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注明了RR下幻读例子的发生原因 #2878

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注明了RR下幻读例子的发生原因 #2878

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2 changes: 2 additions & 0 deletions docs/database/mysql/transaction-isolation-level.md
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Expand Up @@ -105,6 +105,8 @@ SET [SESSION|GLOBAL] TRANSACTION ISOLATION LEVEL [READ UNCOMMITTED|READ COMMITTE

SQL 脚本 1 在第一次查询工资为 500 的记录时只有一条，SQL 脚本 2 插入了一条工资为 500 的记录，提交之后；SQL 脚本 1 在同一个事务中再次使用当前读查询发现出现了两条工资为 500 的记录这种就是幻读。

注：这里的幻读本质上是第一次快照读 + 第二次当前读 所产生的错位。在RR下，MVCC保证快照读不出现幻读，记录锁+间隙锁保证当前读不出现幻读。但快照读与当前读之间mysql不提供一致性保证。

#### 解决幻读的方法

解决幻读的方式有很多，但是它们的核心思想就是一个事务在操作某张表数据的时候，另外一个事务不允许新增或者删除这张表中的数据了。解决幻读的方式主要有以下几种：
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