负载均衡算法--平滑加权轮询法（Smooth Weight Round Robin）

川长思鸟来 2022-01-31 14:43 449阅读 0赞

接上一篇博文：[负载均衡算法–加权轮询法（Weight Round Robin）][Weight Round Robin]，接下来介绍平滑加权轮询法。

在加权轮询算法中我们讲到“从宏观的角度讲，权重高的服务器被访问的次数高一些，近似均衡；微观的角度讲，权重高的服务器会被连续访问到，看起来没有那么均衡。”，为了更好的解决均衡的问题，nginx 的作者提出了均衡加权轮询算法。

### 算法描述 ###

假设有 N 台服务器 S = \{S0, S1, S2, …, Sn\}，默认权重为 W = \{W0, W1, W2, …, Wn\}，当前权重为 CW = \{CW0, CW1, CW2, …, CWn\}。在该算法中有两个权重，默认权重表示服务器的原始权重，当前权重表示每次访问后重新计算的权重，当前权重的出初始值为默认权重值，当前权重值最大的服务器为 maxWeightServer，所有默认权重之和为 weightSum，服务器列表为 serverList，算法可以描述为：  
1、找出当前权重值最大的服务器 maxWeightServer；  
2、计算 \{W0, W1, W2, …, Wn\} 之和 weightSum；  
3、将 [maxWeightServer.CW][] = [maxWeightServer.CW][] \- weightSum；  
4、重新计算 \{S0, S1, S2, …, Sn\} 的当前权重 CW，计算公式为 [Sn.CW][] = [Sn.CW][] \+ Sn.Wn  
5、返回 maxWeightServer

假定我们现在有如下四台服务器：

<table> 
 <thead> 
  <tr> 
   <th>服务器地址</th> 
   <th>默认权重</th> 
   <th>当前权重</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>192.168.1.1</td> 
   <td>1</td> 
   <td>1</td> 
  </tr> 
  <tr> 
   <td>192.168.1.2</td> 
   <td>2</td> 
   <td>2</td> 
  </tr> 
  <tr> 
   <td>192.168.1.3</td> 
   <td>3</td> 
   <td>3</td> 
  </tr> 
  <tr> 
   <td>192.168.1.4</td> 
   <td>4</td> 
   <td>4</td> 
  </tr> 
 </tbody> 
</table>

### 代码实现 ###

1、服务器权重bean

package org.learn.loadbalance;
    
    import java.io.Serializable;
    
    public class SmoothWeightServer implements Serializable {
        private static final long serialVersionUID = 7246747589293111189L;
    
        private String server;
        private Integer originalWeight;
        private Integer currentWeight;
    
        public SmoothWeightServer(String server, Integer originalWeight, Integer currentWeight){
            this.server = server;
            this.originalWeight = originalWeight;
            this.currentWeight = currentWeight;
        }
        public Integer getOriginalWeight() {
            return originalWeight;
        }
    
        public void setOriginalWeight(Integer originalWeight) {
            this.originalWeight = originalWeight;
        }
    
        public Integer getCurrentWeight() {
            return currentWeight;
        }
    
        public void setCurrentWeight(Integer currentWeight) {
            this.currentWeight = currentWeight;
        }
    
        public String getServer() {
            return server;
        }
    
        public void setServer(String server) {
            this.server = server;
        }
    }

2、服务器管理类

package org.learn.loadbalance;
    
    import java.util.Map;
    import java.util.TreeMap;
    
    /**
     * @author zhibo
     * @date 2019/5/16 16:25
     */
    public class SmoothServerManager {
        public volatile static Map<String, SmoothWeightServer> serverMap = new TreeMap<>();
    
        static {
            serverMap.put("192.168.1.1", new SmoothWeightServer("192.168.1.1",1,1));
            serverMap.put("192.168.1.2", new SmoothWeightServer("192.168.1.2",2,2));
            serverMap.put("192.168.1.3", new SmoothWeightServer("192.168.1.3",3,3));
            serverMap.put("192.168.1.4", new SmoothWeightServer("192.168.1.4",4,4));
        }
    }

3、平滑加权轮询类

package org.learn.loadbalance;
    
    import java.util.*;
    
    /**
     * @author zhibo
     * @date 2019/5/16 16:28
     */
    public class SmoothWeightRoundRobin {
    
        public static String getServer() {
            Map<String, SmoothWeightServer> serverMap = new TreeMap<>(SmoothServerManager.serverMap);
    
            /// 原始权重之和
            Integer weightSum = 0;
            /// 最大当前权重对象
            SmoothWeightServer maxWeightServer = null;
    
            /// 计算最大当前权重对象，同时求原始权重之和
            Iterator<String> iterator = serverMap.keySet().iterator();
            while (iterator.hasNext()){
                SmoothWeightServer smoothWeightServer = serverMap.get(iterator.next());
                if(smoothWeightServer != null){
                    weightSum += smoothWeightServer.getOriginalWeight();
                    if(maxWeightServer == null){
                        maxWeightServer = smoothWeightServer;
                    }
                    if(smoothWeightServer.getCurrentWeight() > maxWeightServer.getCurrentWeight()){
                        maxWeightServer = smoothWeightServer;
                    }
                }
            }
    
            /**
             * 重新调整 currentWeight 权重：
             * maxWeightServer.currentWeight -= weightSum
             * 每个 smoothWeightServer.currentWeight += smoothWeightServer.originalWeight
             */
            if(maxWeightServer == null){
                return "";
            }
            maxWeightServer.setCurrentWeight(maxWeightServer.getCurrentWeight() - weightSum);
    
            iterator = serverMap.keySet().iterator();
            while (iterator.hasNext()){
                SmoothWeightServer smoothWeightServer = serverMap.get(iterator.next());
                if(smoothWeightServer != null){
                    smoothWeightServer.setCurrentWeight(smoothWeightServer.getCurrentWeight() + smoothWeightServer.getOriginalWeight());
                }
            }
    
            return maxWeightServer.getServer();
        }
    
        public static void main(String[] args) {
            for (int i = 0; i < 10; i++) {
                String server = getServer();
                System.out.println(server);
            }
        }
    }

执行 main 方法输出结果如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGliby5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70]  
文章内容仅代表个人观点，如有不正之处，欢迎批评指正，谢谢大家。

[Weight Round Robin]: https://zhibo.blog.csdn.net/article/details/90268868
[maxWeightServer.CW]: http://maxWeightServer.CW
[Sn.CW]: http://Sn.CW
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGliby5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70]: /images/20220131/279808313a7042aeb11e9123ca6923e0.png