Implement MaxCapacityUsageInstanceConstraint soft constraint (#463)

The constraint evaluates the score by checking the max used capacity key out of all the capacity
keys.
The higher the maximum usage value for the capacity key, the lower the score will be, implying
that it is that much less desirable to assign anything on the given node.
It is a greedy approach since it evaluates only the most used capacity key.

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

@@ -27,6 +27,7 @@
  * Evaluate by instance's current partition count versus estimated max partition count
  * Intuitively, Encourage the assignment if the instance's occupancy rate is below average;
  * Discourage the assignment if the instance's occupancy rate is above average
+ * The normalized score will be within [0, 1]
  */
 class InstancePartitionsCountConstraint extends SoftConstraint {
   private static final float MAX_SCORE = 1f;

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

@@ -0,0 +1,47 @@
+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;
+
+/**
+ * The constraint evaluates the score by checking the max used capacity key out of all the capacity
+ * keys.
+ * The higher the maximum usage value for the capacity key, the lower the score will be, implying
+ * that it is that much less desirable to assign anything on the given node.
+ * It is a greedy approach since it evaluates only on the most used capacity key.
+ */
+class MaxCapacityUsageInstanceConstraint extends SoftConstraint {
+  private static final float MIN_SCORE = 0;
+  private static final float MAX_SCORE = 1;
+
+  MaxCapacityUsageInstanceConstraint() {
+    super(MAX_SCORE, MIN_SCORE);
+  }
+
+  @Override
+  protected float getAssignmentScore(AssignableNode node, AssignableReplica replica,
+      ClusterContext clusterContext) {
+    float maxCapacityUsage = node.getHighestCapacityUtilization();
+    return 1.0f - maxCapacityUsage / 2.0f;
+  }
+}

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

@@ -24,7 +24,8 @@
 import org.apache.helix.controller.rebalancer.waged.model.ClusterContext;
 
 /**
- * The "soft" constraint evaluates the optimality of an assignment by giving it a score of a scale of [minScore, maxScore]
+ * The "soft" constraint evaluates the optimality of an assignment by giving it a score of a scale
+ * of [minScore, maxScore]
  * The higher the score, the better the assignment; Intuitively, the assignment is encouraged.
  * The lower score the score, the worse the assignment; Intuitively, the assignment is penalized.
  */

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

@@ -35,7 +35,7 @@ class SoftConstraintWeightModel {
   }
 
   static {
-    //TODO update the weight
+    // TODO update the weight
     MODEL = ImmutableMap.<Class, Float> builder().put(InstancePartitionsCountConstraint.class, 1.0f)
         .build();
   }

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

@@ -38,23 +38,26 @@ public class TestInstancePartitionsCountConstraint {
   @Test
   public void testWhenInstanceIsIdle() {
     when(_testNode.getAssignedReplicaCount()).thenReturn(0);
-    float score = _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
+    float score =
+        _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
     Assert.assertEquals(score, 1.0f);
   }
 
   @Test
   public void testWhenInstanceIsFull() {
     when(_testNode.getAssignedReplicaCount()).thenReturn(10);
     when(_clusterContext.getEstimatedMaxPartitionCount()).thenReturn(10);
-    float score = _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
+    float score =
+        _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
     Assert.assertEquals(score, 0.5f);
   }
 
   @Test
   public void testWhenInstanceHalfOccupied() {
     when(_testNode.getAssignedReplicaCount()).thenReturn(10);
     when(_clusterContext.getEstimatedMaxPartitionCount()).thenReturn(20);
-    float score = _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
+    float score =
+        _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
     Assert.assertEquals(score, 0.75f);
   }
 }

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

@@ -0,0 +1,56 @@
+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.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+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.testng.Assert;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.Test;
+
+public class TestMaxCapacityUsageInstanceConstraint {
+  private AssignableReplica _testReplica;
+  private AssignableNode _testNode;
+  private ClusterContext _clusterContext;
+  private final SoftConstraint _constraint = new MaxCapacityUsageInstanceConstraint();
+
+  @BeforeMethod
+  public void setUp() {
+    _testNode = mock(AssignableNode.class, CALLS_REAL_METHODS);
+    _testReplica = mock(AssignableReplica.class);
+    _clusterContext = mock(ClusterContext.class);
+  }
+
+  @Test
+  public void testGetNormalizedScore() {
+    when(_testNode.getHighestCapacityUtilization()).thenReturn(0.8f);
+    float score =
+            _constraint.getAssignmentScore(_testNode, _testReplica, _clusterContext);
+    Assert.assertEquals(score, 0.6f);
+    float normalizedScore =
+        _constraint.getAssignmentNormalizedScore(_testNode, _testReplica, _clusterContext);
+    Assert.assertEquals(normalizedScore, 0.6f);
+  }
+}