在MySQL中，PROFILING功能提供了一种方式来分析SQL语句的执行时间，包括查询执行的各个阶段，如发送、解析、优化、执行等。这对于诊断性能问题非常有用。然而，需要注意的是，从MySQL 5.7.7版本开始，PROFILING功能被标记为已弃用（deprecated），并在以后的版本中完全移除。
使用PROFILING来查看SQL执行流程。以下是如何开启和使用PROFILING的步骤
1、开启Profiling
1.1、本次测试的环境
(root@localhost)[superdb]> status
--------------
mysql Ver 8.4.0 for Linux on x86_64 (MySQL Community Server - GPL)
Connection id: 11
Current database: superdb
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 8.4.0 MySQL Community Server - GPL
Protocol version: 10
Connection: Localhost via UNIX socket
Server characterset: utf8mb4
Db characterset: utf8mb4
Client characterset: utf8mb4
Conn. characterset: utf8mb4
UNIX socket: /tmp/mysql.sock
Binary data as: Hexadecimal
Uptime: 22 hours 13 min 49 sec
Threads: 2 Questions: 46 Slow queries: 0 Opens: 182 Flush tables: 3 Open tables: 101 Queries per second avg: 0.000
--------------
1.2、开启Profiling
(root@localhost)[superdb]> show variables like 'profiling';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| profiling | OFF |
+---------------+-------+
1 row in set (0.01 sec)
(root@localhost)[superdb]> SET profiling =1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
-- OR
SET profiling = on;
(root@localhost)[superdb]> show variables like 'profiling';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| profiling | ON |
+---------------+-------+
1 row in set (0.00 sec)
2、执行SQL查询
执行要分析的SQL查询。
(root@localhost)[superdb]> select * from dept;
+--------+------------+----------+
| deptno | dname | loc |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
+--------+------------+----------+
4 rows in set (0.00 sec)
3、查看查询的Profile
执行查询后，你可以通过以下命令查看所有查询的Profile
(root@localhost)[superdb]> show profiles;
+----------+------------+---------------------------------+
| Query_ID | Duration | Query |
+----------+------------+---------------------------------+
| 1 | 0.00288125 | show variables like '%profile%' |
| 2 | 0.00334150 | show variables like 'profiling' |
| 3 | 0.00147475 | select * from dept |
| 4 | 0.00265825 | show variables like 'profiling' |
| 5 | 0.00125125 | select * from dept |
+----------+------------+---------------------------------+
5 rows in set, 1 warning (0.00 sec)
这将列出所有已执行的查询及其查询编号（Query_ID）。
4、查看特定查询的详细Profile
选择你想要查看详细Profile的查询编号，然后使用以下命令：
(root@localhost)[superdb]> show profile for query 5;
+--------------------------------+----------+
| Status | Duration |
+--------------------------------+----------+
| starting | 0.000092 |
| Executing hook on transaction | 0.000028 |
| starting | 0.000032 |
| checking permissions | 0.000030 |
| Opening tables | 0.000257 |
| init | 0.000032 |
| System lock | 0.000071 |
| optimizing | 0.000028 |
| statistics | 0.000037 |
| preparing | 0.000037 |
| executing | 0.000096 |
| end | 0.000028 |
| query end | 0.000043 |
| waiting for handler commit | 0.000268 |
| closing tables | 0.000034 |
| freeing items | 0.000090 |
| cleaning up | 0.000050 |
+--------------------------------+----------+
17 rows in set, 1 warning (0.00 sec)
或者，你可以查看该查询的特定方面，如CPU_TIME、CONTEXT_SWITCHES等：
(root@localhost)[superdb]> SHOW PROFILE CPU, BLOCK IO FOR QUERY 5;
+--------------------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+--------------------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000092 | 0.000067 | 0.000025 | 0 | 0 |
| Executing hook on transaction | 0.000028 | 0.000020 | 0.000008 | 0 | 0 |
| starting | 0.000032 | 0.000023 | 0.000009 | 0 | 0 |
| checking permissions | 0.000030 | 0.000021 | 0.000008 | 0 | 0 |
| Opening tables | 0.000257 | 0.000126 | 0.000047 | 0 | 0 |
| init | 0.000032 | 0.000023 | 0.000009 | 0 | 0 |
| System lock | 0.000071 | 0.000051 | 0.000019 | 0 | 0 |
| optimizing | 0.000028 | 0.000020 | 0.000008 | 0 | 0 |
| statistics | 0.000037 | 0.000027 | 0.000010 | 0 | 0 |
| preparing | 0.000037 | 0.000027 | 0.000010 | 0 | 0 |
| executing | 0.000096 | 0.000070 | 0.000026 | 0 | 0 |
| end | 0.000028 | 0.000023 | 0.000009 | 0 | 0 |
| query end | 0.000043 | 0.000030 | 0.000012 | 0 | 0 |
| waiting for handler commit | 0.000268 | 0.000000 | 0.000148 | 0 | 0 |
| closing tables | 0.000034 | 0.000000 | 0.000034 | 0 | 0 |
| freeing items | 0.000090 | 0.000000 | 0.000090 | 0 | 0 |
| cleaning up | 0.000050 | 0.000000 | 0.000049 | 0 | 0 |
+--------------------------------+----------+----------+------------+--------------+---------------+
17 rows in set, 1 warning (0.00 sec)
5、总结
由于PROFILING在MySQL 5.7.7之后被弃用，并在未来MySQL的版本中完全移除，你需要使用其他工具或方法来进行性能分析。
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Performance Schema：MySQL 5.5及更高版本引入了Performance Schema，这是一个功能强大的性能监控和诊断框架。你可以使用它来收集关于服务器执行情况的详细数据。
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EXPLAIN和EXPLAIN ANALYZE：EXPLAIN语句可以用来查看MySQL如何执行SELECT语句，包括如何连接表和选择索引。MySQL 8.0.18引入了EXPLAIN ANALYZE，它提供了查询执行计划的详细运行时统计信息。
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慢查询日志：通过配置MySQL的慢查询日志，你可以捕获执行时间超过指定阈值的所有查询。这对于识别性能瓶颈非常有用。
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第三方工具：如Percona Toolkit、MySQL Workbench等，这些工具提供了图形界面和额外的功能来帮助你分析和优化MySQL查询。
总的来说，虽然PROFILING是一个有用的工具，但随着MySQL的发展，你应该考虑使用更现代和强大的性能分析工具。
