[GitHub] [pulsar] heesung-sn 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>]

heesung-sn commented on code in PR #14971:
URL: https://github.com/apache/pulsar/pull/14971#discussion_r897334149


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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:
   Afaik, this `brokerResourceUsage` is relatively short-term data(every 5 sec).  Can you share why we are using this short-term usage data in this `getScore()` function?
   
   For example, I am wondering how we are going to handle the following scenarios. 
   - In one sample, one broker was temporally idle, but afterward, it became mostly busy.
   - In one sample, conversely, one broker was temporally very busy, but afterward, it became mostly idle.
   
   I don't think there is a definitive answer here, but could you share why we only use the short-term usage data here?



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