性能测试之数据库篇-查询（二）
profile 分析sql开销
1.使用之前先查看当前数据库的版本信息,低版本无法使用.
show version(); 或者 show variables like '%version%'
2.查看profiling
show variables like '%profil%' ;
result:
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| have_profiling | YES | --只读变量，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p
show profiles; 查看是否开启,效果同上.
3.查看使用说明
help profile;
4.开启profile
set profiling=1; 赋值时候不要有多余的空格.
5.运行sql,查看对应的profile
select * from test ;
show profiles;
result:
+----------+------------+--------------------------------------------------------------------------------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+--------------------------------------------------------------------------------------------------------------------------+
| 28 | 0.00033575 | select * from test |
+----------+------------+--------------------------------------------------------------------------------------------------------------------------+
分析sql性能,分析的时候可以加上对应的开销字段
show profile [cpu,io][all] for query 28 方括号中的开销项只为示意项，不见得就能执行 利用all 可全部代替
show profile for query 28 ;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 5.7E-5 |
| checking permissions | 7E-6 |
| Opening tables | 1.7E-5 |
| init | 2.3E-5 |
| System lock | 8E-6 |
| optimizing | 5E-6 |
| statistics | 1.1E-5 |
| preparing | 9E-6 |
| executing | 3E-6 |
| Sending data | 8.8E-5 |
| end | 5E-6 |
| query end | 6E-6 |
| closing tables | 5E-6 |
| freeing items | 7.8E-5 |
| cleaning up | 1.5E-5 |
+----------------------+----------+
6.关闭
set profiling=off;
文章参考https://www.php.cn/mysql-tutorials-416130.html
show profile ALL for query 10;
