mysql trace_Mysql Trace 工具

MySQL 优化

表

CREATE TABLE `employees` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(24) NOT NULL DEFAULT '' COMMENT '姓名',

`age` int(11) NOT NULL DEFAULT '0' COMMENT '年龄',

`position` varchar(20) NOT NULL DEFAULT '' COMMENT '职位',

`hire_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '入职时间',

PRIMARY KEY (`id`),

KEY `idx_name_age_position` (`name`,`age`,`position`) USING BTREE

) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 COMMENT='员工记录表';

Trace 工具

mysql最终是否选择走索引或者一张表涉及多个索引，mysql最终如何选择索引，我们可以用trace工具来一查究竟，开启trace工具会影响mysql性能，所以只能临时分析sql使用，用完之后立即关闭

1. 开启Trace

set session optimizer_trace="enabled=on",end_markers_in_json=on;‐‐开启trace

select * from employees where name >'a' order by position;

sELECT * FROM information_schema.OPTIMIZER_TRACE;

执行这两句sql

select * from employees where name >'a' order by position;

sELECT * FROM information_schema.OPTIMIZER_TRACE;

提出来trace值

Title

{

"steps": [

{

"join_preparation": {

"select#": 1,

"steps": [

{

"expanded_query": "/* select#1 */ select `employees`.`id` AS `id`,`employees`.`name` AS `name`,`employees`.`age` AS `age`,`employees`.`position` AS `position`,`employees`.`hire_time` AS `hire_time` from `employees` where (`employees`.`name` > 'a') order by `employees`.`position`"

}

] /* steps */

} /* join_preparation */

},

{

"join_optimization": {

"select#": 1,

"steps": [

{

"condition_processing": {

"condition": "WHERE",

"original_condition": "(`employees`.`name` > 'a')",

"steps": [

{

"transformation": "equality_propagation",

"resulting_condition": "(`employees`.`name` > 'a')"

},