志存在，MySQL开启慢查询设置成功！：
2、mysqldumpslow工具分析
mysqldumpslow --help可显示其参数的使用
经常使用的参数：
-s，是order的顺序
al 平均锁定时间
ar 平均返回记录时间
at 平均查询时间（默认）
c 计数
l 锁定时间
r 返回记录
t 查询时间
-t，是top n的意思，即为返回前面多少条的数据
-g，后边可以写一个正则匹配模式，大小写不敏感的
[root@PTZJ192 data]# mysqldumpslow -t 10 -s t -g "left join" slow.log
Reading mysql slow query log from slow.log
Died at /data1/mysql/bin/mysqldumpslow line 162, <> chunk 2.
[root@PTZJ192 data]# mysqldumpslow -t 10 -s t slow.log
Reading mysql slow query log from slow.log
Count: 2 Time=7.00s (14s) Lock=0.00s (0s) Rows=1.0 (2), root[root]@localhost
select sleep(N)
Died at /data1/mysql/bin/mysqldumpslow line 162, <> chunk 2.注意：使用mysqldumpslow的分析结果不会显示具体完整的sql语句
3、通过profiles分析
Show profiles是MySQL 5.0.37之后添加的，可以通过show version()查看MySQL的版本。
mysql> show variables like '%profil%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| have_profiling | YES | ---用于控制是否由系统变量开启或禁用profiling
| profiling | OFF | ---开启SQL语句剖析功能
| profiling_history_size | 15 | ---设置保留profiling的数目，缺省为15，范围为0至100，为0时将禁用profiling开启profiling
mysql> set profiling=1;
Query OK, 0 rows affected, 1 warning (0.00 sec)显示当前profiles：
mysql> show profiles;
+----------+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Query_ID | Duration | Query |
+----------+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 7 | 0.00022275 | SELECT * FROM setup_actors |
| 8 | 0.00016050 | SELECT DATABASE() |
| 9 | 0.00032350 | show databases |
| 10 | 0.00024050 | show tables |
| 11 | 0.00019250 | SELECT * FROM setup_actors |
| 12 | 0.00183950 | show variables like "profiling_hist%" |
| 13 | 0.00192500 | show variables like '%profil%' |
| 14 | 0.00011550 | show warnings |
| 15 | 0.00044725 | help 'show profile' |
| 16 | 0.00013875 | set profiling=1 |
| 17 | 0.00011550 | show warnings |
| 18 | 0.00025075 | select * from customers where `type` = 1 AND `status` < 7 AND `isarea` = 6 AND `into_time`>='2016-12-01'AND `into_time`<='2017-01-02 23:59:59' order by score desc limit 40,20 |
| 19 | 333.19133875 | select * from oms3.customers where `type` = 1 AND `status` < 7 AND `isarea` = 6 AND `into_time`>='2016-12-01'AND `into_time`<='2017-01-02 23:59:59' order by score desc limit 40,20 |
| 20 | 0.00011250 | show profilings |
| 21 | 0.00010975 | show profilings |获取指定查询的开销，对应上面profiles中的Query_ID:
mysql> SHOW PROFILE FOR QUERY 2;
+--------------------+----------+
| Status | Duration |
+--------------------+----------+
| starting | 0.000078 |
| Opening tables | 0.000031 |
| System lock | 0.000015 |
| Table lock | 0.000010 |
| init | 0.000012 |
| optimizing | 0.000019 |
| executing | 0.000022 |
| end | 0.000006 |
| query end | 0.000003 |
| freeing items | 0.000014 |
| logging slow query | 0.000003 |
| cleaning up | 0.000004 |
+--------------------+----------+
rows in set (0.00 sec)显示其他一些参数
mysql> SHOW PROFILE BLOCK IO, CPU FOR QUERY 2;
+--------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+--------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000078 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000031 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| Table lock | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000012 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000019 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000022 | 0.000000 | 0.000000 | 0 | 0 |
| end | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000003 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000014 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000003 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
+--------------------+----------+----------+------------+--------------+---------------+
rows in set (0.00 sec)4、全局查询日志
因为性能考虑，一般通用查询日志general log不会开启。查询日志会记录数据库所有的命令，不管正确与否。
如果开启查询日志，可以通过3种方式存储查询。
1）、将查询日志存放于指定的日志文件中；
2）、将查询日志存放于mysql.general_log表中；
3）、将查询日志同时存放于指定的日志文件与mysql库的general_log表中。
1,命令设置：(当前session有效)
//开启
set global general_log = 1
//定位table
set global log_output = 'TABLE';
2,配置文件设置：(全局有效)
mysql的配置文件my.cnf中
#开启
general_log = 1
#记录日志文件路径
general_log_file = /path/logfile
#输出格式
log_output = FILE
3,定位以及配置成功,当前session下操作的sql语句，将会记录在mysql库中general_log表:
mysql> select * from mysql.general_log;
+---------------------+---------------------------------+-----------+-----------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| event_time | user_host | thread_id | server_id | command_type | argument |
+---------------------+---------------------------------+-----------+-----------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 2018-01-16 21:27:49 | niushao[niushao] @ localhost [] | 358 | 1 | Query | SELECT bloginfo_id,bloginfo_title,bloginfo_describe,bloginfo_img,from_unixtime(bloginfo_createtime,'%Y') AS year,from_unixtime(bloginfo_createtime,'%m-%d') AS date,from_unixtime(bloginfo_createtime,'%Y-%m-%d') AS bloginfo_createtime,bloginfo_like,bloginfo_hate,bloginfo_click FROM ns_bloginfo WHERE bloginfo_status = 1 AND class_id=10 ORDER BY bloginfo_oid,bloginfo_id DESC |
| 2018-01-16 21:27:55 | niushao[niushao] @ localhost [] | 358 | 1 | Query | SELECT bloginfo_id,bloginfo_title,bloginfo_describe,bloginfo_img,from_unixtime(bloginfo_createtime,'%Y') AS year,from_unixtime(bloginfo_createtime,'%m-%d') AS date,from_unixtime(bloginfo_createtime,'%Y-%m-%d') AS bloginfo_createtime,bloginfo_like,bloginfo_hate,bloginfo_click FROM ns_bloginfo WHERE bloginfo_status = 1 and class_id in (10,11,12,13,14,15) ORDER BY bloginfo_oid,bloginfo_id DESC |
| 2018-01-16 21:27:58 | niushao[niushao] @ localhost [] | 358 | 1 | Query | SHOW TABLES |
| 2018-01-16 21:28:03 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from ns_link |
| 2018-01-16 21:28:05 | niushao[niushao] @ localhost [] | 358 | 1 | Query | SHOW TABLES |
| 2018-01-16 21:28:16 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from ns_homepage |
| 2018-01-16 21:28:23 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from ns_class |
| 2018-01-16 21:28:27 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from ns_class |
| 2018-01-16 21:28:34 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from ns_class |
| 2018-01-16 21:28:45 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from mysql.general_log |
| 2018-01-16 21:28:48 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from mysql.general_log |
| 2018-01-16 21:29:01 | niushao[niushao] @ localhost [] | 358 | 1 | Query | select * from mysql.general_log |
+---------------------+---------------------------------+-----------+-----------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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