本篇文章主要介绍了"事务隔离级别 mysql隔离级别"，主要涉及到事务隔离级别方面的内容，对于MySql感兴趣的同学可以参考一下：
原文链接
MySQL InnoDB事务的隔离级别有四级，默认是“可重复读”（REPEATABLE READ）。未提交读（READ UNCOMMITTED）。另...
t Session A Session B
|
| START TRANSACTION; START TRANSACTION;
|
| select * from actor;
+----------+------------+-----------+---------------------+| actor_id | first_name | last_name | last_update |
+----------+------------+-----------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 3 | t3 | t3 | 2016-06-16 15:18:33 |
| 4 | t0 | t0 | 2016-06-16 15:18:36 |
| 5 | t5 | t5 | 2016-06-16 16:03:51 |
+----------+------------+-----------+---------------------+
| insert into actor
| values (6,'t6','t6',now());
| COMMIT;
|
| select * from actor;
+----------+------------+-----------+---------------------+| actor_id | first_name | last_name | last_update |
+----------+------------+-----------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 3 | t3 | t3 | 2016-06-16 15:18:33 |
| 4 | t0 | t0 | 2016-06-16 15:18:36 |
| 5 | t5 | t5 | 2016-06-16 16:03:51 |
+----------+------------+-----------+---------------------+
|
| select * from actor lock in share mode;
+----------+------------+-----------+---------------------+| actor_id | first_name | last_name | last_update |
+----------+------------+-----------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 3 | t3 | t3 | 2016-06-16 15:18:33 |
| 4 | t0 | t0 | 2016-06-16 15:18:36 |
| 5 | t5 | t5 | 2016-06-16 16:03:51 |
| 6 | t6 | t6 | 2016-06-16 16:11:53 |
+----------+------------+-----------+---------------------+
|
| select * from actor for update;
+----------+------------+-----------+---------------------+| actor_id | first_name | last_name | last_update |
+----------+------------+-----------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 3 | t3 | t3 | 2016-06-16 15:18:33 |
| 4 | t0 | t0 | 2016-06-16 15:18:36 |
| 5 | t5 | t5 | 2016-06-16 16:03:51 |
| 6 | t6 | t6 | 2016-06-16 16:11:53 |
+----------+------------+-----------+---------------------+
|
| select * from actor;
+----------+------------+-----------+---------------------+| actor_id | first_name | last_name | last_update |
+----------+------------+-----------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 3 | t3 | t3 | 2016-06-16 15:18:33 |
| 4 | t0 | t0 | 2016-06-16 15:18:36 |
| 5 | t5 | t5 | 2016-06-16 16:03:51 |
+----------+------------+-----------+---------------------+
v
如果使用普通的读，会得到一致性的结果，如果使用了加锁的读，就会读到“最新的”“提交”读的结果。
本身，可重复读和提交读是矛盾的。在同一个事务里，如果保证了可重复读，就会看不到其他事务的提交，违背了提交读；如果保证了提交读，就会导致前后两次读到的结果不一致，违背了可重复读。
可以这么讲，InnoDB提供了这样的机制，在默认的可重复读的隔离级别里，可以使用加锁读去查询最新的数据。
http://dev.mysql.com/doc/refman/5.0/en/innodb-consistent-read.html
If you want to see the “freshest” state of the database, you should use either the READ COMMITTED isolation level or a locking read:
SELECT * FROM t_bitfly LOCK IN SHARE MODE;
结论：MySQL InnoDB的可重复读并不保证避免幻读，需要应用使用加锁读来保证。而这个加锁度使用到的机制就是next-key locks。
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以上就介绍了事务隔离级别 mysql隔离级别，包括了事务隔离级别方面的内容，希望对MySql有兴趣的朋友有所帮助。
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