[GitHub] [kafka] cmccabe commented on a change in pull request #10494: KAFKA-12788: improve KRaft replica placement

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cmccabe commented on a change in pull request #10494:
URL: https://github.com/apache/kafka/pull/10494#discussion_r632769701



##########
File path: metadata/src/test/java/org/apache/kafka/controller/StripedReplicaPlacerTest.java
##########
@@ -0,0 +1,182 @@
+/*
+ * 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.kafka.controller;
+
+import org.apache.kafka.common.errors.InvalidReplicationFactorException;
+import org.apache.kafka.controller.StripedReplicaPlacer.BrokerList;
+import org.apache.kafka.controller.StripedReplicaPlacer.RackList;
+import org.apache.kafka.metadata.UsableBroker;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Timeout;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+
+@Timeout(value = 40)
+public class StripedReplicaPlacerTest {
+    /**
+     * Test that the BrokerList class works as expected.
+     */
+    @Test
+    public void testBrokerList() {
+        assertEquals(0, BrokerList.EMPTY.size());
+        assertEquals(-1, BrokerList.EMPTY.next(1));
+        BrokerList brokers = new BrokerList().add(0).add(1).add(2).add(3);
+        assertEquals(4, brokers.size());
+        assertEquals(0, brokers.next(0));
+        assertEquals(1, brokers.next(0));
+        assertEquals(2, brokers.next(0));
+        assertEquals(3, brokers.next(0));
+        assertEquals(-1, brokers.next(0));
+        assertEquals(-1, brokers.next(0));
+        assertEquals(1, brokers.next(1));
+        assertEquals(2, brokers.next(1));
+        assertEquals(3, brokers.next(1));
+        assertEquals(0, brokers.next(1));
+        assertEquals(-1, brokers.next(1));
+    }
+
+    /**
+     * Test that we perform striped replica placement as expected, and don't use the
+     * fenced replica if we don't have to.
+     */
+    @Test
+    public void testAvoidFencedReplicaIfPossibleOnSingleRack() {
+        MockRandom random = new MockRandom();
+        RackList rackList = new RackList(random, Arrays.asList(
+            new UsableBroker(3, Optional.empty(), false),
+            new UsableBroker(1, Optional.empty(), true),
+            new UsableBroker(0, Optional.empty(), false),
+            new UsableBroker(4, Optional.empty(), false),
+            new UsableBroker(2, Optional.empty(), false)).iterator());
+        assertEquals(5, rackList.numTotalBrokers());
+        assertEquals(4, rackList.numUnfencedBrokers());
+        assertEquals(Collections.singletonList(Optional.empty()), rackList.rackNames());
+        assertThrows(InvalidReplicationFactorException.class, () -> rackList.place(0));
+        assertThrows(InvalidReplicationFactorException.class, () -> rackList.place(-1));
+        assertEquals(Arrays.asList(3, 4, 0, 2), rackList.place(4));
+        assertEquals(Arrays.asList(4, 0, 2, 3), rackList.place(4));
+        assertEquals(Arrays.asList(0, 2, 3, 4), rackList.place(4));
+        assertEquals(Arrays.asList(2, 3, 4, 0), rackList.place(4));
+        assertEquals(Arrays.asList(0, 4, 3, 2), rackList.place(4));
+    }
+
+    /**
+     * Test that we will place on the fenced replica if we need to.
+     */
+    @Test
+    public void testPlacementOnFencedReplicaOnSingleRack() {
+        MockRandom random = new MockRandom();
+        RackList rackList = new RackList(random, Arrays.asList(
+            new UsableBroker(3, Optional.empty(), false),
+            new UsableBroker(1, Optional.empty(), true),
+            new UsableBroker(2, Optional.empty(), false)).iterator());
+        assertEquals(3, rackList.numTotalBrokers());
+        assertEquals(2, rackList.numUnfencedBrokers());
+        assertEquals(Collections.singletonList(Optional.empty()), rackList.rackNames());
+        assertEquals(Arrays.asList(3, 2, 1), rackList.place(3));
+        assertEquals(Arrays.asList(2, 3, 1), rackList.place(3));
+        assertEquals(Arrays.asList(3, 2, 1), rackList.place(3));

Review comment:
       Because broker 1 is fenced, we don't place a replica there until we need to (there are no more replicas remaining).  So it will always be the last / least preferred replica if we have 3 brokers and need a partition with replication factor 3




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