MySQL RR隔离 读一致性

MySQL RR 模式下 事务隔离问题:

Session 1:
mysql> select * from test;
+------+------+
| id   | name |
+------+------+
| NULL | a    |
|    2 | b    |
|    3 | c    |
|    1 | a01  |
|    4 | a    |
|    4 | a    |
|    5 | c    |
+------+------+
7 rows in set (0.00 sec)

mysql> update test set name='a999' where id=1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from test;
+------+------+
| id   | name |
+------+------+
| NULL | a    |
|    2 | b    |
|    3 | c    |
|    1 | a999 |
|    4 | a    |
|    4 | a    |
|    5 | c    |
+------+------+
7 rows in set (0.00 sec)


Session 2:
mysql>  select * from test ;
+------+------+
| id   | name |
+------+------+
| NULL | a    |
|    2 | b    |
|    3 | c    |
|    1 | a01  |
|    4 | a    |
|    4 | a    |
|    5 | c    |
+------+------+
7 rows in set (0.00 sec)

mysql>  select * from test ;
+------+------+
| id   | name |
+------+------+
| NULL | a    |
|    2 | b    |
|    3 | c    |
|    1 | a999 |
|    4 | a    |
|    4 | a    |
|    5 | c    |
+------+------+
7 rows in set (0.00 sec)


此时没有开启事务,RR模式下 更新立即被看到



/****************************************************

Session 2开启事务:



SESSION 1:
mysql> update test set name='a0101' where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from test;
+------+-------+
| id   | name  |
+------+-------+
| NULL | a     |
|    2 | b     |
|    3 | c     |
|    1 | a0101 |
|    4 | a     |
|    4 | a     |
|    5 | c     |
+------+-------+
7 rows in set (0.00 sec)


此时在查看Session 2:

mysql>  select * from test ;
+------+------+
| id   | name |
+------+------+
| NULL | a    |
|    2 | b    |
|    3 | c    |
|    1 | a999 |
|    4 | a    |
|    4 | a    |
|    5 | c    |
+------+------+
7 rows in set (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)  ---需要手动提交事务

mysql>  select * from test ;
+------+-------+
| id   | name  |
+------+-------+
| NULL | a     |
|    2 | b     |
|    3 | c     |
|    1 | a0101 |
|    4 | a     |
|    4 | a     |
|    5 | c     |
+------+-------+
7 rows in set (0.00 sec)