serializable

实现方式：

2阶段加锁：读加锁，写加锁

这种加锁会导致 mvcc 失效，因为 select  * from xx也会加锁，select * from xx for update

RR

会话1

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

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

会话2：

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

mysql> insert into a select 3;
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> commit;
Query OK, 0 rows affected (0.04 sec)

会话1：

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



mysql> select * from a  for update;      
+------+
| a    |
+------+
| 1    |
| 2    |
| 3    |
+------+
3 rows in set (0.00 sec)

serializable级别:

会话1：

mysql> begin;   //事务未开始
Query OK, 0 rows affected (0.00 sec)

会话2：

mysql> begin;   
Query OK, 0 rows affected (0.05 sec)


mysql> select * from a;     //事务开始   //非一致性查询

会话1：

insert into a select 10;    等待事务2执行完毕   会话1事务才开始，第一条SQL语句,串行执行,非一致性查询也阻塞了会话1,串行级别 MVCC失效