mysql进阶-MYSQL逻辑架构和SQL执行流程

1.MYSQL逻辑架构

1.1 简洁的架构

典型的C/S架构，服务器端程序使用mysqld

简化为三层架构：

1. 连接层：客户端和服务端建立连接，客户端发送SQL至服务端；
2. SQL层（服务端）： 对SQL语句进行查询处理；与数据库文件的存储方式无关；
3. 存储引擎层： 与数据库文件打交道，负责数据库文件的存储和读取。

1.2 详细的架构

mysql 8.0之后删除了缓冲池，因为缓冲池的利用率很低但是需要占用空间，显得比较鸡肋。

2.SQL执行流程

2.1 详细的执行流程

2.2 简洁的执行流程

执行流程：

1. 先查询缓存【8.0之前】，如果缓存中存在直接返回结果；
2. 解析器：解析成解析树；
3. 优化器：对语法进行优化；
4. 执行引擎执行SQL语句并返回结果。

2.3 在控制台查看执行流程

2.3.1 打开流程记录设置

mysql中有一个系统变量@@profiling，默认是不记录SQL执行流程，设置成1时系统才会记录MySQL的执行过程。
查看@@profiling

// 查询方式一
mysql> select @@profiling;
+-------------+
| @@profiling |
+-------------+
|           0 |
+-------------+
1 row in set, 1 warning (0.00 sec)
// 查询方式二
mysql> show variables like 'profiling';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| profiling     | OFF   |
+---------------+-------+
1 row in set (0.00 sec)

设置@@profiling

mysql> set profiling = 1;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show variables like 'profiling';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| profiling     | ON    |
+---------------+-------+
1 row in set (0.00 sec)

2.3.2 随意执行一条sql

mysql> select * from book1;
+----+-------------+--------------------+------+
| id | category_id | book_name          | num  |
+----+-------------+--------------------+------+
|  1 |           3 | 平凡的世界         |  450 |
|  2 |           1 | 刺杀小说家         |  660 |
|  3 |           2 | 鲁滨孙漂流记       |  330 |
|  4 |           4 | 活着               |  200 |
+----+-------------+--------------------+------+
4 rows in set (0.00 sec)

2.3.3 查看刚才SQL的执行流程

mysql> show profile;
+----------------------+----------+
| Status               | Duration |
+----------------------+----------+
| starting             | 0.000053 |
| checking permissions | 0.000006 |
| Opening tables       | 0.000017 |
| init                 | 0.000016 |
| System lock          | 0.000007 |
| optimizing           | 0.000004 |
| statistics           | 0.000011 |
| preparing            | 0.000010 |
| executing            | 0.000003 |
| Sending data         | 0.000040 |
| end                  | 0.000004 |
| query end            | 0.000006 |
| closing tables       | 0.000006 |
| freeing items        | 0.000015 |
| cleaning up          | 0.000012 |
+----------------------+----------+
15 rows in set, 1 warning (0.00 sec)

多执行几条sql

mysql> select * from book1;
+----+-------------+--------------------+------+
| id | category_id | book_name          | num  |
+----+-------------+--------------------+------+
|  1 |           3 | 平凡的世界         |  450 |
|  2 |           1 | 刺杀小说家         |  660 |
|  3 |           2 | 鲁滨孙漂流记       |  330 |
|  4 |           4 | 活着               |  200 |
+----+-------------+--------------------+------+
4 rows in set (0.00 sec)

2.3.4 查看所有的sql执行过程

mysql> show profiles;
+----------+------------+---------------------------------+
| Query_ID | Duration   | Query                           |
+----------+------------+---------------------------------+
|        1 | 0.00140925 | show variables like 'profiling' |
|        2 | 0.00023625 | show tables                     |
|        3 | 0.00020700 | select * from book1             |
|        4 | 0.00025750 | select * from book1             |
|        5 | 0.00022700 | select * from book1             |
+----------+------------+---------------------------------+
5 rows in set, 1 warning (0.00 sec)

2.3.5 查看某条sql执行过程

mysql> show profile for query 2;
+----------------------+----------+
| Status               | Duration |
+----------------------+----------+
| starting             | 0.000047 |
| checking permissions | 0.000006 |
| checking permissions | 0.000003 |
| Opening tables       | 0.000035 |
| init                 | 0.000009 |
| System lock          | 0.000005 |
| optimizing           | 0.000004 |
| statistics           | 0.000010 |
| preparing            | 0.000009 |
| executing            | 0.000004 |
| checking permissions | 0.000051 |
| Sending data         | 0.000012 |
| end                  | 0.000003 |
| query end            | 0.000005 |
| closing tables       | 0.000003 |
| removing tmp table   | 0.000005 |
| closing tables       | 0.000003 |
| freeing items        | 0.000011 |
| cleaning up          | 0.000015 |
+----------------------+----------+
19 rows in set, 1 warning (0.00 sec)

2.3.6 查询sql的cup，io占用情况

mysql> show profile cpu,block io for query 5;
+----------------------+----------+----------+------------+--------------+---------------+
| Status               | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting             | 0.000067 | 0.000000 |   0.000062 |            0 |             0 |
| checking permissions | 0.000009 | 0.000000 |   0.000007 |            0 |             0 |
| Opening tables       | 0.000019 | 0.000000 |   0.000019 |            0 |             0 |
| init                 | 0.000016 | 0.000000 |   0.000015 |            0 |             0 |
| System lock          | 0.000007 | 0.000000 |   0.000007 |            0 |             0 |
| optimizing           | 0.000003 | 0.000000 |   0.000004 |            0 |             0 |
| statistics           | 0.000011 | 0.000000 |   0.000010 |            0 |             0 |
| preparing            | 0.000010 | 0.000000 |   0.000010 |            0 |             0 |
| executing            | 0.000003 | 0.000000 |   0.000003 |            0 |             0 |
| Sending data         | 0.000041 | 0.000000 |   0.000041 |            0 |             0 |
| end                  | 0.000003 | 0.000000 |   0.000003 |            0 |             0 |
| query end            | 0.000007 | 0.000000 |   0.000007 |            0 |             0 |
| closing tables       | 0.000006 | 0.000000 |   0.000006 |            0 |             0 |
| freeing items        | 0.000016 | 0.000000 |   0.000015 |            0 |             0 |
| cleaning up          | 0.000011 | 0.000000 |   0.000011 |            0 |             0 |
+----------------------+----------+----------+------------+--------------+---------------+
15 rows in set, 1 warning (0.00 sec)