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淺析MySQL讀寫分離與負載均衡實例教程

本教程我們來談談MySQL讀寫分離與負載均衡的原理及實現代碼實例,有需要的朋友可以參考學習一下。

MySQL 數據庫的讀寫分離和負載均衡一般是通過第三方軟件來實現的。 也可以通過mysql驅動程序來實現,如com.mysql.jdbc.ReplicationDriver。

詳細文檔參見:http://dev.mysql.com/doc/refman/5.5/en/connector-j-info.html

 代碼如下 復制代碼 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
    //
 
    conn.setReadOnly(true);
 
    ResultSet rs =
      conn.createStatement().executeQuery("SELECT a,b FROM alt_table");
 
     .......
  }
}

讀寫分離:

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對象,當設置這個connection.readOnly=true時,連接slave,當connection.readOnly=false時,連接master
負載均衡:

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.

問題:

讀寫分離時可能會碰到剛寫完master,再馬上到slave進行查詢的情況,而主從復制的時候有延遲,這時怎麼解決呢?有兩個辦法:

1. 比如增加頁面保存數據後馬上跳轉到列表頁面,這時可能出不來數據,因為復制還沒完成,這時可以在前台添加一些成功的提示,成功頁面等進行一些頁面跳轉延遲處理,讓服務器有時間去復制(復制延遲一般在毫秒級,而這種提示處理在秒級,所以時間上一般是足夠的)

2. 第1種辦法可能部分場景是可行的,但是有些場景要求比較高,需要實時的,這時可以在讀取的時候進行處理,強制從master中讀取,可以通過注解,加參數/標識等來指定從master讀取數據

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