MySQL的隔离性测试

Posted 2022-11-29 adream307

在阅读本文前，请思考以下分别输出什么

操作序列1

1. 在数据库中存入 A=1
2. Client1启动一个事物T1
3. Client2启动一个事物T2
4. Client1 读取 A 的值 X1
5. Client2设置 A=2
6. Client2提交事物T2
7. Client1 读取 A 的值 X2
8. Client1提交事物T1
9. Client1 读取 A 的值 X3
   请问 X1 X2 X3 分别为什么值？

操作序列2

1. 在数据库中存入 A=1
2. Client1启动一个事物T1
3. Client2启动一个事物T2
4. Client2设置 A=2
5. Client2提交事物T2
6. Client1 读取 A 的值 X1
7. Client1提交事物T1
8. Client1 读取 A 的值 X2
   请问 X1 X2 分别为什么值？

---

启动 docker

使用docker 启动 mysql， 所有设置均采用默认配置

docker pull mysql:8
docker run --name mysql -e MYSQL_ROOT_PASSWORD=123456 -p 3306:3306  -d mysql:8

原始数据

mysql> create table t1(a int);
Query OK, 0 rows affected (0.05 sec)

mysql> insert t1 values(1);
Query OK, 1 row affected (0.02 sec)

mysql> select * from t1;
+------+
| a    |
+------+
|    1 |
+------+

链接 Client1 和Client2

mysql --user=root --password=123456  --port=3306 --host=127.0.0.1 --database=test

操作序列1

Client1 启动事物

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

Client2 启动事物

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

Client1 读取a的值

mysql> select * from t1;
+------+
| a    |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

Client2 设置a=2 并提交事物

mysql> update t1 set a=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.01 sec)

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

Client1 读取a 的值，并提交事物，然后再读取a的值

mysql> select * from t1;
+------+
| a    |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

因此在 mysql 中 X1=1, X2=1, X3=2

操作序列2

删除表格并重新插入数据

mysql> drop table t1;
Query OK, 0 rows affected (0.04 sec)

mysql> create table t1(a int);
Query OK, 0 rows affected (0.05 sec)

mysql> insert into t1 values(1);
Query OK, 1 row affected (0.02 sec)

mysql> select * from t1;
+------+
| a    |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

Client1 启动事物

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

Client2 启动事物

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

Client2 设置a=2 并提交事物

mysql> update t1 set a=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.02 sec)

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.01 sec)

Client1 读取a 的值，并提交事物，然后再读取a的值

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from t1;
+------+
| a    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

因此在 mysql 中 X1=2, X2=2