[GitHub] [kafka] Hangleton commented on a diff in pull request #13443: KAFKA-14514: Add Server Side Sticky Range Assignor (KIP-848)

["Hangleton (via GitHub)" <gi...@apache.org>]

Hangleton commented on code in PR #13443:
URL: https://github.com/apache/kafka/pull/13443#discussion_r1157238218


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group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/ServerSideStickyRangeAssignor.java:
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@@ -0,0 +1,268 @@
+/*
+ * 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.
+ */
+
+/**
+ * <p>The Server Side Sticky Range Assignor inherits properties of both the range assignor and the sticky assignor.
+ * Properties are :-
+ * <ul>
+ * <li> 1) Each consumer must get at least one partition per topic that it is subscribed to whenever the number of consumers is
+ *    less than or equal to the number of partitions for that topic. (Range) </li>
+ * <li> 2) Partitions should be assigned to consumers in a way that facilitates join operations where required. (Range) </li>
+ *    This can only be done if the topics are co-partitioned in the first place
+ *    Co-partitioned:-
+ *    Two streams are co-partitioned if the following conditions are met:-
+ * ->The keys must have the same schemas
+ * ->The topics involved must have the same number of partitions
+ * <li> 3) Consumers should retain as much as their previous assignment as possible. (Sticky) </li>
+ * </ul>
+ * </p>
+ *
+ * <p>The algorithm works mainly in 5 steps described below
+ * <ul>
+ * <li> 1) Get a map of the consumersPerTopic created using the member subscriptions.</li>
+ * <li> 2) Get a list of consumers (potentiallyUnfilled) that have not met the minimum required quota for assignment AND
+ * get a list of sticky partitions that we want to retain in the new assignment.</li>
+ * <li> 3) Add consumers from potentiallyUnfilled to Unfilled if they haven't met the total required quota = minQuota + (if necessary) extraPartition </li>
+ * <li> 4) Get a list of available partitions by calculating the difference between total partitions and assigned sticky partitions </li>
+ * <li> 5) Iterate through unfilled consumers and assign partitions from available partitions </li>
+ * </ul>
+ * </p>
+ *
+ */
+package org.apache.kafka.coordinator.group.assignor;
+
+
+import org.apache.kafka.common.Uuid;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.HashMap;
+import java.util.Collections;
+
+import static java.lang.Math.min;
+
+public class ServerSideStickyRangeAssignor implements PartitionAssignor {
+
+    public static final String RANGE_ASSIGNOR_NAME = "range-sticky";
+
+    @Override
+    public String name() {
+        return RANGE_ASSIGNOR_NAME;
+    }
+
+    protected static <K, V> void putList(Map<K, List<V>> map, K key, V value) {
+        List<V> list = map.computeIfAbsent(key, k -> new ArrayList<>());
+        list.add(value);
+    }
+
+    protected static <K, V> void putSet(Map<K, Set<V>> map, K key, V value) {
+        Set<V> set = map.computeIfAbsent(key, k -> new HashSet<>());
+        set.add(value);
+    }
+
+    static class Pair<T, U> {
+        private final T first;
+        private final U second;
+
+        public Pair(T first, U second) {
+            this.first = first;
+            this.second = second;
+        }
+
+        public T getFirst() {
+            return first;
+        }
+
+        public U getSecond() {
+            return second;
+        }
+
+        @Override
+        public String toString() {
+            return "(" + first + ", " + second + ")";
+        }
+    }
+
+    // Returns a map of the list of consumers per Topic (keyed by topicId)
+    private Map<Uuid, List<String>> consumersPerTopic(AssignmentSpec assignmentSpec) {

Review Comment:
   Are you referring to adding the `final` modifier to the parameter `assignmentSpec` or the method `consumersPerTopic`?



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