《Mysql學習解析Mysql Profiling的使用》要點：
本文介紹了Mysql學習解析Mysql Profiling的使用，希望對您有用。如果有疑問，可以聯系我們。
profiling是個很好用的mysql性能分析工具,今兒就來試驗下profiling的功能.感謝 有愛玫瑰的博文：
mysql 的 sql 性能分析器主要用途是顯示 sql 執行的整個過程中各項資源的使用情況.分析器可以更好的展示出不良 SQL 的性能問題所在.
下面我們舉例介紹一下MySQL SQL Profiler的使用方法：
首先,開啟 MySQL SQL Profiler
代碼如下:
mysql> SELECT @@profiling;
??? +-------------+
??? | @@profiling |
??? +-------------+
??? | 0 |
??? +-------------+
??? 1 row in set (0.00 sec)
??? mysql> SET profiling = 1;
??? Query OK, 0 rows affected (0.00 sec)
??? mysql> SELECT @@profiling;
??? +-------------+
??? | @@profiling |
??? +-------------+
??? | 1 |
??? +-------------+
1 row in set (0.00 sec)默認情況下 profiling 的值為 0 表示 MySQL SQL Profiler 處于 OFF 狀態,開啟 SQL 性能分析器后 profiling 的值為 1.
通過 sql 性能分析器,我們來對比一下 下列語句前后 2 次執行過程的差異,對我們了解 sql 的詳細執行過程是非常有幫助的.
代碼如下:
mysql> create table t_engines select * from t_engines1;
??? Query OK, 57344 rows affected (0.10 sec)
??? Records: 57344 Duplicates: 0 Warnings: 0
??? mysql> select count(*) from t_engines;
??? +----------+
??? | count(*) |
??? +----------+
??? | 57344 |
??? +----------+
??? 1 row in set (0.00 sec)
??? mysql> select count(*) from t_engines;
??? +----------+
??? | count(*) |
??? +----------+
??? | 57344 |
??? +----------+
??? 1 row in set (0.00 sec)
??? mysql> SHOW PROFILES;
??? +----------+------------+-------------------------------------------------+
??? | Query_ID | Duration | Query |
??? +----------+------------+-------------------------------------------------+
??? | 26 | 0.10213775 | create table t_engines select * from t_engines1 |
??? | 27 | 0.00032775 | select count(*) from t_engines |
??? | 28 | 0.00003850 | select count(*) from t_engines |
??? +----------+------------+-------------------------------------------------+
??? 15 rows in set (0.01 sec)
??? mysql> SHOW PROFILE FOR QUERY 27;
??? +--------------------------------+------------+
??? | Status | Duration |
??? +--------------------------------+------------+
??? | (initialization) | 0.00000425 |
??? | checking query cache for query | 0.00004050 |
??? | checking permissions | 0.00001050 |
??? | Opening tables | 0.00018250 |
??? | System lock | 0.00000450 |
??? | Table lock | 0.00001775 |
??? | init | 0.00001075 |
??? | optimizing | 0.00000550 |
??? | executing | 0.00002775 |
??? | end | 0.00000450 |
??? | query end | 0.00000325 |
??? | storing result in query cache | 0.00000400 |
??? | freeing items | 0.00000400 |
??? | closing tables | 0.00000500 |
??? | logging slow query | 0.00000300 |
??? +--------------------------------+------------+
??? 15 rows in set (0.00 sec)
??? mysql> SHOW PROFILE FOR QUERY 28;
??? +-------------------------------------+------------+
??? | Status | Duration |
??? +-------------------------------------+------------+
??? | (initialization) | 0.00000350 |
??? | checking query cache for query | 0.00000750 |
??? | checking privileges on cached query | 0.00000500 |
??? | checking permissions | 0.00000525 |
??? | sending cached result to client | 0.00001275 |
??? | logging slow query | 0.00000450 |
??? +-------------------------------------+------------+
??? 6 rows in set (0.00 sec) mysql> SELECT sum( FORMAT(DURATION, 6)) AS DURATION FROM INFORMATION_SCHEMA.PROFILING WHERE QUERY_ID =27 ORDER BY SEQ;
??? +----------+
??? | DURATION |
??? +----------+
??? | 0.000326 |
??? +----------+
??? 1 row in set (0.00 sec) mysql> SELECT sum( FORMAT(DURATION, 6)) AS DURATION FROM INFORMATION_SCHEMA.PROFILING WHERE QUERY_ID =28 ORDER BY SEQ;
??? +----------+
??? | DURATION |
??? +----------+
??? | 0.000039 |
??? +----------+
??? 1 row in set (0.00 sec)
從上面的例子中我們可以清晰的看出 2 次執行 count 語句的差別, SHOW PROFILE FOR QUERY 27 展現的是第一次 count 統計的執行過程,包含了 Opening tables 、 Table lock 等操作 .而 SHOW PROFILE FOR QUERY 28 展示了第二次 count 統計的執行過程 , 第二次 count 直接從查詢緩存中返回 count 統計結果,通過對比 2 次統計的總執行時間發現,緩存讀的速度接近物理讀的 10 倍.通過使用 SQL 性能分析器可以幫助我們對一些比較難以確定性能問題的 SQL 進行診斷,找出問題根源.
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