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最近想詳細瞭解下dubbo負載均衡，本來想從網上找些資料輔助學習，沒想到這些資料都是比較舊的，比如說dubbo負載均衡存在的一些問題，最新版本(2.7.0)的其實已經修復了。所以想著還是得自己詳細看下原始碼，並寫一下總結，一方面便於日後的回顧，同時也希望能夠對大家有一些幫助。
正文開始
dubbo負載均衡，說白了就是從一堆的服務提供者之中，選擇一個來處理消費者的服務請求。我們看下LoadBalance的介面類
@SPI(RandomLoadBalance.NAME)
public interface LoadBalance {
/**
* select one invoker in list.
*
* @param invokers invokers.
* @param url refer url
* @param invocation invocation.
* @return selected invoker.
*/
@Adaptive("loadbalance")
<T> Invoker<T> select(List<Invoker<T>> invokers, URL url, Invocation invocation) throws RpcException;
}複製程式碼從程式碼中看出，負載均衡主要是從服務提供者列表中，選擇一個。這個介面有一個抽象類的實現。
public abstract class AbstractLoadBalance implements LoadBalance {
static int calculateWarmupWeight(int uptime, int warmup, int weight) {
int ww = (int) ((float) uptime / ((float) warmup / (float) weight));
return ww < 1 ? 1 : (ww > weight ? weight : ww);
}
@Override
public <T> Invoker<T> select(List<Invoker<T>> invokers, URL url, Invocation invocation) {
if (invokers == null || invokers.isEmpty()) {
return null;
}
if (invokers.size() == 1) { //當只有一個invoker時，直接返回
return invokers.get(0);
}
//選擇一個invoker
return doSelect(invokers, url, invocation);
}
//具體的負載均衡策略由子類來實現
protected abstract <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation);
//權重方法
protected int getWeight(Invoker<?> invoker, Invocation invocation) {
//如果有配置，直接讀取配置
int weight = invoker.getUrl().getMethodParameter(invocation.getMethodName(), Constants.WEIGHT_KEY, Constants.DEFAULT_WEIGHT);
if (weight > 0) {
long timestamp = invoker.getUrl().getParameter(Constants.REMOTE_TIMESTAMP_KEY, 0L);
if (timestamp > 0L) {
int uptime = (int) (System.currentTimeMillis() - timestamp);
int warmup = invoker.getUrl().getParameter(Constants.WARMUP_KEY, Constants.DEFAULT_WARMUP);
if (uptime > 0 && uptime < warmup) {
weight = calculateWarmupWeight(uptime, warmup, weight);
}
}
}
return weight;
}
}複製程式碼這個抽象類很簡單，主要就是額外增加了一個獲取權重的方法。我們看下具體的實現類。
從截圖中可以看出，dubbo的負載均衡一共有4種。分別為:
1、一致性hash ConsistentHashLoadBalance
2、最小活躍數 LeastActiveLoadBalance
3、隨機 RandomLoadBalance
4、輪詢 RoundRobinLoadBalance
本文講下輪詢，先來看下核心程式碼(後續用演示圖來描述步驟)
public class RoundRobinLoadBalance extends AbstractLoadBalance {
public static final String NAME = "roundrobin";
private static int RECYCLE_PERIOD = 60000;
//這個類主要是記錄每個提供者的權重資訊
protected static class WeightedRoundRobin {
private int weight; //權重
private AtomicLong current = new AtomicLong(0); //每次獲得執行機會後，權重值
private long lastUpdate; //暫時先忽略
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
current.set(0);
}
public long increaseCurrent() {
return current.addAndGet(weight);
}
public void sel(int total) {
current.addAndGet(-1 * total);
}
public long getLastUpdate() {
return lastUpdate;
}
public void setLastUpdate(long lastUpdate) {
this.lastUpdate = lastUpdate;
}
}
private ConcurrentMap<String, ConcurrentMap<String, WeightedRoundRobin>> methodWeightMap = new ConcurrentHashMap<String, ConcurrentMap<String, WeightedRoundRobin>>();
private AtomicBoolean updateLock = new AtomicBoolean();
/**
* get invoker addr list cached for specified invocation
* <p>
* <b>for unit test only</b>
*
* @param invokers
* @param invocation
* @return
*/
protected <T> Collection<String> getInvokerAddrList(List<Invoker<T>> invokers, Invocation invocation) {
String key = invokers.get(0).getUrl().getServiceKey() + "." + invocation.getMethodName();
Map<String, WeightedRoundRobin> map = methodWeightMap.get(key);
if (map != null) {
return map.keySet();
}
return null;
}
@Override
protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
//每一個方法對應自己的一套快取（一個map）
String key = invokers.get(0).getUrl().getServiceKey() + "." + invocation.getMethodName();
//每個map中快取著每個提供者對應的權重狀態
ConcurrentMap<String, WeightedRoundRobin> map = methodWeightMap.get(key);
if (map == null) {
methodWeightMap.putIfAbsent(key, new ConcurrentHashMap<String, WeightedRoundRobin>());
map = methodWeightMap.get(key);
}
int totalWeight = 0;
long maxCurrent = Long.MIN_VALUE;
long now = System.currentTimeMillis();
Invoker<T> selectedInvoker = null;
WeightedRoundRobin selectedWRR = null;
//迴圈服務提供者列表
for (Invoker<T> invoker : invokers) {
String identifyString = invoker.getUrl().toIdentityString();
//獲取服務提供者對應的權重狀態
WeightedRoundRobin weightedRoundRobin = map.get(identifyString);
int weight = getWeight(invoker, invocation); //權重從配置中讀取。沒有配置預設相等
if (weight < 0) {
weight = 0;
}
//權重狀態為空，則需要新建
if (weightedRoundRobin == null) {
weightedRoundRobin = new WeightedRoundRobin();
weightedRoundRobin.setWeight(weight);
map.putIfAbsent(identifyString, weightedRoundRobin);
weightedRoundRobin = map.get(identifyString);
}
if (weight != weightedRoundRobin.getWeight()) {
//weight changed 權重變更
weightedRoundRobin.setWeight(weight);
}
//每次迴圈，服務提供者的當前權重值都會加上權重值
long cur = weightedRoundRobin.increaseCurrent();
weightedRoundRobin.setLastUpdate(now);
//這個if程式碼主要是為了找到這組服務提供者列表中當前權重值最大的
if (cur > maxCurrent) {
maxCurrent = cur;
selectedInvoker = invoker;
selectedWRR = weightedRoundRobin;
}
totalWeight += weight; //一個迴圈結束，服務列表不變，這個總權重不會變
}
//這塊是快取資料的，大家細看下，不囉嗦了
if (!updateLock.get() && invokers.size() != map.size()) {
if (updateLock.compareAndSet(false, true)) {
try {
// copy -> modify -> update reference
ConcurrentMap<String, WeightedRoundRobin> newMap = new ConcurrentHashMap<String, WeightedRoundRobin>();
newMap.putAll(map);
Iterator<Entry<String, WeightedRoundRobin>> it = newMap.entrySet().iterator();
while (it.hasNext()) {
Entry<String, WeightedRoundRobin> item = it.next();
if (now - item.getValue().getLastUpdate() > RECYCLE_PERIOD) {
it.remove();
}
}
methodWeightMap.put(key, newMap);
} finally {
updateLock.set(false);
}
}
}
//這塊也很關鍵，每次選定服務提供者後，會把這個服務提供者的當前權重值減去總權重
if (selectedInvoker != null) {
selectedWRR.sel(totalWeight);
return selectedInvoker;
}
// should not happen here
return invokers.get(0);
}
}複製程式碼看程式碼還是不清晰？沒關係，下面我畫張圖來表述下，還看不懂，你來打我。
假設有三個服務提供者A，B，C,權重分別為1:3:5 （相同權重不講了，按列表順序從前往後迴圈就行了）。
下面附上我的測試程式碼，結果和上圖演示結果一致。
package loadbalance;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
/**
* @author <a href="mailto:wujia@2dfire.com">linxiaohui</a>
* @version 1.0 2018/12/17
* @since 1.0
*/
public class RoundRobinLoadBalance {
public static final String NAME = "roundrobin";
private static int RECYCLE_PERIOD = 60000;
protected static class WeightedRoundRobin {
private int weight;
private AtomicLong current = new AtomicLong(0);
private long lastUpdate;
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
current.set(0);
}
public long increaseCurrent() {
return current.addAndGet(weight);
}
public void sel(int total) {
current.addAndGet(-1 * total);
}
public long getLastUpdate() {
return lastUpdate;
}
public void setLastUpdate(long lastUpdate) {
this.lastUpdate = lastUpdate;
}
}
private ConcurrentMap<String, ConcurrentMap<String, WeightedRoundRobin>> methodWeightMap = new ConcurrentHashMap<String, ConcurrentMap<String, WeightedRoundRobin>>();
private AtomicBoolean updateLock = new AtomicBoolean();
public Invoker doSelect(List<Invoker> invokers) {
String key = invokers.get(0).getMethodKey();
ConcurrentMap<String, WeightedRoundRobin> map = methodWeightMap.get(key);
if (map == null) {
methodWeightMap.putIfAbsent(key, new ConcurrentHashMap<String, WeightedRoundRobin>());
map = methodWeightMap.get(key);
}
int totalWeight = 0;
long maxCurrent = Long.MIN_VALUE;
long now = System.currentTimeMillis();
Invoker selectedInvoker = null;
WeightedRoundRobin selectedWRR = null;
for (Invoker invoker : invokers) {
String identifyString = invoker.getUrlKey();
WeightedRoundRobin weightedRoundRobin = map.get(identifyString);
int weight = invoker.getWeight();
if (weight < 0) {
weight = 0;
}
if (weightedRoundRobin == null) {
weightedRoundRobin = new WeightedRoundRobin();
weightedRoundRobin.setWeight(weight);
map.putIfAbsent(identifyString, weightedRoundRobin);
weightedRoundRobin = map.get(identifyString);
}
if (weight != weightedRoundRobin.getWeight()) {
//weight changed
weightedRoundRobin.setWeight(weight);
}
long cur = weightedRoundRobin.increaseCurrent();
weightedRoundRobin.setLastUpdate(now);
if (cur > maxCurrent) {
maxCurrent = cur;
selectedInvoker = invoker;
selectedWRR = weightedRoundRobin;
}
totalWeight += weight;
}
if (!updateLock.get() && invokers.size() != map.size()) {
if (updateLock.compareAndSet(false, true)) {
try {
// copy -> modify -> update reference
ConcurrentMap<String, WeightedRoundRobin> newMap = new ConcurrentHashMap<String, WeightedRoundRobin>();
newMap.putAll(map);
Iterator<Map.Entry<String, WeightedRoundRobin>> it = newMap.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, WeightedRoundRobin> item = it.next();
if (now - item.getValue().getLastUpdate() > RECYCLE_PERIOD) {
it.remove();
}
}
methodWeightMap.put(key, newMap);
} finally {
updateLock.set(false);
}
}
}
if (selectedInvoker != null) {
selectedWRR.sel(totalWeight);
return selectedInvoker;
}
// should not happen here
return invokers.get(0);
}
public static void main(String[] args) {
List<Invoker> invokers = new LinkedList<>();
Invoker invoker = new Invoker("A", "dubbo://10.121.135.25:20880/DemoService/sayHello", "dubbo://10.121.135.25:20880/DemoService", 1);
Invoker invoker2 = new Invoker("B", "dubbo://10.121.135.26:20880/DemoService/sayHello", "dubbo://10.121.135.26:20880/DemoService", 3);
Invoker invoker3 = new Invoker("C", "dubbo://10.121.135.27:20880/DemoService/sayHello", "dubbo://10.121.135.27:20880/DemoService", 5);
invokers.add(invoker);
invokers.add(invoker2);
invokers.add(invoker3);
RoundRobinLoadBalance balance = new RoundRobinLoadBalance();
for (int i = 0; i < 10; i++) {
Invoker selectedInvoker = balance.doSelect(invokers);
System.out.println(selectedInvoker.getName() + " 方法權重:" + selectedInvoker.getWeight());
}
}
}複製程式碼附上我模擬的服務提供者
package loadbalance;
/**
* @author <a href="mailto:wujia@2dfire.com">linxiaohui</a>
* @version 1.0 2018/12/17
* @since 1.0
*/
public class Invoker {
private String methodKey;
private Integer weight;
private String urlKey;
private String name;
public Invoker(String name, String methodKey, String urlKey, Integer weight) {
this.name = name;
this.methodKey = methodKey;
this.urlKey = urlKey;
this.weight = weight;
}
public String getMethodKey() {
return methodKey;
}
public void setMethodKey(String methodKey) {
this.methodKey = methodKey;
}
public Integer getWeight() {
return weight;
}
public void setWeight(Integer weight) {
this.weight = weight;
}
public String getUrlKey() {
return urlKey;
}
public void setUrlKey(String urlKey) {
this.urlKey = urlKey;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}複製程式碼測試結果圖：
小結
目前網上的一些dubbo的原始碼分析文章都是基於比較舊的版本，最新版本的已經發生了變化。鑑於這個原因，我會在後續抽空把dubbo的一些原始碼閱讀逐步分享給大家。最近專案忙成狗?，先寫到這吧。