浅析MySQL读写分离与负载均衡实例教程

发布:smiling　来源: PHP粉丝网　添加日期：2015-04-18 15:29:08　浏览: 评论：0　

MySQL 数据库的读写分离和负载均衡一般是通过第三方软件来实现的,也可以通过mysql驱动程序来实现,如com.mysql.jdbc.ReplicationDriver.

详细文档参见:http://dev.mysql.com/doc/refman/5.5/en/connector-j-info.html,代码如下:

import java.sql.Connection;

import java.sql.ResultSet;

import java.util.Properties;

import com.mysql.jdbc.ReplicationDriver;

public class ReplicationDriverDemo {

  public static void main(String[] args) throws Exception {

    ReplicationDriver driver = new ReplicationDriver();

    Properties props = new Properties();

    // We want this for failover on the slaves

    props.put("autoReconnect", "true");

    // We want to load balance between the slaves

    props.put("roundRobinLoadBalance", "true");

    props.put("user", "foo");

    props.put("password", "bar");

    //

    // Looks like a normal MySQL JDBC url, with a

    // comma-separated list of hosts, the first

    // being the 'master', the rest being any number

    // of slaves that the driver will load balance against

    //

    Connection conn =

        driver.connect("jdbc:mysql:replication://master,slave1,slave2,slave3/test",

            props);

    //

    // Perform read/write work on the master

    // by setting the read-only flag to "false"

    //

    conn.setReadOnly(false);

    conn.setAutoCommit(false);

    conn.createStatement().executeUpdate("UPDATE some_table ....");

    conn.commit();

    //

    // Now, do a query from a slave, the driver automatically picks one

    // from the list  --phpfensi.com

    //

    conn.setReadOnly(true);

    ResultSet rs =

      conn.createStatement().executeQuery("SELECT a,b FROM alt_table");

     .......

  }

}

读写分离:

jdbc:mysql:replication://master:3306,slave1:3306,slave2:3306/dbname

When using the following connection string: jdbc:mysql:replication://dbmaster:3306,dbslave1:3306,dbslave2:3306/dbname

dbmaster is used for all write connections as expected and dbslave1 is used for all read connections, but dbslave2 is never used. I would have expected distributed reads between dbslave1 and dbslave2.

原理是:ReplicationDriver生成代理的connection对象,当设置这个connection.readOnly=true时,连接slave,当connection.readOnly=false时,连接master

负载均衡:

jdbc:mysql:loadbalance://master:3306,slave1:3306,slave2:3306/dbname

When using the following connection string: jdbc:mysql:loadbalance://dbmaster:3306,dbslave1:3306,dbslave2:3306/dbname

connections are load-balanced between all three servers for both read and write connections.

问题:读写分离时可能会碰到刚写完master,再马上到slave进行查询的情况,而主从复制的时候有延迟,这时怎么解决呢？有两个办法.

1.比如增加页面保存数据后马上跳转到列表页面,这时可能出不来数据,因为复制还没完成，这时可以在前台添加一些成功的提示,成功页面等进行一些页面跳转延迟处理,让服务器有时间去复制,复制延迟一般在毫秒级,而这种提示处理在秒级,所以时间上一般是足够的.

2.第1种办法可能部分场景是可行的,但是有些场景要求比较高,需要实时的,这时可以在读取的时候进行处理,强制从master中读取,可以通过注解,加参数/标识等来指定从master读取数据.