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。
1.有关profile的解释
--当前版本
mysql> show variables like 'version';
+---------------+------------+
| Variable_name | Value |
+---------------+------------+
| version | 5.5.29-log |
+---------------+------------+
--查看profiling系统变量
mysql> show variables like '%profil%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| profiling | OFF | --开启SQL语句剖析功能。0或OFF表示关闭(默认模式)。1或ON表示开启
| 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。这个参数在MySQL 5.6.8过期，在后期版本中会被移除。
+------------------------+-------+
如果将profiling_history_size参数设置为0，同样具有关闭MySQL的profiling效果。
--获取profile的帮助
mysql> help profile;
Name: 'SHOW PROFILE'
Description:
Syntax:
SHOW PROFILE [type [, type] ... ]
[FOR QUERY n] --如果不指定，只是显示最近执行的语句；如果指定会显示语句n，n对应query_id的值
[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
Profiling由会话级别参数profiling控制。缺省是显示状态和持续时间。
上面描述从5.6.7开始该命令将会被移除，用Performance Schema instead代替
2、开启porfiling
--启用session级别的profiling
mysql> set profiling=1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
--验证修改后的结果
mysql> show variables like '%profil%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| profiling | ON |
| profiling_history_size | 15 |
+------------------------+-------+
--执行SQL查询
mysql> show databases;
mysql> show tables;
mysql> select count(*) from emp
--查看当前session所有已产生的profile
mysql> show profiles;
+----------+------------+-------------------------------------------------------+
| Query_ID | Duration | Query |
--------------------------------------------------------------------------------+
| 1 | 0.00037700 | show variables like '%profil%' |
| 2 | 0.00029500 | show databases |
| 3 | 0.00030800 | show tables |
| 4 | 0.00135700 | select count(*) from emp
+----------+------------+-------------------------------------------------------+
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
mysql> show profile;
+--------------------+----------+
| Status | Duration |
+--------------------+----------+
| starting | 0.000997 |
| Opening tables | 0.000015 |
| System lock | 0.000003 |
| Table lock | 0.000515 |
| optimizing | 0.000093 |
| statistics | 0.151343 |
| preparing | 0.000082 |
| executing | 0.000027 |
| Sending data | 0.081436 |
| init | 0.000024 |
| optimizing | 0.000006 |
| statistics | 0.000006 |
| preparing | 0.000007 |
| executing | 0.000005 |
| Sending data | 0.000046 |
| end | 0.000004 |
| query end | 0.000003 |
| freeing items | 0.000076 |
| removing tmp table | 0.000006 |
| closing tables | 0.000004 |
| logging slow query | 0.000002 |
| cleaning up | 0.000004 |
+--------------------+----------+
--显示所有性能信息
mysql> show profile all for query 9;
+--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+------------------+---------------+-------------+
| Status | Duration | CPU_user | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out | Messages_sent | Messages_received | Page_faults_major | Page_faults_minor | Swaps | Source_function | Source_file | Source_line |
+--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+------------------+---------------+-------------+
| starting | 0.000997 | 0.000000 | 0.000000 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | NULL | NULL | NULL |
| Opening tables | 0.000015 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_base.cc | 4622 |
| System lock | 0.000003 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | lock.cc | 260 |
| Table lock | 0.000515 | 0.001000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | lock.cc | 271 |
| optimizing | 0.000093 | 0.000000 | 0.000000 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 835 |
| statistics | 0.151343 | 0.124981 | 0.023996 | 1 | 155 | 0 | 0 | 0 | 0 | 0 | 39 | 0 | unknown function | sql_select.cc | 1026 |
| preparing | 0.000082 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1048 |
| executing | 0.000027 | 0.000000 | 0.000000 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1789 |
| Sending data | 0.081436 | 0.072989 | 0.006999 | 0 | 82 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2347 |
| init | 0.000024 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2537 |
| optimizing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 835 |
| statistics | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1026 |
| preparing | 0.000007 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1048 |
| executing | 0.000005 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1789 |
| Sending data | 0.000046 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2347 |
| end | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2583 |
| query end | 0.000003 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 5123 |
| freeing items | 0.000076 | 0.001000 | 0.000000 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 6147 |
| removing tmp table | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 10929 |
| closing tables | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 10954 |
| logging slow query | 0.000002 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 1735 |
| cleaning up | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 1703 |
+--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+------------------+---------------+-------------+
--获取指定查询的开销
mysql> show profile for query 9;
+--------------------+----------+
| Status | Duration |
+--------------------+----------+
| starting | 0.000997 |
| Opening tables | 0.000015 |
| System lock | 0.000003 |
| Table lock | 0.000515 |
| optimizing | 0.000093 |
| statistics | 0.151343 |
| preparing | 0.000082 |
| executing | 0.000027 |
| Sending data | 0.081436 |
| init | 0.000024 |
| optimizing | 0.000006 |
| statistics | 0.000006 |
| preparing | 0.000007 |
| executing | 0.000005 |
| Sending data | 0.000046 |
| end | 0.000004 |
| query end | 0.000003 |
| freeing items | 0.000076 |
| removing tmp table | 0.000006 |
| closing tables | 0.000004 |
| logging slow query | 0.000002 |
| cleaning up | 0.000004 |
+--------------------+----------+
mysql> show profile for query 9 limit 3;
+----------------+----------+
| Status | Duration |
+----------------+----------+
| starting | 0.000997 |
| Opening tables | 0.000015 |
| System lock | 0.000003 |
+----------------+----------+
mysql> show profile for query 9 limit 3 offset 5;
+------------+----------+
| Status | Duration |
+------------+----------+
| statistics | 0.151343 |
| preparing | 0.000082 |
| executing | 0.000027 |
+------------+----------+
--查看特定部分的开销，如下为CPU部分的开销
mysql> show profile cpu for query 9;
+--------------------+----------+----------+------------+
| Status | Duration | CPU_user | CPU_system |
+--------------------+----------+----------+------------+
| starting | 0.000997 | 0.000000 | 0.000000 |
| Opening tables | 0.000015 | 0.000000 | 0.000000 |
| System lock | 0.000003 | 0.000000 | 0.000000 |
| Table lock | 0.000515 | 0.001000 | 0.000000 |
| optimizing | 0.000093 | 0.000000 | 0.000000 |
| statistics | 0.151343 | 0.124981 | 0.023996 |
| preparing | 0.000082 | 0.000000 | 0.000000 |
| executing | 0.000027 | 0.000000 | 0.000000 |
| Sending data | 0.081436 | 0.072989 | 0.006999 |
| init | 0.000024 | 0.000000 | 0.000000 |
| optimizing | 0.000006 | 0.000000 | 0.000000 |
| statistics | 0.000006 | 0.000000 | 0.000000 |
| preparing | 0.000007 | 0.000000 | 0.000000 |
| executing | 0.000005 | 0.000000 | 0.000000 |
| Sending data | 0.000046 | 0.000000 | 0.000000 |
| end | 0.000004 | 0.000000 | 0.000000 |
| query end | 0.000003 | 0.000000 | 0.000000 |
| freeing items | 0.000076 | 0.001000 | 0.000000 |
| removing tmp table | 0.000006 | 0.000000 | 0.000000 |
| closing tables | 0.000004 | 0.000000 | 0.000000 |
| logging slow query | 0.000002 | 0.000000 | 0.000000 |
| cleaning up | 0.000004 | 0.000000 | 0.000000 |
+--------------------+----------+----------+------------+
--如下为MEMORY部分的开销
mysql> show profile memory for query 9 ;
+--------------------+----------+
| Status | Duration |
+--------------------+----------+
| starting | 0.000997 |
| Opening tables | 0.000015 |
| System lock | 0.000003 |
| Table lock | 0.000515 |
| optimizing | 0.000093 |
| statistics | 0.151343 |
| preparing | 0.000082 |
| executing | 0.000027 |
| Sending data | 0.081436 |
| init | 0.000024 |
| optimizing | 0.000006 |
| statistics | 0.000006 |
| preparing | 0.000007 |
| executing | 0.000005 |
| Sending data | 0.000046 |
| end | 0.000004 |
| query end | 0.000003 |
| freeing items | 0.000076 |
| removing tmp table | 0.000006 |
| closing tables | 0.000004 |
| logging slow query | 0.000002 |
| cleaning up | 0.000004 |
+--------------------+----------+
--同时查看不同资源开销
mysql> show profile block io,cpu for query 9;
+--------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+--------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000997 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000003 | 0.000000 | 0.000000 | 0 | 0 |
| Table lock | 0.000515 | 0.001000 | 0.000000 | 0 | 0 |
| optimizing | 0.000093 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.151343 | 0.124981 | 0.023996 | 0 | 0 |
| preparing | 0.000082 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000027 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.081436 | 0.072989 | 0.006999 | 0 | 0 |
| init | 0.000024 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| preparing | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.000046 | 0.000000 | 0.000000 | 0 | 0 |
| end | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000003 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000076 | 0.001000 | 0.000000 | 0 | 0 |
| removing tmp table | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000002 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
+--------------------+----------+----------+------------+--------------+---------------+
--显示swap的次数。
mysql> show profile swaps for query 9;
+--------------------+----------+-------+
| Status | Duration | Swaps |
+--------------------+----------+-------+
| starting | 0.000997 | 0 |
| Opening tables | 0.000015 | 0 |
| System lock | 0.000003 | 0 |
| Table lock | 0.000515 | 0 |
| optimizing | 0.000093 | 0 |
| statistics | 0.151343 | 0 |
| preparing | 0.000082 | 0 |
| executing | 0.000027 | 0 |
| Sending data | 0.081436 | 0 |
| init | 0.000024 | 0 |
| optimizing | 0.000006 | 0 |
| statistics | 0.000006 | 0 |
| preparing | 0.000007 | 0 |
| executing | 0.000005 | 0 |
| Sending data | 0.000046 | 0 |
| end | 0.000004 | 0 |
| query end | 0.000003 | 0 |
| freeing items | 0.000076 | 0 |
| removing tmp table | 0.000006 | 0 |
| closing tables | 0.000004 | 0 |
| logging slow query | 0.000002 | 0 |
| cleaning up | 0.000004 | 0 |
+--------------------+----------+-------+
--下面的SQL语句用于查询query_id为9的SQL开销，且按最大耗用时间倒序排列
mysql> set @query_id=9;
mysql> 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 |
+--------------------+----------+-------+-------+--------------+
| statistics | 0.151349 | 64.49 | 2 | 0.0756745000 |--最大耗用时间部分为statistics
| Sending data | 0.081482 | 34.72 | 2 | 0.0407410000 |
| starting | 0.000997 | 0.42 | 1 | 0.0009970000 |
| Table lock | 0.000515 | 0.22 | 1 | 0.0005150000 |
| optimizing | 0.000099 | 0.04 | 2 | 0.0000495000 |
| preparing | 0.000089 | 0.04 | 2 | 0.0000445000 |
| freeing items | 0.000076 | 0.03 | 1 | 0.0000760000 |
| executing | 0.000032 | 0.01 | 2 | 0.0000160000 |
| init | 0.000024 | 0.01 | 1 | 0.0000240000 |
| Opening tables | 0.000015 | 0.01 | 1 | 0.0000150000 |
| removing tmp table | 0.000006 | 0.00 | 1 | 0.0000060000 |
| cleaning up | 0.000004 | 0.00 | 1 | 0.0000040000 |
| end | 0.000004 | 0.00 | 1 | 0.0000040000 |
| closing tables | 0.000004 | 0.00 | 1 | 0.0000040000 |
| query end | 0.000003 | 0.00 | 1 | 0.0000030000 |
| System lock | 0.000003 | 0.00 | 1 | 0.0000030000 |
| logging slow query | 0.000002 | 0.00 | 1 | 0.0000020000 |
+--------------------+----------+-------+-------+--------------+
--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
mysql> select * from profiling limit 3,3G;
*************************** 1. row ***************************
QUERY_ID: 2
SEQ: 4
STATE: Table lock
DURATION: 0.000007
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: unknown function
SOURCE_FILE: lock.cc
SOURCE_LINE: 271
*************************** 2. row ***************************
QUERY_ID: 2
SEQ: 5
STATE: init
DURATION: 0.000010
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: unknown function
SOURCE_FILE: sql_select.cc
SOURCE_LINE: 2537
*************************** 3. row ***************************
QUERY_ID: 2
SEQ: 6
STATE: optimizing
DURATION: 0.000003
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: unknown function
SOURCE_FILE: sql_select.cc
SOURCE_LINE: 835
3 rows in set (0.00 sec)
ERROR:
No query specified
mysql>
--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
mysql> set profiling=off;
Query OK, 0 rows affected, 1 warning (0.00 sec)