一、介绍
1、分析SQL执行带来的开销是优化SQL的重要手段。
2、在MySQL数据库中，可以通过配置profiling参数来启用SQL剖析。
3、该参数可以在全局和session级别来设置。
4、对于全局级别则作用于整个MySQL实例，而session级别紧影响当前session。
5、该参数开启后，后续执行的SQL语句都将记录其资源开销，诸如IO，上下文切换，CPU，Memory等等。根据这些开销进一步分析当前SQL瓶颈从而进行优化与调整。
二、有关profile的描述show variables like 'version';
show variables like '%profil%';
mysql> show variables like '%profil%';
+------------------------+-------+
| 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
+------------------------+-------+
3 rows in set (0.00 sec)--获取profile的帮助
root@localhost[sakila]> help profile;
Name: 'SHOW PROFILE'
Description:
Syntax:
SHOW PROFILE [type [, type] ... ]
[FOR QUERY n]
[LIMIT row_count [OFFSET offset]]
type:
ALL --显示所有的开销信息
| BLOCK IO --显示块IO相关开销
| CONTEXT SWITCHES --上下文切换相关开销
| CPU --显示CPU相关开销信息
| IPC --显示发送和接收相关开销信息
| MEMORY --显示内存相关开销信息
| PAGE FAULTS --显示页面错误相关开销信息
| SOURCE --显示和Source_function，Source_file，Source_line相关的开销信息
| SWAPS --显示交换次数相关开销的信息
2、开启porfiling --启用session级别的profiling
root@localhost[sakila]> set profiling=1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
--验证修改后的结果
root@localhost[sakila]> show variables like '%profil%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| have_profiling | YES |
| profiling | ON |
| profiling_history_size | 15 |
+------------------------+-------+
--发布SQL查询
root@localhost[sakila]> select count(*) from customer;
+----------+
| count(*) |
+----------+
| 599 |
+----------+
--查看当前session所有已产生的profile
root@localhost[sakila]> show profiles;
+----------+------------+--------------------------------+
| Query_ID | Duration | Query |
+----------+------------+--------------------------------+
| 1 | 0.00253600 | show variables like '%profil%' |
| 2 | 0.00138150 | select count(*) from customer |
+----------+------------+--------------------------------+
2 rows in set, 1 warning (0.01 sec)
--我们看到有2个warning，之前一个，现在一个
root@localhost[sakila]> show warnings; --下面的结果表明SHOW PROFILES将来会被Performance Schema替换掉
+---------+------+--------------------------------------------------------------------------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------------------------------------------------------------------------+
| Warning | 1287 | 'SHOW PROFILES' is deprecated and will be removed in a future release. Please use Performance Schema instead |
+---------+------+--------------------------------------------------------------------------------------------------------------+ 3、获取SQL语句的开销信息
--可以直接使用show profile来查看上一条SQL语句的开销信息
--注，show profile之类的语句不会被profiling，即自身不会产生Profiling
--我们下面的这个show profile查看的是show warnings产生的相应开销
root@localhost[sakila]> show profile;
+----------------+----------+
| Status | Duration |
+----------------+----------+
| starting | 0.000141 |
| query end | 0.000058 |
| closing tables | 0.000014 |
| freeing items | 0.001802 |
| cleaning up | 0.000272 |
+----------------+----------+
--如下面的查询show warnings被添加到profiles
root@localhost[sakila]> show profiles;
+----------+------------+--------------------------------+
| Query_ID | Duration | Query |
+----------+------------+--------------------------------+
| 1 | 0.00253600 | show variables like '%profil%' |
| 2 | 0.00138150 | select count(*) from customer |
| 3 | 0.00228600 | show warnings |
+----------+------------+--------------------------------+
--获取指定查询的开销
root@localhost[sakila]> show profile for query 2;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000148 |
| checking permissions | 0.000014 |
| Opening tables | 0.000047 |
| init | 0.000023 |
| System lock | 0.000035 |
| optimizing | 0.000012 |
| statistics | 0.000019 |
| preparing | 0.000014 |
| executing | 0.000006 |
| Sending data | 0.000990 |
| end | 0.000010 |
| query end | 0.000011 |
| closing tables | 0.000010 |
| freeing items | 0.000016 |
| cleaning up | 0.000029 |
+----------------------+----------+
--查看特定部分的开销，如下为CPU部分的开销
root@localhost[sakila]> show profile cpu for query 2 ;
+----------------------+----------+----------+------------+
| Status | Duration | CPU_user | CPU_system |
+----------------------+----------+----------+------------+
| starting | 0.000148 | 0.000000 | 0.000000 |
| checking permissions | 0.000014 | 0.000000 | 0.000000 |
| Opening tables | 0.000047 | 0.000000 | 0.000000 |
| init | 0.000023 | 0.000000 | 0.000000 |
| System lock | 0.000035 | 0.000000 | 0.000000 |
| optimizing | 0.000012 | 0.000000 | 0.000000 |
| statistics | 0.000019 | 0.000000 | 0.000000 |
| preparing | 0.000014 | 0.000000 | 0.000000 |
| executing | 0.000006 | 0.000000 | 0.000000 |
| Sending data | 0.000990 | 0.001000 | 0.000000 |
| end | 0.000010 | 0.000000 | 0.000000 |
| query end | 0.000011 | 0.000000 | 0.000000 |
| closing tables | 0.000010 | 0.000000 | 0.000000 |
| freeing items | 0.000016 | 0.000000 | 0.000000 |
| cleaning up | 0.000029 | 0.000000 | 0.000000 |
+----------------------+----------+----------+------------+
--如下为MEMORY部分的开销
root@localhost[sakila]> show profile memory for query 2 ;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000148 |
| checking permissions | 0.000014 |
| Opening tables | 0.000047 |
| init | 0.000023 |
| System lock | 0.000035 |
| optimizing | 0.000012 |
| statistics | 0.000019 |
| preparing | 0.000014 |
| executing | 0.000006 |
| Sending data | 0.000990 |
| end | 0.000010 |
| query end | 0.000011 |
| closing tables | 0.000010 |
| freeing items | 0.000016 |
| cleaning up | 0.000029 |
+----------------------+----------+
--同时查看不同资源开销
root@localhost[sakila]> show profile block io,cpu for query 2;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000148 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000014 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000047 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000023 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000035 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000012 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.000019 | 0.000000 | 0.000000 | 0 | 0 |
| preparing | 0.000014 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.000990 | 0.001000 | 0.000000 | 0 | 0 |
| end | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000016 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000029 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
--下面的SQL语句用于查询query_id为2的SQL开销，且按最大耗用时间倒序排列
root@localhost[sakila]> set @query_id=2;
root@localhost[sakila]> SELECT STATE, SUM(DURATION) AS Total_R,
-> ROUND(
-> 100 * SUM(DURATION) /
-> (SELECT SUM(DURATION)
-> FROM INFORMATION_SCHEMA.PROFILING
-> WHERE QUERY_ID = @query_id
-> ), 2) AS Pct_R,
-> COUNT(*) AS Calls,
-> SUM(DURATION) / COUNT(*) AS "R/Call"
-> FROM INFORMATION_SCHEMA.PROFILING
-> WHERE QUERY_ID = @query_id
-> GROUP BY STATE
-> ORDER BY Total_R DESC;
+----------------------+----------+-------+-------+--------------+
| STATE | Total_R | Pct_R | Calls | R/Call |
+----------------------+----------+-------+-------+--------------+
| Sending data | 0.000990 | 71.53 | 1 | 0.0009900000 |--最大耗用时间部分为发送数据
| starting | 0.000148 | 10.69 | 1 | 0.0001480000 |
| Opening tables | 0.000047 | 3.40 | 1 | 0.0000470000 |
| System lock | 0.000035 | 2.53 | 1 | 0.0000350000 |
| cleaning up | 0.000029 | 2.10 | 1 | 0.0000290000 |
| init | 0.000023 | 1.66 | 1 | 0.0000230000 |
| statistics | 0.000019 | 1.37 | 1 | 0.0000190000 |
| freeing items | 0.000016 | 1.16 | 1 | 0.0000160000 |
| preparing | 0.000014 | 1.01 | 1 | 0.0000140000 |
| checking permissions | 0.000014 | 1.01 | 1 | 0.0000140000 |
| optimizing | 0.000012 | 0.87 | 1 | 0.0000120000 |
| query end | 0.000011 | 0.79 | 1 | 0.0000110000 |
| end | 0.000010 | 0.72 | 1 | 0.0000100000 |
| closing tables | 0.000010 | 0.72 | 1 | 0.0000100000 |
| executing | 0.000006 | 0.43 | 1 | 0.0000060000 |
+----------------------+----------+-------+-------+--------------+
--开启profiling后，我们可以通过show profile等方式查看，其实质是这些开销信息被记录到information_schema.profiling表
--如下面的查询，部分信息省略
profiling
root@localhost[information_schema]> select * from profiling limit 3,3\G;
*************************** 1. row ***************************
QUERY_ID: 1
SEQ: 5
STATE: init
DURATION: 0.000020
CPU_USER: 0.000000
CPU_SYSTEM: 0.000000
CONTEXT_VOLUNTARY: 0
CONTEXT_INVOLUNTARY: 0
BLOCK_OPS_IN: 0
BLOCK_OPS_OUT: 0
MESSAGES_SENT: 0
MESSAGES_RECEIVED: 0
PAGE_FAULTS_MAJOR: 0
PAGE_FAULTS_MINOR: 0
SWAPS: 0
SOURCE_FUNCTION: mysql_prepare_select
SOURCE_FILE: sql_select.cc
SOURCE_LINE: 1050
--停止profile,可以设置profiling参数，或者在session退出之后,profiling会被自动关闭
root@localhost[sakila]> set profiling=off;
Query OK, 0 rows affected, 1 warning (0.00 sec) 本文摘抄自MySQL性能分析工具profile使用教程