MySQL SQL Tuning:Profile定位单条QUERY性能瓶颈

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MySQL SQL Tuning:Profile定位单条QUERY性能瓶颈

来源: 作者: 时间:2016-02-04 09:03 【

MySQL SQL Tuning:Profile定位单条QUERY性能瓶颈当生了病的query来就诊时,如果身为医生的我们胡庸医乱用虎狼药不仅于事无补,还浪费了大量的人力和时间成本,甚至会拖垮服务器所以,我
MySQL SQL Tuning:Profile定位单条QUERY性能瓶颈
 
当生了病的query来就诊时,如果身为医生的我们"胡庸医乱用虎狼药"
不仅于事无补,还浪费了大量的人力和时间成本,甚至会拖垮服务器
所以,我们在接受优化一条SQL,第一件事情便是要明白query病在哪里?
是IO?是CPU?只有明白瓶颈在哪里,方可对症下药,也才能药到病除
而MySQL QUERY Profiler是一个使用非常方便的QUERY诊断工具,5.0引入。5.1GA版嵌入
这个工具详细呈现了SQL在整个生命周期的每个动作,这和Oracle开启1046事件类似
我们可以很清晰地明白该SQL是在数据存取还是运算(排序或分组等)上花费得多
那么我们就不会很盲目地看到order by就去tuning sort buffer而忽略sorting result时间是如此之少
 
Profile语法:
[plain] 
SHOW PROFILE [type [, type] ... ]  
    [FOR QUERY n]  
    [LIMIT row_count [OFFSET offset]]  
  
type:  
    ALL  
  | BLOCK IO  
  | CONTEXT SWITCHES  
  | CPU  
  | IPC  
  | MEMORY  
  | PAGE FAULTS  
  | SOURCE  
  | SWAPS  

 

 
注解:
默认输出结果只会展示Status和Duration,我们可以指定type来扩展输出
我比较常用的是外加CPU和BLOCK IO来输出CPU和IO的负载,其实这些已经够了
 
默认profile是关闭的,通过profiling参数控制,为session级
开启:SET profiling=1
关闭:set profiling=0
查询:select @@profiling 
show profiles保存的query条数由参数profiling_history_size控制,默认是15,超过了会把前面的剔掉
[plain] 
> set profiling=1;  
  
mysql> select @@profiling;  
+-------------+  
| @@profiling |  
+-------------+  
|           1 |  
+-------------+  
  
mysql> select * from employees.t order by first_name;  
  
mysql> show profiles;  
+----------+------------+-----------------------------------------------+  
| Query_ID | Duration   | Query                                         |  
+----------+------------+-----------------------------------------------+  
|        1 | 0.21138800 | show create table employees.t                 |  
|        2 | 8.21691600 | select * from employees.t order by first_name |  
+----------+------------+-----------------------------------------------+  
2 rows in set (0.00 sec)  
  
mysql> show profile cpu,block io for query 2;  
+----------------------+----------+----------+------------+--------------+---------------+  
| Status               | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |  
+----------------------+----------+----------+------------+--------------+---------------+  
| starting             | 0.000160 | 0.000000 |   0.000000 |            0 |             0 |  
| checking permissions | 0.000026 | 0.000000 |   0.000000 |            0 |             0 |  
| Opening tables       | 0.000055 | 0.000000 |   0.000000 |            0 |             0 |  
| System lock          | 0.000033 | 0.000000 |   0.000000 |            0 |             0 |  
| init                 | 0.000050 | 0.000000 |   0.000000 |            0 |             0 |  
| optimizing           | 0.000026 | 0.000000 |   0.000000 |            0 |             0 |  
| statistics           | 0.000145 | 0.000000 |   0.000000 |            0 |             0 |  
| preparing            | 0.000118 | 0.000000 |   0.000000 |            0 |             0 |  
| executing            | 0.000011 | 0.000000 |   0.000000 |            0 |             0 |  
| Sorting result       | 2.838465 | 1.396087 |   1.140071 |            0 |             0 |  
| Sending data         | 0.928078 | 0.544034 |   0.056003 |            0 |             0 |  
| end                  | 0.000026 | 0.000000 |   0.000000 |            0 |             0 |  
| query end            | 0.000011 | 0.000000 |   0.000000 |            0 |             0 |  
| closing tables       | 0.000021 | 0.000000 |   0.000000 |            0 |             0 |  
| freeing items        | 4.449672 | 0.000000 |   0.000000 |            0 |             0 |  
| logging slow query   | 0.000014 | 0.000000 |   0.000000 |            0 |             0 |  
| cleaning up          | 0.000005 | 0.000000 |   0.000000 |            0 |             0 |  
+----------------------+----------+----------+------------+--------------+---------------+  
17 rows in set (0.00 sec)  

 

 
相同的信息我们还可以从information_schema里面输出,并且我们还可以对时间进行排序
因为Profile默认是按执行顺序排序的,而实际上我们更关心的是花费了多少时间,这才能方便知道哪些开销较大
[plain] 
mysql> SELECT STATE, FORMAT(DURATION, 6) AS DURATION  
    -> FROM INFORMATION_SCHEMA.PROFILING  
    -> WHERE QUERY_ID = 2 ORDER BY DURATION DESC;  
+----------------------+----------+  
| STATE                | DURATION |  
+----------------------+----------+  
| freeing items        | 4.449672 |  
| Sorting result       | 2.838465 |  
| Sending data         | 0.928078 |  
| starting             | 0.000160 |  
| statistics           | 0.000145 |  
| preparing            | 0.000118 |  
| Opening tables       | 0.000055 |  
| init                 | 0.000050 |  
| System lock          | 0.000033 |  
| end                  | 0.000026 |  
| optimizing           | 0.000026 |  
| checking permissions | 0.000026 |  
| closing tables       | 0.000021 |  
| logging slow query   | 0.000014 |  
| query end            | 0.000011 |  
| executing            | 0.000011 |  
| cleaning up          | 0.000005 |  
+----------------------+----------+  
17 rows in set (0.00 sec)  

 


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