[GitHub] [incubator-pinot] snleee commented on a change in pull request #4269: Add interface and implementations for the new segment assignment

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snleee commented on a change in pull request #4269: Add interface and implementations for the new segment assignment
URL: https://github.com/apache/incubator-pinot/pull/4269#discussion_r290086469
 
 

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 File path: pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/RealtimeSegmentAssignmentStrategy.java
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+/**
+ * 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.pinot.controller.helix.core.assignment.segment;
+
+import com.google.common.base.Preconditions;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.helix.ZNRecord;
+import org.apache.helix.store.zk.ZkHelixPropertyStore;
+import org.apache.pinot.common.config.TableConfig;
+import org.apache.pinot.common.utils.LLCSegmentName;
+import org.apache.pinot.controller.helix.core.assignment.InstancePartitions;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Segment assignment strategy for LLC real-time segments.
+ * <p>It is very similar to replica-group based segment assignment with the following differences:
+ * <ul>
+ *   <li>1. Each partition always contains one server</li>
+ *   <li>2. In addition to the ONLINE segments, there are also CONSUMING segments to be assigned</li>
+ * </ul>
+ * <p>
+ *   Since each partition contains only one server (in one replica), we can directly assign or rebalance segments to the
+ *   servers based on the partition id.
+ * <p>
+ *   The real-time segment assignment does not minimize segment moves because the server is fixed for each partition in
+ *   each replica. The instance assignment is responsible for keeping minimum changes to the instance partitions to
+ *   reduce the number of segments need to be moved.
+ */
+public class RealtimeSegmentAssignmentStrategy implements SegmentAssignmentStrategy {
+  private static final Logger LOGGER = LoggerFactory.getLogger(RealtimeSegmentAssignmentStrategy.class);
+
+  private String _tableNameWithType;
+  private int _replication;
+
+  @Override
+  public void init(ZkHelixPropertyStore<ZNRecord> propertyStore, TableConfig tableConfig) {
+    _tableNameWithType = tableConfig.getTableName();
+    _replication = tableConfig.getValidationConfig().getReplicasPerPartitionNumber();
+
+    LOGGER.info("Initialized RealtimeSegmentAssignmentStrategy for table: {} with replication: {}", _tableNameWithType,
+        _replication);
+  }
+
+  @Override
+  public List<String> assignSegment(String segmentName, Map<String, Map<String, String>> currentAssignment,
+      InstancePartitions instancePartitions) {
+    Preconditions.checkState(instancePartitions.getNumPartitions() == 1,
+        "The instance partitions should contain only 1 partition");
+
+    int numReplicas = getNumReplicas(instancePartitions);
+    int partitionId = new LLCSegmentName(segmentName).getPartitionId();
+    List<String> instancesAssigned = new ArrayList<>(numReplicas);
+    for (int replicaId = 0; replicaId < numReplicas; replicaId++) {
+      instancesAssigned.add(getInstance(instancePartitions, partitionId, replicaId));
+    }
+    LOGGER.info("Assigned segment: {} with partition id: {} to instances: {} for table: {}", segmentName, partitionId,
+        instancesAssigned, _tableNameWithType);
+    return instancesAssigned;
+  }
+
+  @Override
+  public Map<String, Map<String, String>> rebalanceTable(Map<String, Map<String, String>> currentAssignment,
+      InstancePartitions instancePartitions) {
+    Preconditions.checkState(instancePartitions.getNumPartitions() == 1,
+        "The instance partitions should contain only 1 partition");
+
+    int numReplicas = getNumReplicas(instancePartitions);
+    Map<String, Map<String, String>> newAssignment = new TreeMap<>();
+    for (Map.Entry<String, Map<String, String>> entry : currentAssignment.entrySet()) {
+      String segmentName = entry.getKey();
+      int partitionId = new LLCSegmentName(segmentName).getPartitionId();
+      String state = entry.getValue().values().iterator().next();
+      newAssignment.put(segmentName, getInstanceStateMap(instancePartitions, partitionId, numReplicas, state));
+    }
+
+    LOGGER.info(
+        "Rebalanced {} segments with {} replicas and instance partitions: {} for table: {}, number of segments to be moved to each instance: {}",
+        currentAssignment.size(), numReplicas, instancePartitions, _tableNameWithType,
+        SegmentAssignmentUtils.getNumSegmentsToBeMoved(currentAssignment, newAssignment));
+    return newAssignment;
+  }
+
+  private int getNumReplicas(InstancePartitions instancePartitions) {
+    int numReplicas = instancePartitions.getNumReplicas();
+    if (numReplicas == 1) {
 
 Review comment:
   This code is relevant to the above comment on variable name

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