Spring动态数据源-AbstractRoutingDataSource

一、分库分表思路

　1、垂直分表

　　拆分列。基于列进行。

　　根据业务耦合性，将关联度低的不同表存储在不同的数据库，与微服务类似，按照业务独立划分，每个微服务使用单独的一个数据库。也可将字段较多

的表拆分新建一张扩展表，将不常用或字段较大的字段拆分出去到扩展表中。

　　在字段很多的情况下（例如一个大表有100多个字段），通过"大表拆小表"，更便于开发与维护，也能避免跨页问题，MySQL底层是通过数据页存储的，

一条记录占用空间过大会导致跨页，造成额外的性能开销。另外数据库以行为单位将数据加载到内存中，这样表中字段长度较短且访问频率较高，内存能加

载更多的数据，命中率更高，减少了磁盘IO，从而提升了数据库性能。

　　优点：业务解耦清晰；高并发下，提升一定程度的IO，数据库连接数、单机硬件资源瓶颈。

　　缺点：部分表无法join，只能通过接口聚合，提升了开发复杂度；分布式事务处理复杂。

　2、水平分表

　　拆分行。基于行进行。

　　分为库内分表，分库分表，根据表内数据内在的逻辑关系，将同一个表按条件分散到多个数据库或多个表中，每张表中包含一部分数据，从而使单张表的数

据量变小。

　　库内分表只解决了单一表数据量过大的问题，但没有将表分布到不同机器的库上，因此对于减轻MySQL数据库的压力来说，帮助不是很大，大家还是竞争同

一个物理机的CPU、内存、网络IO，最好通过分库分表来解决。

　　优点：不存在单库数据量过大、高并发的性能瓶颈，提升系统稳定性和负载能力；应用端改造较小，不需要拆分业务模块。

　　缺点：跨分片的事务一致性难以保证；跨库的join关联性能较差；数据不易维护

二、Spring动态数据源实现分库

在分库分表的情况下，在执行SQL时选择连接不同的数据源（库）的思路：配置多个数据源加到动态数据源对象中，根据实际的情况动态切换到相应的数据源中。

如存放订单信息的有10个库，每个库中有100张表，根据用户的ID做分库分表。可以选择ID的某一位的值作为选择的第几个库，某两位的值作为对应的表名。

实现：在service中使用AOP拦截具有某个注解的方法，根据方法中的参数的用户信息，按照上面的规则指定要连接的数据源。

　　环境2.1.0.RELEASE，MySQL

1、所有的数据源信息配置：application.properties

#dataSource sharding
tvbss.jdbc.username=${config.tvbss.jdbc.username}
tvbss.jdbc.password=${config.tvbss.jdbc.password}
tvbss.jdbc.driver=${config.tvbss.jdbc.driver}
tvbss.jdbc.server00=${config.tvbss.jdbc.server00}
tvbss.jdbc.server01=${config.tvbss.jdbc.server01}
tvbss.jdbc.server02=${config.tvbss.jdbc.server02}
tvbss.jdbc.server03=${config.tvbss.jdbc.server03}
tvbss.jdbc.server04=${config.tvbss.jdbc.server04}
tvbss.jdbc.server05=${config.tvbss.jdbc.server05}
tvbss.jdbc.server06=${config.tvbss.jdbc.server06}
tvbss.jdbc.server07=${config.tvbss.jdbc.server07}
tvbss.jdbc.server08=${config.tvbss.jdbc.server08}
tvbss.jdbc.server09=${config.tvbss.jdbc.server09}

2、读取配置信息到属性类中

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.util.HashMap;
import java.util.Map;

/**
 * 数据源属性配置
 *
 * @author yangyongjie
 * @date 2019/9/27
 * @desc
 */
@Component
@ConfigurationProperties(prefix = "tvbss.jdbc")
public class ShardingProperties {
    private String username;
    private String password;
    private String driver;
    private String server00;
    private String server01;
    private String server02;
    private String server03;
    private String server04;
    private String server05;
    private String server06;
    private String server07;
    private String server08;
    private String server09;

    private Map<String, String> urlsMap = new HashMap<>();

    @PostConstruct
    public void initUrlList() {
        urlsMap.put("server00", server00);
        urlsMap.put("server01", server01);
        urlsMap.put("server02", server02);
        urlsMap.put("server03", server03);
        urlsMap.put("server04", server04);
        urlsMap.put("server05", server05);
        urlsMap.put("server06", server06);
        urlsMap.put("server07", server07);
        urlsMap.put("server08", server08);
        urlsMap.put("server09", server09);
    }

}

3、指定动态数据源的关键类

import com.xxx.common.bean.BaseShardedBean;
import com.xxx.config.datasource.prop.ShardingProperties;
import org.apache.commons.collections.MapUtils;
import org.apache.commons.dbcp.BasicDataSource;
import org.apache.commons.pool.impl.GenericObjectPool;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
import org.springframework.util.StringUtils;

import java.util.HashMap;
import java.util.Map;

/**
 * 动态数据源切换
 * 方式：配置多个数据源加到动态数据源对象中，根据实际的情况动态的切换到相应的数据源
 */
public class DynamicDataSource extends AbstractRoutingDataSource {

    private static Logger LOGGER = LoggerFactory.getLogger(DynamicDataSource.class);

    @Autowired
    private ShardingProperties shardingProperties;

    /**
     * 连接池分配的最大连接数
     */
    private int maxActive = GenericObjectPool.DEFAULT_MAX_ACTIVE;

    /**
     * 空闲时保留的最大连接数
     */
    private int maxIdle = GenericObjectPool.DEFAULT_MAX_IDLE;

    /**
     * 空闲时保留的最少连接数
     */
    private int minIdle = GenericObjectPool.DEFAULT_MIN_IDLE;

    /**
     * 当连接池没有空闲时等待的最大毫秒数，小于0表示无限期等待
     */
    private long maxWait = GenericObjectPool.DEFAULT_MAX_WAIT;
    /**
     * 连接池的初始连接数
     */
    private int initialSize = 0;

    /**
     * 返回数据源dataSource的key值，实现数据源切换的关键方法
     * 在determineTargetDataSource方法中根据key获取目标连接数据源
     *
     * @return
     */
    @Override
    protected Object determineCurrentLookupKey() {
        Object value = CurentDataSourceHolder.getCurentDataSource();
        if (StringUtils.isEmpty(value)) {
            value = BaseShardedBean.defaultKey();
        }
        return value;
    }

    /**
     * 启动时初始化所有的目标数据源
     */
    @Override
    public void afterPropertiesSet() {
        super.setTargetDataSources(buildDataSource());
        super.afterPropertiesSet();
    }

    /**
     * 根据配置文件的配置构建数据源
     *
     * @return
     */
    private Map<Object, Object> buildDataSource() {
        Map<Object, Object> dataSources = new HashMap<>(16);
        Map<String, String> urls = shardingProperties.getUrlsMap();
        if (MapUtils.isEmpty(urls)) {
            LOGGER.error("获取配置的数据库urls为空");
            return dataSources;
        }
        String driver = shardingProperties.getDriver();
        String username = shardingProperties.getUsername();
        String password = shardingProperties.getPassword();
        urls.forEach((key, value) -> {
            BasicDataSource dataSource = new BasicDataSource();
            dataSource.setDriverClassName(driver);
            dataSource.setUsername(username);
            dataSource.setPassword(password);
            dataSource.setUrl(value);
            dataSource.setMaxWait(maxWait);
            dataSource.setMaxIdle(maxIdle);
            dataSource.setMinIdle(minIdle);
            dataSource.setMaxActive(maxActive);
            dataSources.put(key, dataSource);
        });
        return dataSources;
    }

    /**
     * 数据源存放对象，用于动态切换用
     */
    public static class CurentDataSourceHolder {

        private static ThreadLocal<Object> holder = new ThreadLocal<>();

        /**
         * 设置当前线程的数据源
         *
         * @param source
         */
        public static void setCurentDataSource(Object source) {
            holder.set(source);
        }

        /**
         * 获取当前线程的数据源
         *
         * @return
         */
        public static Object getCurentDataSource() {
            return holder.get();
        }

        /**
         * 清楚数据源
         */
        public static void remove() {
            holder.remove();
        }
    }

    public int getMaxActive() {
        return maxActive;
    }

    public void setMaxActive(int maxActive) {
        this.maxActive = maxActive;
    }

    public int getMaxIdle() {
        return maxIdle;
    }

    public void setMaxIdle(int maxIdle) {
        this.maxIdle = maxIdle;
    }

    public int getMinIdle() {
        return minIdle;
    }

    public void setMinIdle(int minIdle) {
        this.minIdle = minIdle;
    }

    public long getMaxWait() {
        return maxWait;
    }

    public void setMaxWait(long maxWait) {
        this.maxWait = maxWait;
    }

    public int getInitialSize() {
        return initialSize;
    }

    public void setInitialSize(int initialSize) {
        this.initialSize = initialSize;
    }

}

　　afterPropertiesSet()方法初始化了所有的目标数据源

　　determineCurrentLookupKey()方法用来获取当前线程变量中指定的当前数据源的key，若没有，则使用默认数据源

AbstractRoutingDataSource ：

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {

    @Nullable
    private Map<Object, Object> targetDataSources; // 多个目标数据源

    @Nullable
    private Object defaultTargetDataSource; // 默认的目标数据源

    private boolean lenientFallback = true;

    private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();

    @Nullable
    private Map<Object, DataSource> resolvedDataSources;

    @Nullable
    private DataSource resolvedDefaultDataSource;

    /**
     * Specify the map of target DataSources, with the lookup key as key.
     * The mapped value can either be a corresponding {@link javax.sql.DataSource}
     * instance or a data source name String (to be resolved via a
     * {@link #setDataSourceLookup DataSourceLookup}).
     * <p>The key can be of arbitrary type; this class implements the
     * generic lookup process only. The concrete key representation will
     * be handled by {@link #resolveSpecifiedLookupKey(Object)} and
     * {@link #determineCurrentLookupKey()}.
     */
    public void setTargetDataSources(Map<Object, Object> targetDataSources) {
        this.targetDataSources = targetDataSources;
    }

    /**
     * Specify the default target DataSource, if any.
     * <p>The mapped value can either be a corresponding {@link javax.sql.DataSource}
     * instance or a data source name String (to be resolved via a
     * {@link #setDataSourceLookup DataSourceLookup}).
     * <p>This DataSource will be used as target if none of the keyed
     * {@link #setTargetDataSources targetDataSources} match the
     * {@link #determineCurrentLookupKey()} current lookup key.
     */
    public void setDefaultTargetDataSource(Object defaultTargetDataSource) {
        this.defaultTargetDataSource = defaultTargetDataSource;
    }

    /**
     * Specify whether to apply a lenient fallback to the default DataSource
     * if no specific DataSource could be found for the current lookup key.
     * <p>Default is "true", accepting lookup keys without a corresponding entry
     * in the target DataSource map - simply falling back to the default DataSource
     * in that case.
     * <p>Switch this flag to "false" if you would prefer the fallback to only apply
     * if the lookup key was {@code null}. Lookup keys without a DataSource
     * entry will then lead to an IllegalStateException.
     * @see #setTargetDataSources
     * @see #setDefaultTargetDataSource
     * @see #determineCurrentLookupKey()
     */
    public void setLenientFallback(boolean lenientFallback) {
        this.lenientFallback = lenientFallback;
    }

    /**
     * Set the DataSourceLookup implementation to use for resolving data source
     * name Strings in the {@link #setTargetDataSources targetDataSources} map.
     * <p>Default is a {@link JndiDataSourceLookup}, allowing the JNDI names
     * of application server DataSources to be specified directly.
     */
    public void setDataSourceLookup(@Nullable DataSourceLookup dataSourceLookup) {
        this.dataSourceLookup = (dataSourceLookup != null ? dataSourceLookup : new JndiDataSourceLookup());
    }

    @Override
    public void afterPropertiesSet() {
        if (this.targetDataSources == null) {
            throw new IllegalArgumentException("Property 'targetDataSources' is required");
        }
        this.resolvedDataSources = new HashMap<>(this.targetDataSources.size());
        this.targetDataSources.forEach((key, value) -> {
            Object lookupKey = resolveSpecifiedLookupKey(key);
            DataSource dataSource = resolveSpecifiedDataSource(value);
            this.resolvedDataSources.put(lookupKey, dataSource);
        });
        if (this.defaultTargetDataSource != null) {
            this.resolvedDefaultDataSource = resolveSpecifiedDataSource(this.defaultTargetDataSource);
        }
    }

    /**
     * Resolve the given lookup key object, as specified in the
     * {@link #setTargetDataSources targetDataSources} map, into
     * the actual lookup key to be used for matching with the
     * {@link #determineCurrentLookupKey() current lookup key}.
     * <p>The default implementation simply returns the given key as-is.
     * @param lookupKey the lookup key object as specified by the user
     * @return the lookup key as needed for matching
     */
    protected Object resolveSpecifiedLookupKey(Object lookupKey) {
        return lookupKey;
    }

    /**
     * Resolve the specified data source object into a DataSource instance.
     * <p>The default implementation handles DataSource instances and data source
     * names (to be resolved via a {@link #setDataSourceLookup DataSourceLookup}).
     * @param dataSource the data source value object as specified in the
     * {@link #setTargetDataSources targetDataSources} map
     * @return the resolved DataSource (never {@code null})
     * @throws IllegalArgumentException in case of an unsupported value type
     */
    protected DataSource resolveSpecifiedDataSource(Object dataSource) throws IllegalArgumentException {
        if (dataSource instanceof DataSource) {
            return (DataSource) dataSource;
        }
        else if (dataSource instanceof String) {
            return this.dataSourceLookup.getDataSource((String) dataSource);
        }
        else {
            throw new IllegalArgumentException(
                    "Illegal data source value - only [javax.sql.DataSource] and String supported: " + dataSource);
        }
    }

    @Override
    public Connection getConnection() throws SQLException {
        return determineTargetDataSource().getConnection();
    }

    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return determineTargetDataSource().getConnection(username, password);
    }

    @Override
    @SuppressWarnings("unchecked")
    public <T> T unwrap(Class<T> iface) throws SQLException {
        if (iface.isInstance(this)) {
            return (T) this;
        }
        return determineTargetDataSource().unwrap(iface);
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return (iface.isInstance(this) || determineTargetDataSource().isWrapperFor(iface));
    }

    /**
     * Retrieve the current target DataSource. Determines the
     * {@link #determineCurrentLookupKey() current lookup key}, performs
     * a lookup in the {@link #setTargetDataSources targetDataSources} map,
     * falls back to the specified
     * {@link #setDefaultTargetDataSource default target DataSource} if necessary.
     * @see #determineCurrentLookupKey()
     */
    protected DataSource determineTargetDataSource() {
        Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
        Object lookupKey = determineCurrentLookupKey();
        DataSource dataSource = this.resolvedDataSources.get(lookupKey);
        if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
            dataSource = this.resolvedDefaultDataSource;
        }
        if (dataSource == null) {
            throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
        }
        return dataSource;
    }

    /**
     * Determine the current lookup key. This will typically be
     * implemented to check a thread-bound transaction context.
     * <p>Allows for arbitrary keys. The returned key needs
     * to match the stored lookup key type, as resolved by the
     * {@link #resolveSpecifiedLookupKey} method.
     */
    @Nullable
    protected abstract Object determineCurrentLookupKey();

}

4、Spring容器中数据源配置类

import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;

/**
 * 数据源配置文件
 *
 * @author yangyongjie
 * @date 2019/9/25
 * @desc
 */
@Configuration
public class ShardingDataSourceConfig {

    private static final Logger LOGGER = LoggerFactory.getLogger(ShardingDataSourceConfig.class);

    /**
     * 数据源
     *
     * @return
     */
    @Bean
    public DynamicDataSource shardingDataSource() {
        DynamicDataSource dynamicDataSource = new DynamicDataSource();
        dynamicDataSource.setMaxActive(8);
        dynamicDataSource.setMaxIdle(2);
        dynamicDataSource.setMinIdle(1);
        dynamicDataSource.setMaxWait(60000);
        return dynamicDataSource;
    }

    @Bean
    public SqlSessionFactory shardingSqlSessionFactory() {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        // 扫描相关mapper文件
        PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        SqlSessionFactory sqlSessionFactory = null;
        try {
            sqlSessionFactoryBean.setMapperLocations(resolver.getResources("classpath:/mapper/**/*Mapper.xml"));
            sqlSessionFactoryBean.setDataSource(shardingDataSource());
//        sqlSessionFactoryBean.setConfigLocation();
            sqlSessionFactory = sqlSessionFactoryBean.getObject();
        } catch (Exception e) {
            LOGGER.error("创建SqlSessionFactory:"+e.getMessage(),e);
        }
        return sqlSessionFactory;
    }

    @Bean
    public SqlSessionTemplate shardingSqlSessionTemplate() {
        return new SqlSessionTemplate(shardingSqlSessionFactory());
    }

    /**
     * sharding数据源事务管理器
     *
     * @return
     */
    @Bean
    public DataSourceTransactionManager shardingTransactionManager() {
        return new DataSourceTransactionManager(shardingDataSource());
    }

}

　　

5、指定了默认数据源，提供 generateShardingKey 方法，用来根据当前bean分配库名，并保存在线程本地变量中，以及生成表名，为bean的tableIndex属性赋值

public abstract class BaseShardedBean {

    static String DEFAULT_SHARDING_SCHAME = "server";
    static String DEFAULT_SHARDING_INDEX = "00";

    public abstract Object dbKey();

    public abstract String tableKey();

    /**
     * 子类必须指定分片的key
     */
    public abstract Object genShardedKey();

    /**
     * 子类必须根据bean的映射选择表名
     */
    public abstract String genTableName();

    /**
     * 子类必须制定业务数据库类型
     */
    public abstract String genDbSchema();

    /**
     * 默认的库名,server00
     *
     * @return
     */
    public static Object defaultKey() {
        return DEFAULT_SHARDING_SCHAME + DEFAULT_SHARDING_INDEX;
    }

    /**
     * 生成库名和表名
     */
    public void generateShardingKey() {
        Object key = dbKey();
        key = StringUtils.isEmpty(key) ? defaultKey() : key;
        DynamicDataSource.CurentDataSourceHolder.setCurentDataSource(key);
        tableKey();
    }

}

6、具体的库表映射实体，继承了BaseShardedBean ，用户实体需继承它，以及顶一个公共的分库分表规则，即所有的实体类对应的分库分表规则都相同，不同的是库名前缀和表名前缀

**
 * 支持分片的Bean，只支持单表操作 required ${genShardedKey} 指定类型的分片key ${genTableName}  指定类型映射的表名
 **/
public abstract class ShardedMapperBean extends BaseShardedBean {

  @JsonIgnore
  protected String orderByClause;
  @JsonIgnore
  protected boolean distinct;
  @JsonIgnore
  protected String tableName;
  @JsonIgnore
  private String tableIndex;
  @JsonIgnore
  protected Object shardKey;

  public String getOrderByClause() {
    return orderByClause;
  }

  public void setOrderByClause(String orderByClause) {
    this.orderByClause = orderByClause;
  }

  public boolean isDistinct() {
    return distinct;
  }

  public void setDistinct(boolean distinct) {
    this.distinct = distinct;
  }

  public String getTableName() {
    return tableName;
  }

  public void setTableName(String tableName) {
    this.tableName = tableName;
  }

  public String getTableIndex() {
    return tableIndex;
  }

  public void setTableIndex(String tableIndex) {
    this.tableIndex = tableIndex;
  }

  @Override
  public Object dbKey() {
    String key = genShardedKey() == null ? null : String.valueOf(genShardedKey());
    if (StringUtils.isEmpty(key)) {
      return null;
    }
    return genDbSchema() + "0" + Integer.parseInt(getLastSub4to2(key)) / 10; // 库名为key倒数三四位除10取整，即倒数第四位的值，一共分10个库
  }

  @Override
  public String tableKey() {
    this.setTableName(genTableName());
    String key = genShardedKey() == null ? null : String.valueOf(genShardedKey());
    if (StringUtils.isEmpty(key)) {
      setTableIndex(genTableName());
      return null;
    } else {
      String tableIndex = genTableName() + "_" + getLastSub2(key); // 表名为倒数一二位的值，一共分100张表
      setTableIndex(tableIndex);
      return tableIndex;
    }
  }

  private static String getLastSub4to2(String key) {
    if (StringUtils.isEmpty(key) || key.length() < 4) {
      return "";
    }
    int keyLen = key.length();
    return key.substring(keyLen - 4, keyLen - 2);
  }

  private static String getLastSub2(String key) {
    if (StringUtils.isEmpty(key) || key.length() < 2) {
      return "";
    }
    int keyLen = key.length();
    return key.substring(keyLen - 2);
  }
}

如具体的实体继承ShardedMapperBean 之后重写的方法，自定义库名前缀和表名前缀，以及用什么作为分库分表的key

    @Override
    public Object genShardedKey() {
        return id;
    }

    @Override
    public String genTableName() {
        return "order";
    }

    @Override
    public String genDbSchema() {
        return "databaseNamePrefix";
    }

7、最后使用AOP拦截方法的执行，给DynamicDataSource中的静态内部类CurentDataSourceHolder中的线程本地变量指定实际连接的数据源即可。

import com.xxx.common.bean.BaseShardedBean;
import com.xxx.config.datasource.DynamicDataSource;
import org.apache.commons.lang3.StringUtils;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.stereotype.Component;
import org.springframework.transaction.annotation.Transactional;

import java.lang.reflect.Method;

/**
 * 事务注解的拦截器，为事务管理器为shardingTransactionManager的方法指定数据源
 *
 * @author yangyongjie
 * @date 2019/9/30
 * @desc
 */
@Aspect
@Component
public class TransactionAspect {

    private static final String SHARD_TRANSACTION_MANAGER = "shardingTransactionManager";

    @Pointcut("@annotation(org.springframework.transaction.annotation.Transactional)")
    private void transactionbPointCut() {
        // donothing
    }

    /**
     * 方法执行前的拦截,指定数据源
     * 因此如果需要动态指定数据源，则方法参数bean需要继承ShardedMapperBean并重写genShardedKey()、genTableName()和genDbSchema()
     *
     * @param joinPoint
     */
    @Before(value = "transactionbPointCut()")
    public void beforeTransaction(JoinPoint joinPoint) {
        // 获取方法上的注解
        MethodSignature methodSignature = (MethodSignature) joinPoint.getSignature();
        Method pointCutMethod = methodSignature.getMethod();
        Transactional ann = pointCutMethod.getAnnotation(Transactional.class);
        if (!StringUtils.equals(ann.value(), SHARD_TRANSACTION_MANAGER)) {
            return;
        }
        // 获取方法参数
        Object[] methodArgs = joinPoint.getArgs();
        for (Object args : methodArgs) {
            if (args instanceof BaseShardedBean) {
                ((BaseShardedBean) args).generateShardingKey();
                break;
            }
        }

    }

    /**
     * 方法执行后删除存放数据源key的线程本地变量
     */
    @After(value = "transactionbPointCut()")
    public void afterTransaction() {
        DynamicDataSource.CurentDataSourceHolder.remove();
    }
}

三、水平拆分数据分片规则

　　1、根据数值范围

　　　　按照时间区间或者ID区间来切分。例如：按日期将不同月甚至是日的数据分散到不同的库中；将userId为1~9999的记录分到第一个库，10000~20000的分到第二个库，以此类推。

　　2、根据数值取模

　　　　一般采用hash取模mod的切分方式，如将Order表根据userId字段切分到10个库中，余数为0的放到第一个库，余数为1的放到第二个库，依此类推。这样同一个用户的数据会分散到同一个库中。

end.