mysql 幻读

幻读（Phantom Read) 是指当用户读取某一范围的数据行时，B事务在该范围内插入了新行,当用户再读取该范围的数据行时,会发现有新的“幻影”行。InnoDB和Falcon存储引擎通 过多版本并发控制机制解决了幻读问题。

http://bbs.csdn.net/topics/360050896

http://narcissusoyf.iteye.com/blog/1637309

http://hudeyong926.iteye.com/blog/1490687

http://imysql.cn/2008_07_10_innodb_tx_isolation_and_lock_mode

http://www.cnblogs.com/zhaoyl/p/4121010.html

A事务读取了B事务已经提交的新增数据,此时 A 还没有提交，当前提交后,也就看到了

A事务

mysql> select * from test;
+----+----+
| a | b |
+----+----+
| 14 | 14 |
| 16 | 16 |
| 10 | 20 |
| 31 | 31 |
| 33 | 33 |
| 38 | 38 |
| 50 | 60 |
| 70 | 70 |
+----+----+
8 rows in set (0.00 sec)

事务B

mysql> insert into test (a,b) values(80,80);
Query OK, 1 row affected (0.00 sec)

事务A

mysql> select * from test;
+----+----+
| a | b |
+----+----+
| 14 | 14 |
| 16 | 16 |
| 10 | 20 |
| 31 | 31 |
| 33 | 33 |
| 38 | 38 |
| 50 | 60 |
| 70 | 70 |
+----+----+
8 rows in set (0.00 sec)

事务B

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

事务A 此时若不commit,是看不到事务B insert的数据的

mysql> select * from test;
+----+----+
| a | b |
+----+----+
| 14 | 14 |
| 16 | 16 |
| 10 | 20 |
| 31 | 31 |
| 33 | 33 |
| 38 | 38 |
| 50 | 60 |
| 70 | 70 |
+----+----+
8 rows in set (0.00 sec)

commit;

mysql> select * from test;
+----+----+
| a | b |
+----+----+
| 14 | 14 |
| 16 | 16 |
| 10 | 20 |
| 31 | 31 |
| 33 | 33 |
| 38 | 38 |
| 50 | 60 |
| 70 | 70 |
| 80 | 80 |
+----+----+
9 rows in set (0.00 sec)