Add soft constraint: ResourcePartitionAntiAffinityConstraint (#464)

If the resource of the partition overall has a light load on the instance, the score is higher compared to case when the resource is heavily loaded on the instance

helix-core/src/main/java/org/apache/helix/controller/rebalancer/waged/constraints/ResourcePartitionAntiAffinityConstraint.java

@@ -0,0 +1,52 @@
+package org.apache.helix.controller.rebalancer.waged.constraints;
+
+/*
+ * 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.
+ */
+
+import org.apache.helix.controller.rebalancer.waged.model.AssignableNode;
+import org.apache.helix.controller.rebalancer.waged.model.AssignableReplica;
+import org.apache.helix.controller.rebalancer.waged.model.ClusterContext;
+
+/**
+ * This constraint exists to make partitions belonging to the same resource be assigned as far from
+ * each other as possible. This is because it is undesirable to have many partitions belonging to
+ * the same resource be assigned to the same node to minimize the impact of node failure scenarios.
+ * The score is higher the fewer the partitions are on the node belonging to the same resource.
+ */
+class ResourcePartitionAntiAffinityConstraint extends SoftConstraint {
+  private static final float MAX_SCORE = 1f;
+  private static final float MIN_SCORE = 0f;
+
+  ResourcePartitionAntiAffinityConstraint() {
+    super(MAX_SCORE, MIN_SCORE);
+  }
+
+  @Override
+  protected float getAssignmentScore(AssignableNode node, AssignableReplica replica,
+      ClusterContext clusterContext) {
+    String resource = replica.getResourceName();
+    int curPartitionCountForResource = node.getAssignedPartitionsByResource(resource).size();
+    int doubleMaxPartitionCountForResource =
+        2 * clusterContext.getEstimatedMaxPartitionByResource(resource);
+    // The score measures the twice the max allowed count versus current counts
+    // The returned value is a measurement of remaining quota ratio, in the case of exceeding allowed counts, return 0
+    return Math.max(((float) doubleMaxPartitionCountForResource - curPartitionCountForResource)
+        / doubleMaxPartitionCountForResource, 0);
+  }
+}

helix-core/src/test/java/org/apache/helix/controller/rebalancer/waged/constraints/TestResourcePartitionAntiAffinityConstraint.java

@@ -0,0 +1,67 @@
+package org.apache.helix.controller.rebalancer.waged.constraints;
+
+/*
+ * 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.
+ */
+
+import static org.mockito.Mockito.when;
+
+import java.util.Collections;
+
+import org.apache.helix.controller.rebalancer.waged.model.AssignableNode;
+import org.apache.helix.controller.rebalancer.waged.model.AssignableReplica;
+import org.apache.helix.controller.rebalancer.waged.model.ClusterContext;
+import org.mockito.Mockito;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+import com.google.common.collect.ImmutableSet;
+
+public class TestResourcePartitionAntiAffinityConstraint {
+  private static final String TEST_PARTITION = "TestPartition";
+  private static final String TEST_RESOURCE = "TestResource";
+  private final AssignableReplica _testReplica = Mockito.mock(AssignableReplica.class);
+  private final AssignableNode _testNode = Mockito.mock(AssignableNode.class);
+  private final ClusterContext _clusterContext = Mockito.mock(ClusterContext.class);
+  private final SoftConstraint _constraint = new ResourcePartitionAntiAffinityConstraint();
+
+  @Test
+  public void testGetAssignmentScore() {
+    when(_testReplica.getResourceName()).thenReturn(TEST_RESOURCE);
+    when(_testNode.getAssignedPartitionsByResource(TEST_RESOURCE)).thenReturn(
+        ImmutableSet.of(TEST_PARTITION + "1", TEST_PARTITION + "2", TEST_PARTITION + "3"));
+    when(_clusterContext.getEstimatedMaxPartitionByResource(TEST_RESOURCE)).thenReturn(10);
+
+    float score = _constraint.getAssignmentScore(_testNode, _testReplica, _clusterContext);
+    float normalizedScore = _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
+    Assert.assertEquals(score, 0.85f);
+    Assert.assertEquals(normalizedScore, 0.85f);
+  }
+
+  @Test
+  public void testGetAssignmentScoreMaxScore() {
+    when(_testReplica.getResourceName()).thenReturn(TEST_RESOURCE);
+    when(_testNode.getAssignedPartitionsByResource(TEST_RESOURCE)).thenReturn(Collections.emptySet());
+    when(_clusterContext.getEstimatedMaxPartitionByResource(TEST_RESOURCE)).thenReturn(10);
+
+    float score = _constraint.getAssignmentScore(_testNode, _testReplica, _clusterContext);
+    float normalizedScore = _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
+    Assert.assertEquals(score, 1f);
+    Assert.assertEquals(normalizedScore, 1f);
+  }
+}