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。
1、有关profile的描述
--当前版本 root@localhost[sakila]> show variables like 'version'; +---------------+---------------------------------------+ | Variable_name | Value | +---------------+---------------------------------------+ | version | 5.6.17-enterprise-commercial-advanced | +---------------+---------------------------------------+ --查看profiling系统变量 root@localhost[sakila]> 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时将禁用profiling +------------------------+-------+ --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 --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
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 3,3G; *************************** 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)
这里还需要注意一点就是，需要安装profile模块才能实现。
1、不过版本要在5.0.37之后。(SHOW PROFILES and SHOW PROFILE were added in MySQL 5.0.37.)
SELECT @@profiling;
来查看是否已经启用profile，如果profilng值为0，可以通过
SET profiling = 1;
来启用。启用profiling之后，我们执行一条查询语句，比如：
select count(*) from roi_summary;
然后show profiles查看如下：
+----------------+------------+----------------------------------+ | Query_ID | Duration | Query | +----------------+------------+----------------------------------+ | 1 | 0.00021500 | select @@profiling | | 2 | 0.05522700 | select count(*) from roi_summary | +----------------+------------+----------------------------------+
2 rows in set (0.00 sec)
其中ID为5的语句是刚执行的查询语句
2、变量profiling是用户变量，每次都得重新启用。
以下是我做的一些实验。数据很明显，就不多解释了。
mysql> use test Database changed mysql> set profiling=1; Query OK, 0 rows affected (0.00 sec) mysql> show tables; +----------------+ | Tables_in_test | +----------------+ | bag_item | | bag_user | | score | | t | +----------------+ 4 rows in set (0.03 sec) mysql> select count(*) from t; +----------+ | count(*) | +----------+ | 2097152 | +----------+ 1 row in set (0.74 sec) mysql> show profiles; +----------+------------+------------------------+ | Query_ID | Duration | Query | +----------+------------+------------------------+ | 1 | 0.02717000 | show tables | | 2 | 0.74770100 | select count(*) from t | +----------+------------+------------------------+ 2 rows in set (0.00 sec) mysql> show profile for query 2; +--------------------------------+----------+ | Status | Duration | +--------------------------------+----------+ | (initialization) | 0.000004 | | checking query cache for query | 0.000044 | | Opening tables | 0.000012 | | System lock | 0.000017 | | Table lock | 0.00003 | | init | 0.000013 | | optimizing | 0.000008 | | statistics | 0.000013 | | preparing | 0.000011 | | executing | 0.000006 | | Sending data | 0.747313 | | end | 0.000014 | | query end | 0.000006 | | storing result in query cache | 0.000006 | | freeing items | 0.000012 | | closing tables | 0.000009 | | logging slow query | 0.000183 | +--------------------------------+----------+ 17 rows in set (0.00 sec) mysql> show profile block io,cpu for query 2; +--------------------------------+----------+----------+------------+--------------+---------------+ | Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out | +--------------------------------+----------+----------+------------+--------------+---------------+ | (initialization) | 0.000004 | 0 | 0 | 0 | 0 | | checking query cache for query | 0.000044 | 0 | 0 | 0 | 0 | | Opening tables | 0.000012 | 0 | 0 | 0 | 0 | | System lock | 0.000017 | 0 | 0 | 0 | 0 | | Table lock | 0.00003 | 0 | 0 | 0 | 0 | | init | 0.000013 | 0 | 0 | 0 | 0 | | optimizing | 0.000008 | 0 | 0 | 0 | 0 | | statistics | 0.000013 | 0 | 0 | 0 | 0 | | preparing | 0.000011 | 0 | 0 | 0 | 0 | | executing | 0.000006 | 0 | 0 | 0 | 0 | | Sending data | 0.747313 | 0.746887 | 0 | 0 | 0 | | end | 0.000014 | 0 | 0 | 0 | 0 | | query end | 0.000006 | 0 | 0 | 0 | 0 | | storing result in query cache | 0.000006 | 0 | 0 | 0 | 0 | | freeing items | 0.000012 | 0 | 0 | 0 | 0 | | closing tables | 0.000009 | 0 | 0 | 0 | 0 | | logging slow query | 0.000183 | 0 | 0 | 0 | 0 | +--------------------------------+----------+----------+------------+--------------+---------------+ 17 rows in set (0.00 sec) mysql> insert into t(username) select username from t; Query OK, 2097152 rows affected (34.17 sec) Records: 2097152 Duplicates: 0 Warnings: 0 mysql> show profiles; +----------+-------------+------------------------------------------------+ | Query_ID | Duration | Query | +----------+-------------+------------------------------------------------+ | 1 | 0.02717000 | show tables | | 2 | 0.74770100 | select count(*) from t | | 3 | 0.00004200 | show prifile for query 2 | | 4 | 34.30410100 | insert into t(username) select username from t | +----------+-------------+------------------------------------------------+ 4 rows in set (0.00 sec) mysql> show profile cpu,block io,memory,swaps for query 4; mysql> select count(*) from t; +----------+ | count(*) | +----------+ | 4194304 | +----------+ 1 row in set (1.51 sec) mysql> show profiles; +----------+-------------+------------------------------------------------+ | Query_ID | Duration | Query | +----------+-------------+------------------------------------------------+ | 1 | 0.02717000 | show tables | | 2 | 0.74770100 | select count(*) from t | | 3 | 0.00004200 | show prifile for query 2 | | 4 | 34.30410100 | insert into t(username) select username from t | | 5 | 1.50563800 | select count(*) from t | +----------+-------------+------------------------------------------------+ 5 rows in set (0.00 sec) mysql> show profile cpu,block io,memory,swaps,context switches,source for query 5; …… mysql> update t set username = 'waill'; Query OK, 4194304 rows affected (44.82 sec) Rows matched: 4194304 Changed: 4194304 Warnings: 0 mysql> show profiles; +----------+-------------+------------------------------------------------+ | Query_ID | Duration | Query | +----------+-------------+------------------------------------------------+ | 1 | 0.02717000 | show tables | | 2 | 0.74770100 | select count(*) from t | | 3 | 0.00004200 | show prifile for query 2 | | 4 | 34.30410100 | insert into t(username) select username from t | | 5 | 1.50563800 | select count(*) from t | | 6 | 44.82054700 | update t set username = 'waill' | +----------+-------------+------------------------------------------------+ 6 rows in set (0.00 sec) mysql> show profile cpu,block io,memory,swaps,context switches,source for query 6;