为什么要使用读写分离
读写分离是互联网公司常用的技术方案,用来分摊数据库压力的。我们知道在一般的互联网项目中都是读多写少,这就导致数据库在大部分时候都在进行读操作,那么在高并发、高流量读的情况下,数据库的读操作就可能成为系统的性能瓶颈。
有的人可能会说,可以通过加缓存来解决数据库读的瓶颈,当然缓存也是一种有效的方案,可以迅速缓解数据库的压力。但有些场景我们不适合加缓存,比如数据变化比较频繁而我们对实时性要求比较高的场景下,使用缓存可以会导致业务上的逻辑存在问题。那我们只能通过查库来解决业务问题
本篇幅不会讲解数据库的主从搭建,重点讲解Springboot + mybatis代码层面的读写分离实现,下面我们进入正题
读写分离代码实现
1、配置多数据源
读写分离至少要包含一个写库、一个读库,那就会涉及到多数据源,数据库配置如下:
# 以一主一从为例,一主多从是类似的配置
mysql:
datasource:
master:
jdbc-url: jdbc:mysql://localhost:3306/testdb1
username: root
password: 123456
driver-class-name: com.mysql.jdbc.Driver
slave1:
jdbc-url: jdbc:mysql://localhost:3306/testdb2
username: root
password: 123456
driver-class-name: com.mysql.jdbc.Driver
2、继承spring的AbstractRoutingDataSource进行多数据源管理
public class MyRoutingDataSource extends AbstractRoutingDataSource {
@Nullable
@Override
protected Object determineCurrentLookupKey() {
return DBContextHolder.get();
}
}
3、数据源相关配置
@Configuration
public class DataSourceConfig {
@Bean(name = "masterDataSource")
@ConfigurationProperties(prefix = "mysql.datasource.master")
public DataSource masterDataSource(){
return DataSourceBuilder.create().build();
}
@Bean(name = "slaveDataSource")
@ConfigurationProperties(prefix = "mysql.datasource.slave1")
public DataSource slaveDataSource(){
return DataSourceBuilder.create().build();
}
@Bean(name = "myRoutingDataSource")
public DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
@Qualifier("slaveDataSource") DataSource slaveDataSource){
Map<Object,Object> targetDataSource = new HashMap<>();
targetDataSource.put(DBTypeEnum.MASTER,masterDataSource);
targetDataSource.put(DBTypeEnum.SLAVE,slaveDataSource);
MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();
myRoutingDataSource.setDefaultTargetDataSource(masterDataSource);
myRoutingDataSource.setTargetDataSources(targetDataSource);
return myRoutingDataSource;
}
}
// sqlSessionFactory和事务相关配置
@EnableTransactionManagement
@Configuration
public class MyBatisConfig {
@Resource(name = "myRoutingDataSource")
private DataSource myRoutingDataSource;
@Bean
public SqlSessionFactory sqlSessionFactory() throws Exception {
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(myRoutingDataSource);
sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/**/*.xml"));
return sqlSessionFactoryBean.getObject();
}
@Bean
public PlatformTransactionManager platformTransactionManager(){
return new DataSourceTransactionManager(myRoutingDataSource);
}
}
4、使用AOP进行数据源动态切换
public enum DBTypeEnum {
MASTER,SLAVE
}
//线程级别的数据源设置
public class DBContextHolder {
private static final ThreadLocal<DBTypeEnum> contextHolder = new ThreadLocal<>();
public static void set(DBTypeEnum dbType){
contextHolder.set(dbType);
}
public static DBTypeEnum get(){
return contextHolder.get();
}
public static void master(){
set(DBTypeEnum.MASTER);
System.out.println("切换到master");
}
public static void slave(){
set(DBTypeEnum.SLAVE);
System.out.println("切换到slave");
}
}
//定义AOP规则进行数据源的动态切换
@Component
@Aspect
public class DataSourceAop {
@Pointcut("@annotation(com.kxg.demo.annotation.ReadOnly)" +
"|| execution(* com.kxg.demo.mapper..*.find*(..))" +
"|| execution(* com.kxg.demo.mapper..*.get*(..))")
public void readPointcut(){
}
@Pointcut("!@annotation(com.kxg.demo.annotation.ReadOnly)" +
"&& execution(* com.kxg.demo.mapper..*.insert*(..))" +
"|| execution(* com.kxg.demo.mapper..*.update*(..))" +
"|| execution(* com.kxg.demo.mapper..*.delete*(..))")
public void writePointcut(){
}
@Before("readPointcut()")
public void read(){
DBContextHolder.slave();
}
@Before("writePointcut()")
public void write(){
DBContextHolder.master();
}
}
5、测试结果
@Data
public class User {
private Integer userId;
private String userName;
}
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.kxg.demo.mapper.UserMapper">
<select id="findAll" resultType="com.kxg.demo.model.User">
select * from tb_user
</select>
<insert id="insert" parameterType="com.kxg.demo.model.User">
insert into tb_user(user_id,user_name) values(#{userId},#{userName})
</insert>
</mapper>
@Mapper
public interface UserMapper {
List<User> findAll();
int insert(User user);
}
@Service
public class UserService {
@Autowired
private UserMapper userMapper;
@Transactional
public void insert(User user){
userMapper.insert(user);
}
@Transactional
public void save(){
}
//打上readOnly的注解,表示走读库
@ReadOnly
public List<User> findAll(){
return userMapper.findAll();
}
}
//写个测试方法测试一下
@RunWith(SpringRunner.class)
@SpringBootTest(classes = MultiDataSourceDemo.class)
@MapperScan(basePackages = "com.kxg.demo")
@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)
public class MultiDataSourceDemo {
@Autowired
private UserService userService;
@Test
public void testWrite(){
User user = new User();
Integer userId = new Random().nextInt();
user.setUserId(userId);
user.setUserName("user" + userId);
userService.insert(user);
}
@Test
public void testRead(){
userService.findAll();
}
}
分别运行testWrite()、testRead()方法
得到的结果如下: