[GitHub] [pulsar] dragonls commented on a diff in pull request #14971: [feature][broker] Add new load manager strategy for load manager to select broker having load below average.

[GitBox <gi...@apache.org>]

dragonls commented on code in PR #14971:
URL: https://github.com/apache/pulsar/pull/14971#discussion_r897934631


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pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/ThresholdLoadManagerStrategy.java:
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@@ -0,0 +1,131 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.loadbalance.impl;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.pulsar.broker.ServiceConfiguration;
+import org.apache.pulsar.broker.loadbalance.LoadData;
+import org.apache.pulsar.broker.loadbalance.ModularLoadManagerStrategy;
+import org.apache.pulsar.policies.data.loadbalancer.BrokerData;
+import org.apache.pulsar.policies.data.loadbalancer.BundleData;
+import org.apache.pulsar.policies.data.loadbalancer.LocalBrokerData;
+
+/**
+ * Placement strategy which randomly selects a broker from those having resource usage below average load.
+ */
+@Slf4j
+public class ThresholdLoadManagerStrategy implements ModularLoadManagerStrategy {
+    // Maintain this list to reduce object creation.
+    private final ArrayList<String> bestBrokers;
+
+    // candidate broker -> broker usage.
+    private final Map<String, Double> brokerUsages;
+
+    public ThresholdLoadManagerStrategy() {
+        bestBrokers = new ArrayList<>();
+        brokerUsages = new HashMap<>();
+    }
+
+    private static double getScore(final BrokerData brokerData, final ServiceConfiguration conf) {
+        final double overloadThreshold = conf.getLoadBalancerBrokerOverloadedThresholdPercentage() / 100.0;
+        final double maxUsage = brokerData.getLocalData().getMaxResourceUsage();
+        if (maxUsage > overloadThreshold) {
+            log.warn("Broker {} is overloaded: max usage={}", brokerData.getLocalData().getWebServiceUrl(), maxUsage);
+            return Double.POSITIVE_INFINITY;
+        }
+
+        double brokerResourceUsage = brokerData.getLocalData().getMaxResourceUsageWithWeight(

Review Comment:
   You are right. `brokerResourceUsage` is relatively short-term data.
   
   As for your question, using short-term data is also ok. Because the strategy here only affect scenarios where new traffic needs to be loaded. Once the broker is busy, it should not be selected for new traffic. Once the broker is idle, it is good to be selected for new traffic as well. Once more, there is random selection logic here to prevent a lot of traffic from being loaded on a single broker.



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