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修改两处表达错误 #14

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Snailclimb merged 1 commit into from
Mar 27, 2021
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修改两处表达错误 #14

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6 changes: 3 additions & 3 deletions docs/d-1-mysql.md
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Expand Up @@ -183,7 +183,7 @@ select sql_no_cache count(*) from usr;

------

| 隔离级别 | 脏读 | 不可重复读 | 幻影读 |
| 隔离级别 | 脏读 | 不可重复读 | 幻读 |
| :--------------: | :--: | :--------: | :----: |
| READ-UNCOMMITTED | √ | √ | √ |
| READ-COMMITTED | × | √ | √ |
Expand Down Expand Up @@ -248,7 +248,7 @@ InnoDB 存储引擎在 **分布式事务** 的情况下一般会用到 **SERIALI

经典的数据库拆分方案，主库负责写，从库负责读；

#### 垂直分区
#### 垂直拆分

**根据数据库里面数据表的相关性进行拆分。** 例如，用户表中既有用户的登录信息又有用户的基本信息，可以将用户表拆分成两个单独的表，甚至放到单独的库做分库。

Expand All @@ -258,7 +258,7 @@ InnoDB 存储引擎在 **分布式事务** 的情况下一般会用到 **SERIALI
- **垂直拆分的优点：** 可以使得列数据变小，在查询时减少读取的Block数，减少I/O次数。此外，垂直分区可以简化表的结构，易于维护。
- **垂直拆分的缺点：** 主键会出现冗余，需要管理冗余列，并会引起Join操作，可以通过在应用层进行Join来解决。此外，垂直分区会让事务变得更加复杂；

#### 水平分区
#### 水平拆分

**保持数据表结构不变，通过某种策略存储数据分片。这样每一片数据分散到不同的表或者库中，达到了分布式的目的。 水平拆分可以支撑非常大的数据量。**

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