分析诊断工具之三：使用show profiles分析SQL性能

　　分析SQL执行带来的开销是优化SQL的重要手段。在MySQL数据库中，可以通过配置profiling参数来启用SQL剖析。该参数可以在全局和session级别来设置。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。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。本文描述了如何使用MySQL profile，不涉及具体的样例分析。

如何查看执行SQL的耗时的步骤：开启profile、发送sql、查看profile的资源开销结果、关闭profile。

使用show profiles分析sql性能。

Show profiles是5.0.37之后添加的，要想使用此功能，要确保版本在5.0.37之后。

查看数据库版本

mysql> select version();

profile默认是不打开的

mysql> show profiles;
Empty set (0.02 sec)

验证修改后的结果

mysql> show variables like "%pro%";
可以看到profiling 默认是OFF的。

开启profile，然后测试

开启profile
mysql> set profiling=1;

获取profile的帮助  

help profile;  

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   
  
The SHOW PROFILE and SHOW PROFILES statements display profiling  
information that indicates resource usage for statements executed  
during the course of the current session.  
  
*Note*: These statements are deprecated as of MySQL 5.6.7 and will be  
removed in a future MySQL release. Use the Performance Schema instead;  
see http://dev.mysql.com/doc/refman/5.6/en/performance-schema.html.  
--上面描述从5.6.7开始该命令将会被移除，用Performance Schema instead代替  
--在Oracle数据库中，是通过autotrace来剖析单条SQL并获取真实的执行计划以及其开销信息  

执行业务SQL，并用profile分析示例：

--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 |  
+---------+------+--------------------------------------------------------------------------------------------------------------+ 

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（第二条查询的开销明细） 
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)