1、算法
平滑加权轮询算法是一种改进的负载均衡算法，旨在解决传统加权轮询算法中存在的不均衡问题，该算法通过动态调整服务器权重，使请求分配更加均匀，从而提高系统的整体性能和稳定性。
2、算法步骤
平滑加权轮询算法包括以下步骤：计算所有服务器的默认权重总和；找出当前权重最大的服务器；将最大权重服务器的当前权重减去总权重；重新计算各服务器的当前权重并返回最大权重服务器。
3、示例分析
假设有四台服务器，其默认权重分别为1、2、3、4，初始状态下，各服务器的当前权重也为1、2、3、4，经过一次请求后，最大权重服务器（权重为4）的当前权重变为-3，其他服务器的当前权重分别增加其默认权重，最终得到新的当前权重分布。
4、代码实现
以下是使用Java实现的平滑加权轮询算法示例代码：
package org.learn.loadbalance;
import java.util.*;
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;
}
}
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));
}
}
public class SmoothWeightRoundRobin {
public static String getServer() {
Map<String, SmoothWeightServer> serverMap = new TreeMap<>(SmoothServerManager.serverMap);
int weightSum = getWeightSum(serverMap);
SmoothWeightServer maxWeightServer = null;
for (SmoothWeightServer server : serverMap.values()) {
if (maxWeightServer == null || server.getCurrentWeight() > maxWeightServer.getCurrentWeight()) {
maxWeightServer = server;
}
}
maxWeightServer.setCurrentWeight(maxWeightServer.getCurrentWeight() weightSum);
for (SmoothWeightServer server : serverMap.values()) {
server.setCurrentWeight(server.getCurrentWeight() + server.getOriginalWeight());
}
return maxWeightServer.getServer();
}
private static int getWeightSum(Map<String, SmoothWeightServer> serverMap) {
int sum = 0;
for (SmoothWeightServer server : serverMap.values()) {
sum += server.getOriginalWeight();
}
return sum;
}
}
5、相关问题与解答
问题1：平滑加权轮询算法如何确保请求分配的均衡性？
解答：平滑加权轮询算法通过在每次请求后动态调整服务器的当前权重，使得高权重服务器不会连续被选中多次，从而确保了请求分配的均衡性，这种动态调整机制有效地避免了某些服务器过载的问题，提高了系统的整体性能和稳定性。
问题2：为什么需要引入当前权重的概念？
解答：引入当前权重是为了在每次请求后对服务器的负载情况进行调整，当前权重反映了服务器在当前时刻的负载状态，通过减去总权重并重新计算，可以确保下次请求时选择到的服务器是当前负载相对较低的服务器，从而实现更均衡的负载分配。
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