MYSQL SHOW PROFILE（剖析報告）的檢視

前言：SHOW PROFIL命令是mysql提供可以用來分析當前會話中語句執行的資源消耗情況。可以用於SQL的調優的測量。

一、引數的開啟和關閉設定

1.1  引數的檢視

預設情況下，引數處於關閉狀態，並儲存最近15次的執行結果

mysql>  show variables like 'profiling%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| profiling              | OFF   |
| profiling_history_size | 15    |
+------------------------+-------+
2 rows in set
 

1.2 引數的開啟和關閉（引數為會話級引數，只對當前會話有效）

開啟操作如下：

mysql> SET profiling=1;或 SET profiling=on;

mysql>  SET profiling=on;
Query OK, 0 rows affected
 
mysql>  show variables like 'profiling%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| profiling              | ON    |
| profiling_history_size | 15    |
+------------------------+-------+
2 rows in set
 

關閉的操作：
mysql> SET profiling=0;或 SET profiling=off;

 

二、操作步驟

2.1 進行開啟操作： SET profiling=on;

2.2 執行相應的SQL語句；

2.3 檢視總體結果：show profiles;

2.4 檢視詳細的結果：SHOW PROFILE FOR QUERY n，這裡的n就是對應SHOW PROFILES輸出中的Query_ID；

mysql> show profiles;
 
+----------+------------+------------------------------------+
| Query_ID | Duration   | Query                              |
+----------+------------+------------------------------------+
|        1 | 0.00077425 | select count(*) from tab_user_info |
|        2 |  0.0013575 | select count(*) from tab_tel_area  |
|        3 |     9.7E-5 | select count(*) from tab_tel_area  |
|        4 |   0.005193 | show variables like 'profiling%'   |
+----------+------------+------------------------------------+
4 rows in set
 
mysql> show profile for query 2;
+--------------------------------+----------+
| Status                         | Duration |
+--------------------------------+----------+
| starting                       | 2E-5     |
| checking query cache for query | 4.7E-5   |
| Opening tables                 | 0.001163 |
| System lock                    | 4E-6     |
| Table lock                     | 4.1E-5   |
| init                           | 1.6E-5   |
| optimizing                     | 6E-6     |
| executing                      | 1.4E-5   |
| end                            | 5E-6     |
| query end                      | 3E-6     |
| freeing items                  | 3.1E-5   |
| storing result in query cache  | 5E-6     |
| logging slow query             | 3E-6     |
| cleaning up                    | 2E-6     |
+--------------------------------+----------+
14 rows in set

說明：報告給出了查詢執行的每個步驟及花費的時間，當語句是很簡單的一次執行的時候，可以很清楚的看出語句每個順序花費的時間，但是當語句是巢狀迴圈等操作的時候，看這個報告就會變得很痛苦，因此整理了以下語句對相同型別的操作進行彙總，指令碼如下：

mysql> SET @QUERY_ID=1;

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;

總結：這個工具又讓我聯想到了oracle的autotrace工具，如果有相應的執行計劃一起帶出來，那麼對語句的調優幫助將更大；