ShardingSphere学习专栏: 传送门
面对日益增加的系统访问量，数据库的吞吐量面临着巨大瓶颈。 对于同一时刻有大量并发读操作和较少写操作类型的应用系统来说，将数据库拆分为主库和从库，主库负责处理事务性的增删改操作，从库负责处理查询操作，能够有效的避免由数据更新导致的行锁，使得整个系统的查询性能得到极大的改善。
通过一主多从的配置方式，可以将查询请求均匀的分散到多个数据副本，能够进一步的提升系统的处理能力。 使用多主多从的方式，不但能够提升系统的吞吐量，还能够提升系统的可用性，可以达到在任何一个数据库宕机，甚至磁盘物理损坏的情况下仍然不影响系统的正常运行。
与将数据根据分片键打散至各个数据节点的水平分片不同，读写分离则是根据SQL语义的分析，将读操作和写操作分别路由至主库与从库。读写分离的数据节点中的数据内容是一致的，而水平分片的每个数据节点的数据内容却并不相同。
读写分离虽然可以提升系统的吞吐量和可用性，但同时也带来了数据不一致的问题。 这包括多个主库之间的数据一致性，以及主库与从库之间的数据一致性的问题，这需要我们开发时进行考虑。
sharding-jdbc与spring boot集成之后，通过配置我们就可以使用sharding-jdbc的功能
#数据源名称，多数据源以逗号分隔
spring.shardingsphere.datasource.names=master,slave0,slave1
spring.shardingsphere.datasource.master.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master.url=jdbc:mysql://localhost:3306/master
spring.shardingsphere.datasource.master.username=root
spring.shardingsphere.datasource.master.password=
spring.shardingsphere.datasource.slave0.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.slave0.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.slave0.url=jdbc:mysql://localhost:3306/slave0
spring.shardingsphere.datasource.slave0.username=root
spring.shardingsphere.datasource.slave0.password=
spring.shardingsphere.datasource.slave1.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.slave1.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.slave1.url=jdbc:mysql://localhost:3306/slave1
spring.shardingsphere.datasource.slave1.username=root
spring.shardingsphere.datasource.slave1.password=
spring.shardingsphere.masterslave.load-balance-algorithm-type=round_robin
spring.shardingsphere.masterslave.name=ms
spring.shardingsphere.masterslave.master-data-source-name=master
spring.shardingsphere.masterslave.slave-data-source-names=slave0,slave1
spring.shardingsphere.props.sql.show=true
1、首先定义数据源
先定义数据源的名称，多个以逗号分隔
spring.shardingsphere.datasource.names=master,slave0,slave1
然后定义数据源的连接信息
spring.shardingsphere.datasource.<data-source-name>.type= #数据库连接池类名称
spring.shardingsphere.datasource.<data-source-name>.driver-class-name= #数据库驱动类名
spring.shardingsphere.datasource.<data-source-name>.url= #数据库url连接
spring.shardingsphere.datasource.<data-source-name>.username= #数据库用户名
spring.shardingsphere.datasource.<data-source-name>.password= #数据库密码
spring.shardingsphere.datasource.<data-source-name>.xxx= #数据库连接池的其它属性
2、定义主从配置
从库负载均衡算法类型，可选值：ROUND_ROBIN，RANDOM。若load-balance-algorithm-class-name存在则忽略该配置
spring.shardingsphere.masterslave.load-balance-algorithm-type=round_robin
在读写分离场景下，主库用于处理写操作，从库用于处理读操作。当有多个从库时，需要使用负载均衡算法来决定将读请求发送到哪个从库上。
下面是ShardingSphere 常见的负载均衡算法
round_robin 算法
round_robin 算法是一种基本的负载均衡算法，它按照轮询的方式将请求平均分配给可用的从库。具体来说，它会依次将请求发送到从库列表中的每个从库，然后再从头开始循环。这样可以实现简单的负载均衡效果，确保每个从库都能够得到请求的处理机会。
random 算法
random 算法是一种随机的负载均衡算法，它从可用的从库列表中随机选择一个从库来处理请求。相对于 round_robin 算法，random 算法更具有不确定性，但也更容易产生负载不均衡的情况。
定义主从库的名称，这个名称是我们自定义的
spring.shardingsphere.masterslave.name=ms
在主从数据库架构中，主库用于处理写操作，从库用于处理读操作。为了实现读写分离，需要对主库和从库进行标识和配置。spring.shardingsphere.masterslave.master-data-source-name 属性用于指定主库的逻辑名称，spring.shardingsphere.masterslave.slave-data-source-names用于指定从库的逻辑名称，多个从库使用逗号分隔，名称对应我们数据源定义的名称
spring.shardingsphere.masterslave.master-data-source-name=master
spring.shardingsphere.masterslave.slave-data-source-names=slave0,slave1
是否在日志中显示 SQL 语句，默认为false，当将 spring.shardingsphere.props.sql.show 设置为 true 时，ShardingSphere 会在日志中打印执行的 SQL 语句，可以方便我们进行调试和监控。
spring.shardingsphere.props.sql.show=true
下面是使用数据分片和读写分离的配置
spring.shardingsphere.datasource.names=master0,master1,master0slave0,master0slave1,master1slave0,master1slave1
spring.shardingsphere.datasource.master0.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master0.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master0.url=jdbc:mysql://localhost:3306/master0
spring.shardingsphere.datasource.master0.username=root
spring.shardingsphere.datasource.master0.password=
spring.shardingsphere.datasource.master0slave0.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master0slave0.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master0slave0.url=jdbc:mysql://localhost:3306/master0slave0
spring.shardingsphere.datasource.master0slave0.username=root
spring.shardingsphere.datasource.master0slave0.password=
spring.shardingsphere.datasource.master0slave1.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master0slave1.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master0slave1.url=jdbc:mysql://localhost:3306/master0slave1
spring.shardingsphere.datasource.master0slave1.username=root
spring.shardingsphere.datasource.master0slave1.password=
spring.shardingsphere.datasource.master1.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master1.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master1.url=jdbc:mysql://localhost:3306/master1
spring.shardingsphere.datasource.master1.username=root
spring.shardingsphere.datasource.master1.password=
spring.shardingsphere.datasource.master1slave0.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master1slave0.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master1slave0.url=jdbc:mysql://localhost:3306/master1slave0
spring.shardingsphere.datasource.master1slave0.username=root
spring.shardingsphere.datasource.master1slave0.password=
spring.shardingsphere.datasource.master1slave1.type=org.apache.commons.dbcp.BasicDataSource
spring.shardingsphere.datasource.master1slave1.driver-class-name=com.mysql.jdbc.Driver
spring.shardingsphere.datasource.master1slave1.url=jdbc:mysql://localhost:3306/master1slave1
spring.shardingsphere.datasource.master1slave1.username=root
spring.shardingsphere.datasource.master1slave1.password=
spring.shardingsphere.sharding.tables.t_order.actual-data-nodes=ds$->{0..1}.t_order$->{0..1}
spring.shardingsphere.sharding.tables.t_order.table-strategy.inline.sharding-column=order_id
spring.shardingsphere.sharding.tables.t_order.table-strategy.inline.algorithm-expression=t_order$->{order_id % 2}
spring.shardingsphere.sharding.tables.t_order.key-generator.column=order_id
spring.shardingsphere.sharding.tables.t_order.key-generator.type=SNOWFLAKE
spring.shardingsphere.sharding.tables.t_order_item.actual-data-nodes=ds$->{0..1}.t_order_item$->{0..1}
spring.shardingsphere.sharding.tables.t_order_item.table-strategy.inline.sharding-column=order_id
spring.shardingsphere.sharding.tables.t_order_item.table-strategy.inline.algorithm-expression=t_order_item$->{order_id % 2}
spring.shardingsphere.sharding.tables.t_order_item.key-generator.column=order_item_id
spring.shardingsphere.sharding.tables.t_order_item.key-generator.type=SNOWFLAKE
spring.shardingsphere.sharding.binding-tables=t_order,t_order_item
spring.shardingsphere.sharding.broadcast-tables=t_config
spring.shardingsphere.sharding.default-database-strategy.inline.sharding-column=user_id
spring.shardingsphere.sharding.default-database-strategy.inline.algorithm-expression=master$->{user_id % 2}
#配置多个读写分离，配置了ds0和ds1数据源的读写分离
spring.shardingsphere.sharding.master-slave-rules.ds0.master-data-source-name=master0
spring.shardingsphere.sharding.master-slave-rules.ds0.slave-data-source-names=master0slave0, master0slave1
spring.shardingsphere.sharding.master-slave-rules.ds1.master-data-source-name=master1
spring.shardingsphere.sharding.master-slave-rules.ds1.slave-data-source-names=master1slave0, master1slave1