## 1 分库分表
为什么要分库表呢？
1. 高并发。单库单表没法承受单并发。
2. 数据量大。磁盘空间问题
3. sql执行速度。单表太大
拆分的方式
* 水平拆分
* 大的数据量横向拆分成多个库表
* 垂直拆分
* 相关的业务拆分成独立的库表
## 2 为什么要用shardingjdbc
业界的技术
* tidb类似的数据库
* sharding-jdbc
* mycat proxy 层方案
* TDDL
* cobar proxy 层方案
* atlas proxy 层方案
sharding-jdbc社区活跃，使用方众多
官方地址：https://shardingsphere.apache.org/document/legacy/3.x/document/cn/quick-start/sharding-jdbc-quick-start/
## 3 sharding-jdbc的应用
提供的功能
* 分库分表
* 功能完善：聚合，分组，排序，limit，top查询，连表
* 支持内外连接查询
* 支持灵活的分表策略：等号，between，in多维度支持，自定义分表策略
* 基于hint强制分表路由
* 读写分离
* 柔性事务，TCC型事务
* 分布式主键
* 支持时间序列的id生成器
* 兼容性
* jpa，mybatis，jdbc-template
* 多种配置
* java,spring,yaml
概念
* 逻辑分表LogicTable
* 实际分表ActualTable
* 数据分片DataNode。数据分片的最小单元
* 动态分表。DynamicTable
* BindingTable，分表之间建立绑定关系
* shardingColumn分片字段
* shardingAlgorithm分片算法。支持range，hash，tag
* SQLHint。分片非sql决定的，支持灵活注入字段
基础应用
* 读写分离
* 分表
* 分库分表
读写分离的设置
```
<!-- 读写分离数据源 -->
<rdb:master-slave-data-source id="dataSource" master-data-source-ref="ds_0" slave-data-sources-ref="ds_1"/>
```
分库分表的设置
```
<rdb:strategy id="databaseShardingStrategyHouseLouDong" sharding-columns="city" algorithm-class="SingleKeyDbShardingAlgorithm"/>
<rdb:strategy id="tableShardingStrategyHouseLouDong" sharding-columns="id" algorithm-class="SingleKeyTableShardingAlgorithm"/>
<rdb:data-source id="dataSource">
<rdb:sharding-rule data-sources="ds_0, ds_1">
<rdb:table-rules>
<rdb:table-rule logic-table="user" actual-tables="user_${0..1}" database-strategy="databaseShardingStrategyHouseLouDong" table-strategy="tableShardingStrategyHouseLouDong">
<rdb:generate-key-column column-name="id"/>
</rdb:table-rule>
</rdb:table-rules>
</rdb:sharding-rule>
</rdb:data-source>
```
快速集成
```
<!-- mybatis plus 依赖 -->
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>${mybatis-plus-boot-starter.version}</version>
</dependency>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-annotation</artifactId>
<version>${mybatis-plus-annotation.version}</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-generator</artifactId>
<version>${mybatis-plus-generator.version}</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>${mysql-connector-java.version}</version>
</dependency>
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>${pagehelper.version}</version>
</dependency>
<dependency>
<groupId>org.apache.shardingsphere</groupId>
<artifactId>sharding-jdbc-spring-boot-starter</artifactId>
<version>${sharding-jdbc-spring-boot-starter.version}</version>
</dependency>
<dependency>
<groupId>org.apache.shardingsphere</groupId>
<artifactId>sharding-jdbc-spring-namespace</artifactId>
<version>${sharding-jdbc-spring-boot-starter.version}</version>
</dependency>
```
支持读写分离
```
#数据库
spring.shardingsphere.datasource.names=master,slave1
spring.shardingsphere.datasource.master.type=com.zaxxer.hikari.HikariDataSource
spring.shardingsphere.datasource.master.driver-class-name=com.mysql.cj.jdbc.Driver
spring.shardingsphere.datasource.master.jdbc-url=jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=Asia/Shanghai&allowMultiQueries=true&allowPublicKeyRetrieval=true
spring.shardingsphere.datasource.master.username=root
spring.shardingsphere.datasource.master.password=123456
spring.shardingsphere.datasource.master.pool-name=HikariPool-1
spring.shardingsphere.datasource.master.minimum-idle=1
spring.shardingsphere.datasource.master.maximum-pool-size=5
spring.shardingsphere.datasource.master.idle-timeout=600000
spring.shardingsphere.datasource.master.max-lifetime=1200000
spring.shardingsphere.datasource.master.connection-timeout=30000
spring.shardingsphere.datasource.master.connection-test-query=SELECT 1
spring.shardingsphere.datasource.slave1.type=com.zaxxer.hikari.HikariDataSource
spring.shardingsphere.datasource.slave1.driver-class-name=com.mysql.cj.jdbc.Driver
spring.shardingsphere.datasource.slave1.jdbc-url=jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=Asia/Shanghai&allowMultiQueries=true&allowPublicKeyRetrieval=true
spring.shardingsphere.datasource.slave1.username=root
spring.shardingsphere.datasource.slave1.password=123456
spring.shardingsphere.datasource.slave1.pool-name=HikariPool-2
spring.shardingsphere.datasource.slave1.minimum-idle=1
spring.shardingsphere.datasource.slave1.maximum-pool-size=5
spring.shardingsphere.datasource.slave1.idle-timeout=600000
spring.shardingsphere.datasource.slave1.max-lifetime=1200000
spring.shardingsphere.datasource.slave1.connection-timeout=30000
spring.shardingsphere.datasource.slave1.connection-test-query=SELECT 1
spring.shardingsphere.masterslave.load-balance-algorithm-type=round_robin
spring.shardingsphere.sharding.master-slave-rules.master.master-data-source-name=master
spring.shardingsphere.sharding.master-slave-rules.master.slave-data-source-names=slave1
```
