MySQL学习笔记之SQL语句执行过程查看
文章目录
- 参数使能
- 查看最近一条SQL执行过程
- 查看profiling打开开后，所有SQL语句执行耗时
- 查看某一条SQL的执行过程
- 指定要查看的性能选项
- 查看所有性能选项
参数使能
以select语句为例，首先打开profile参数：
mysql> set profiling = 1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
然后执行两边下面的语句：
mysql> select * from employees;
查看最近一条SQL执行过程
可以通过show profile语句查看最近一条SQL的执行过程：
mysql> show profile;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000039 |
| checking permissions | 0.000004 |
| Opening tables | 0.000012 |
| init | 0.000014 |
| System lock | 0.000006 |
| optimizing | 0.000002 |
| statistics | 0.000008 |
| preparing | 0.000010 |
| executing | 0.000003 |
| Sending data | 0.000188 |
| end | 0.000004 |
| query end | 0.000006 |
| closing tables | 0.000008 |
| freeing items | 0.000104 |
| cleaning up | 0.000013 |
+----------------------+----------+
15 rows in set, 1 warning (0.00 sec)
可以看到一条SQL语句要经历上述15步。如果开启了SQL缓存且命中缓存的话，步骤会减少，但SQL缓存要求两条SQL必须完全一样才能命中，任何字符的更改(包括注释、空格等)都会导致缓存没命中，因此MySQL的缓存相当鸡肋，命中率很低。
查看profiling打开开后，所有SQL语句执行耗时
可以通过show profiles开启profiling后所有SQL语句的耗时：
mysql> show profiles;
+----------+------------+-------------------------+
| Query_ID | Duration | Query |
+----------+------------+-------------------------+
| 1 | 0.00070175 | select * from employees |
| 2 | 0.00041950 | select * from employees |
+----------+------------+-------------------------+
2 rows in set, 1 warning (0.00 sec)
查看某一条SQL的执行过程
可以通过show profile for query Query_ID查看：
mysql> show profile for query 1;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000036 |
| checking permissions | 0.000004 |
| Opening tables | 0.000012 |
| init | 0.000013 |
| System lock | 0.000006 |
| optimizing | 0.000002 |
| statistics | 0.000008 |
| preparing | 0.000355 |
| executing | 0.000006 |
| Sending data | 0.000169 |
| end | 0.000003 |
| query end | 0.000005 |
| closing tables | 0.000006 |
| freeing items | 0.000070 |
| cleaning up | 0.000007 |
+----------------------+----------+
15 rows in set, 1 warning (0.00 sec)
mysql> show profile for query 2;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000039 |
| checking permissions | 0.000004 |
| Opening tables | 0.000012 |
| init | 0.000014 |
| System lock | 0.000006 |
| optimizing | 0.000002 |
| statistics | 0.000008 |
| preparing | 0.000010 |
| executing | 0.000003 |
| Sending data | 0.000188 |
| end | 0.000004 |
| query end | 0.000006 |
| closing tables | 0.000008 |
| freeing items | 0.000104 |
| cleaning up | 0.000013 |
+----------------------+----------+
15 rows in set, 1 warning (0.00 sec)
指定要查看的性能选项
mysql> show profile CPU, block io;
+---------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+---------------+----------+----------+------------+--------------+---------------+
| starting | 0.000066 | 0.000000 | 0.000000 | NULL | NULL |
| freeing items | 0.000058 | 0.000000 | 0.000000 | NULL | NULL |
| cleaning up | 0.000004 | 0.000000 | 0.000000 | NULL | NULL |
+---------------+----------+----------+------------+--------------+---------------+
3 rows in set, 1 warning (0.00 sec)
查看所有性能选项
mysql> show profile all for query 1\G
*************************** 1. row ***************************
Status: starting
Duration: 0.000036
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: NULL
Source_file: NULL
Source_line: NULL
*************************** 2. row ***************************
Status: checking permissions
Duration: 0.000004
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: check_access
Source_file: sql_authorization.cc
Source_line: 802
*************************** 3. row ***************************
Status: Opening tables
Duration: 0.000012
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: open_tables
Source_file: sql_base.cc
Source_line: 5714
*************************** 4. row ***************************
Status: init
Duration: 0.000013
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: handle_query
Source_file: sql_select.cc
Source_line: 121
*************************** 5. row ***************************
Status: System lock
Duration: 0.000006
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: mysql_lock_tables
Source_file: lock.cc
Source_line: 323
*************************** 6. row ***************************
Status: optimizing
Duration: 0.000002
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: JOIN::optimize
Source_file: sql_optimizer.cc
Source_line: 151
*************************** 7. row ***************************
Status: statistics
Duration: 0.000008
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: JOIN::optimize
Source_file: sql_optimizer.cc
Source_line: 367
*************************** 8. row ***************************
Status: preparing
Duration: 0.000355
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: JOIN::optimize
Source_file: sql_optimizer.cc
Source_line: 475
*************************** 9. row ***************************
Status: executing
Duration: 0.000006
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: JOIN::exec
Source_file: sql_executor.cc
Source_line: 119
*************************** 10. row ***************************
Status: Sending data
Duration: 0.000169
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: JOIN::exec
Source_file: sql_executor.cc
Source_line: 195
*************************** 11. row ***************************
Status: end
Duration: 0.000003
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: handle_query
Source_file: sql_select.cc
Source_line: 199
*************************** 12. row ***************************
Status: query end
Duration: 0.000005
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: mysql_execute_command
Source_file: sql_parse.cc
Source_line: 4946
*************************** 13. row ***************************
Status: closing tables
Duration: 0.000006
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: mysql_execute_command
Source_file: sql_parse.cc
Source_line: 4998
*************************** 14. row ***************************
Status: freeing items
Duration: 0.000070
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: mysql_parse
Source_file: sql_parse.cc
Source_line: 5610
*************************** 15. row ***************************
Status: cleaning up
Duration: 0.000007
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: dispatch_command
Source_file: sql_parse.cc
Source_line: 1924
15 rows in set, 1 warning (0.00 sec)
举其中的一行为例：
*************************** 10. row ***************************
Status: Sending data
Duration: 0.000169
CPU_user: 0.000000
CPU_system: 0.000000
Context_voluntary: NULL
Context_involuntary: NULL
Block_ops_in: NULL
Block_ops_out: NULL
Messages_sent: NULL
Messages_received: NULL
Page_faults_major: NULL
Page_faults_minor: NULL
Swaps: NULL
Source_function: JOIN::exec
Source_file: sql_executor.cc
Source_line: 195
每一行数据就显示该步骤下的各个阶段的耗时，甚至源文件等信息。