[GitHub] [helix] jiajunwang commented on a change in pull request #1935: Implement java API and utils for virtual topology group

[GitBox <gi...@apache.org>]

jiajunwang commented on a change in pull request #1935:
URL: https://github.com/apache/helix/pull/1935#discussion_r788057091



##########
File path: helix-core/src/main/java/org/apache/helix/cloud/topology/VirtualTopologyGroupStrategy.java
##########
@@ -0,0 +1,80 @@
+package org.apache.helix.cloud.topology;
+
+/*
+ * 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 com.google.common.collect.ImmutableMap;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import org.apache.helix.util.HelixUtil;
+
+public enum VirtualTopologyGroupStrategy {
+
+  /**
+   * A default assignment strategy that is deterministic and stable where:
+   * 1. assignment is guaranteed consistent for same inputs.
+   * 2. number of instance shuffles is reduced.
+   */
+  DEFAULT {
+    @Override
+    public Map<String, Set<String>> computeAssignment(
+        int numGroups, String virtualGroupName, Map<String, Set<String>> zoneMapping) {
+      List<String> sortedInstances = HelixUtil.sortAndFlattenZoneMapping(zoneMapping);
+      Map<String, Set<String>> assignment = new HashMap<>();
+      int instancesPerGroup = sortedInstances.size() / numGroups;
+
+      // instances.size = instancePerGroup * numGroups + residual
+      // step 1, continuously assign following groupInd order until entering residual section
+      for (int instanceInd = 0; instanceInd < instancesPerGroup * numGroups; instanceInd++) {
+        int groupIndex = instanceInd / instancesPerGroup;
+        String groupId = computeVirtualGroupId(groupIndex, virtualGroupName);
+        assignment.putIfAbsent(groupId, new HashSet<>());
+        assignment.get(groupId).add(sortedInstances.get(instanceInd));
+      }
+      // step 2, assign the residuals, either stick to the last assigned group or round-robin to all groups.
+      for (int instanceInd = instancesPerGroup * numGroups; instanceInd < sortedInstances.size(); instanceInd++) {
+        int groupIndex = numGroups <= zoneMapping.keySet().size()
+            ? numGroups - 1
+            : instanceInd % numGroups;
+        String groupId = computeVirtualGroupId(groupIndex, virtualGroupName);
+        assignment.putIfAbsent(groupId, new HashSet<>());
+        assignment.get(groupId).add(sortedInstances.get(instanceInd));
+      }
+      return ImmutableMap.copyOf(assignment);
+    }
+  };
+
+  /**
+   * Compute the assignment for each virtual topology group.
+   *
+   * @param numGroups number of the virtual groups
+   * @param virtualGroupName virtual group name
+   * @param zoneMapping current zone mapping from zoneId to instanceIds
+   * @return the assignment as mapping from virtual group ID to instanceIds
+   */
+  public abstract Map<String, Set<String>> computeAssignment(
+      int numGroups, String virtualGroupName, Map<String, Set<String>> zoneMapping);
+
+  private static String computeVirtualGroupId(int groupIndex, String virtualGroupName) {
+    return virtualGroupName + "_" + groupIndex;

Review comment:
       nit, avoid hard code?




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