寫在前面的話
爲什麼要分庫分表，這是基於mysql的b+樹的特性來的，當單表的數據量大了之後要維護一棵龐大的樹，這樣會使得增刪改查的性能大大降低。
本文基於一個普通Spring boot項目改造添加分庫分表依賴而來，具體可以看這一篇Spring boot整合mybatis generator實現自動生成代碼
從shardingsphere官網https://shardingsphere.apache.org/index_zh.html簡介來看好像改造分庫分表相當簡單，只需要引入maven依賴即可
可是它並沒有告訴你不同spring-boot版本要跟不同版本的sharding配合使用，比如我的demo初始化的時候spring-boot-starter-parent是2.2.6，shardingsphere是下面這個版本
<dependency>
<groupId>io.shardingsphere</groupId>
<artifactId>sharding-jdbc-spring-boot-starter</artifactId>
<version>3.0.0</version>
</dependency>
一啓動就報如下異常
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-04-21 05:16:09.869 ERROR 11072 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter :
***************************
APPLICATION FAILED TO START
***************************
Description:
The bean 'dataSource', defined in class path resource [io/shardingsphere/shardingjdbc/spring/boot/SpringBootConfiguration.class], could not be registered. A bean with that name has already been defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class] and overriding is disabled.
Action:
Consider renaming one of the beans or enabling overriding by setting spring.main.allow-bean-definition-overriding=true
Disconnected from the target VM, address: '127.0.0.1:65495', transport: 'socket'
Process finished with exit code 1
即使在yml文件添加了如下的配置也沒用
main:
allow-bean-definition-overriding: true
踩坑完畢，正文開始
org.springframework.boot使用2.0.3，sharding-jdbc使用3.0.0
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.3.RELEASE</version>
<relativePath/>
</parent>
<dependency>
<groupId>io.shardingsphere</groupId>
<artifactId>sharding-jdbc-spring-boot-starter</artifactId>
<version>3.0.0</version>
</dependency>
pom文件結構如下：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.3.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>mybatis-generator</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>mybatis-generator</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>io.shardingsphere</groupId>
<artifactId>sharding-jdbc-spring-boot-starter</artifactId>
<version>3.0.0</version>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.0.11</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>5.1.35</scope>
</dependency>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>1.3.0</version>
</dependency>
<!--分頁插件-->
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
<version>1.2.3</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<!--自動生成代碼插件-->
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.2</version>
<configuration>
<configurationFile>${basedir}/src/main/resources/generator/generatorConfig.xml</configurationFile>
<overwrite>true</overwrite>
<verbose>true</verbose>
</configuration>
</plugin>
</plugins>
</build>
</project>
application.yml
server:
port: 8080
sharding:
jdbc:
datasource:
names: test
# 數據庫test
test:
type: com.alibaba.druid.pool.DruidDataSource
driver-class-name: com.mysql.jdbc.Driver
url: jdbc:mysql://127.0.0.1:3306/test
username: root
password: 888888
config:
sharding:
props:
sql.show: true
tables:
user: #user表名
key-generator-column-name: id #主鍵
actual-data-nodes: test.user${0..1} #數據節點,均勻分佈
table-strategy: #分表策略
inline: #行內表達式
sharding-column: id
algorithm-expression: user${id % 2} #按模運算分配
mybatis:
mapper-locations: classpath:mapping/*.xml
type-aliases-package: com.example.mybatisgenerator.model
# 打印sql
logging:
level:
com.example.mybatisgenerator.dao : debug
需要注意的是，分庫分表的主鍵id要在代碼裏面生成，一般可以用雪花算法生成主鍵id，可參考舊文提及的分佈式ID生成方式之雪花算法 ，如果採用數據庫自增策略的話那麼不同的表它們的id肯定會衝突
建表語句
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`phone` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
執行測試
結果如下：
user0跟user1都有數據，user表是空的，可以理解爲user表是邏輯表，
以上這種是屬於單庫分表，當然也可以配置多個數據源，主要是yml文件上的寫法稍有差異。