分析SQL執行帶來的開銷是優化SQL的重要手段。在MySQL數據庫中，可以通過配置profiling參數來啟用SQL剖析。該參數可以在全局和session級別來設置。對于全局級別則作用于整個MySQL實例，而session級別緊影響當前session。該參數開啟后，后續執行的SQL語句都將記錄其資源開銷，諸如IO，上下文切換，CPU，Memory等等。根據這些開銷進一步分析當前SQL瓶頸從而進行優化與調整。本文描述了如何使用MySQL profile，不涉及具體的樣例分析。

1、有關profile的描述

查看profiling系統變量

mysql> show variables like '%profil%';

+------------------------+-------+

| Variable_name??????????| Value |

+------------------------+-------+

| have_profiling???????? | YES?? |??#只讀變量,用于控制是否由系統變量開啟或禁用profiling;

| profiling??????????????| OFF?? |??#開啟或關閉SQL語句剖析功能;

| profiling_history_size | 15????|??#設置保留profiling的數目,缺省為15,范圍為0至100,為0時將禁用profiling;

+------------------------+-------+

3 rows in set (0.00 sec)

獲取profile的幫助

mysql> help profile;

Name: 'SHOW PROFILE'

Description:

Syntax:

SHOW PROFILE [type [, type] ... ]

[FOR QUERY n]

[LIMIT row_count [OFFSET offset]]

type:

ALL????????????????#顯示所有的開銷信息;

| BLOCK IO?????????? #顯示塊IO相關開銷;

| CONTEXT SWITCHES?? #上下文切換相關開銷;

| CPU????????????????#顯示CPU相關開銷信息;

| IPC????????????????#顯示發送和接收相關開銷信息;

| MEMORY???????????? #顯示內存相關開銷信息;

| PAGE FAULTS????????#顯示頁面錯誤相關開銷信息;

| SOURCE???????????? #顯示和Source_function,Source_file,Source_line相關的開銷信息;

| SWAPS??????????????#顯示交換次數相關開銷的信息;

2、開啟porfiling

啟用session級別的profiling

mysql> set profiling=1;

Query OK, 0 rows affected, 1 warning (0.00 sec)

驗證修改后的結果

mysql> show variables like '%profil%';

+------------------------+-------+

| Variable_name??????????| Value |

+------------------------+-------+

| have_profiling???????? | YES?? |

| profiling??????????????| ON????|

| profiling_history_size | 15????|

+------------------------+-------+

3 rows in set (0.00 sec)

發布SQL查詢

mysql> select * from zabbix.history_uint where clock<1488466329 limit 1;

查看當前session所有已產生的profile

mysql> show profiles;

+----------+------------+------------------------------------------------------------------+

| Query_ID | Duration?? | Query????????????????????????????????????????????????????????????|

+----------+------------+------------------------------------------------------------------+

|????????1 | 0.00044625 | show variables like '%profil%'?????????????????????????????????? |

|????????2 | 6.43230200 | select * from zabbix.history_uint where clock<1488466329 limit 1 |

+----------+------------+------------------------------------------------------------------+

2 rows in set, 1 warning (0.00 sec)

我們看到有2個warning，之前一個，現在一個

mysql> show warnings;

+---------+------+--------------------------------------------------------------------------------------------------------------+

| Level?? | Code | Message??????????????????????????????????????????????????????????????????????????????????????????????????????|

+---------+------+--------------------------------------------------------------------------------------------------------------+

| Warning | 1287 | 'SHOW PROFILES' is deprecated and will be removed in a future release. Please use Performance Schema instead |

+---------+------+--------------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

告警是說SHOW?PROFILES命令將來會被Performance?Schema替換掉。

3、獲取SQL語句的開銷信息

開啟profiling后，我們可以通過show?profile等方式查看，其實這些開銷信息被記錄到information_schema.profiling表中。注show?profile之類的語句不會被profiling，即自身不會產生Profiling。

我們下面的這個show?profile查看的是show?warnings產生的相應開銷。

mysq> show profile;

+----------------+----------+

| Status???????? | Duration |

+----------------+----------+

| starting?????? | 0.000141 |

| query end??????| 0.000058 |

| closing tables | 0.000014 |

| freeing items??| 0.001802 |

| cleaning up????| 0.000272 |

+----------------+----------+

如下面的查詢show?warnings被添加到profiles

mysql> show profiles;

+----------+------------+------------------------------------------------------------------+

| Query_ID | Duration?? | Query????????????????????????????????????????????????????????????|

+----------+------------+------------------------------------------------------------------+

|????????1 | 0.00041150 | show variables like '%profil%'?????????????????????????????????? |

|????????2 | 6.41118075 | select * from zabbix.history_uint where clock<1488466329 limit 1 |

|????????3 | 0.00003900 | show warnings????????????????????????????????????????????????????|

+----------+------------+------------------------------------------------------------------+

3 rows in set, 1 warning (0.00 sec)

獲取指定查詢的開銷(Druation表示持續時間)

mysql> show profile for query 2;

+----------------------+----------+

| Status?????????????? | Duration |

+----------------------+----------+

| starting???????????? | 0.000043 |

| checking permissions | 0.000004 |

| Opening tables?????? | 0.000014 |

| init???????????????? | 0.000019 |

| System lock??????????| 0.000004 |

| optimizing?????????? | 0.000009 |

| statistics?????????? | 0.000062 |

| preparing????????????| 0.000012 |

| executing????????????| 0.000002 |

| Sending data???????? | 6.410967 |

| end??????????????????| 0.000009 |

| query end????????????| 0.000005 |

| closing tables?????? | 0.000010 |

| freeing items????????| 0.000011 |

| cleaning up??????????| 0.000011 |

+----------------------+----------+

15 rows in set, 1 warning (0.00 sec)

Sending data：這個狀態的名稱很具有誤導性，所謂的“Sending data”并不是單純的發送數據，而是包括“收集 + 發送 數據”。

query end：表示語句執行完畢了，但是還有一些后續工作沒做完時的狀態。

freeing items：釋放查詢緩存里面的空間，如果是DML操作，所以相應的緩存里的記錄就無效了，所以需要有這一步做處理。

查看所有開銷

mysql> show profile all for query 2 ;

查看特定部分的開銷，如下為CPU部分的開銷

mysql> show profile cpu for query 2 ;

如下為MEMORY部分的開銷

mysql> show profile memory for query 2 ;

同時查看不同資源開銷

mysql> show profile block io,cpu for query 2;

4、INFORMATION_SCHEMA.PROFILING

上面已經看到了，show profile命令即將移除，所以可以直接去information_schema.profiling表查看，靈活度更大，其表結構信息如下：

mysql> desc information_schema.profiling;

+---------------------+--------------+------+-----+----------+-------+

| Field?????????????? | Type???????? | Null | Key | Default??| Extra |

+---------------------+--------------+------+-----+----------+-------+

| QUERY_ID????????????| int(20)??????| NO?? |???? | 0????????|?????? |

| SEQ???????????????? | int(20)??????| NO?? |???? | 0????????|?????? |

| STATE?????????????? | varchar(30)??| NO?? |???? |??????????|?????? |

| DURATION????????????| decimal(9,6) | NO?? |???? | 0.000000 |?????? |

| CPU_USER????????????| decimal(9,6) | YES??|???? | NULL???? |?????? |

| CPU_SYSTEM??????????| decimal(9,6) | YES??|???? | NULL???? |?????? |

| CONTEXT_VOLUNTARY?? | int(20)??????| YES??|???? | NULL???? |?????? |

| CONTEXT_INVOLUNTARY | int(20)??????| YES??|???? | NULL???? |?????? |

| BLOCK_OPS_IN????????| int(20)??????| YES??|???? | NULL???? |?????? |

| BLOCK_OPS_OUT?????? | int(20)??????| YES??|???? | NULL???? |?????? |

| MESSAGES_SENT?????? | int(20)??????| YES??|???? | NULL???? |?????? |

| MESSAGES_RECEIVED?? | int(20)??????| YES??|???? | NULL???? |?????? |

| PAGE_FAULTS_MAJOR?? | int(20)??????| YES??|???? | NULL???? |?????? |

| PAGE_FAULTS_MINOR?? | int(20)??????| YES??|???? | NULL???? |?????? |

| SWAPS?????????????? | int(20)??????| YES??|???? | NULL???? |?????? |

| SOURCE_FUNCTION???? | varchar(30)??| YES??|???? | NULL???? |?????? |

| SOURCE_FILE???????? | varchar(20)??| YES??|???? | NULL???? |?????? |

| SOURCE_LINE???????? | int(20)??????| YES??|???? | NULL???? |?????? |

+---------------------+--------------+------+-----+----------+-------+

18 rows in set (0.00 sec)

下面的SQL語句用于查詢query_id為2的SQL開銷，且按最大耗用時間倒序排列

mysql> set @query_id=2;

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???????? | 6.410967 | 100.00 |???? 1 | 6.4109670000 |

| statistics?????????? | 0.000062 |?? 0.00 |???? 1 | 0.0000620000 |

| starting???????????? | 0.000043 |?? 0.00 |???? 1 | 0.0000430000 |

| init???????????????? | 0.000019 |?? 0.00 |???? 1 | 0.0000190000 |

| Opening tables?????? | 0.000014 |?? 0.00 |???? 1 | 0.0000140000 |

| preparing????????????| 0.000012 |?? 0.00 |???? 1 | 0.0000120000 |

| cleaning up??????????| 0.000011 |?? 0.00 |???? 1 | 0.0000110000 |

| freeing items????????| 0.000011 |?? 0.00 |???? 1 | 0.0000110000 |

| closing tables?????? | 0.000010 |?? 0.00 |???? 1 | 0.0000100000 |

| optimizing?????????? | 0.000009 |?? 0.00 |???? 1 | 0.0000090000 |

| end??????????????????| 0.000009 |?? 0.00 |???? 1 | 0.0000090000 |

| query end????????????| 0.000005 |?? 0.00 |???? 1 | 0.0000050000 |

| System lock??????????| 0.000004 |?? 0.00 |???? 1 | 0.0000040000 |

| checking permissions | 0.000004 |?? 0.00 |???? 1 | 0.0000040000 |

| executing????????????| 0.000002 |?? 0.00 |???? 1 | 0.0000020000 |

+----------------------+----------+--------+-------+--------------+

15 rows in set (0.01 sec)

停止profile,可以設置profiling參數，或者在session退出之后,profiling會被自動關閉。

轉自：http://www.ywnds.com/?p=8677

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