Jackie-Jiang 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_r292716220
########## File path: pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/SegmentAssignmentUtils.java ########## @@ -0,0 +1,274 @@ +/** + * 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.HashMap; +import java.util.LinkedHashMap; +import java.util.List; +import java.util.Map; +import java.util.PriorityQueue; +import java.util.Set; +import java.util.TreeMap; +import org.apache.helix.HelixManager; +import org.apache.helix.controller.rebalancer.strategy.AutoRebalanceStrategy; +import org.apache.pinot.common.config.TableConfig; +import org.apache.pinot.common.utils.CommonConstants.Helix.StateModel.RealtimeSegmentOnlineOfflineStateModel; +import org.apache.pinot.common.utils.CommonConstants.Helix.StateModel.SegmentOnlineOfflineStateModel; +import org.apache.pinot.common.utils.InstancePartitionsType; +import org.apache.pinot.common.utils.Pairs; +import org.apache.pinot.controller.helix.core.assignment.InstancePartitions; +import org.apache.pinot.controller.helix.core.assignment.InstancePartitionsUtils; + + +/** + * Utility class for segment assignment. + */ +class SegmentAssignmentUtils { + private SegmentAssignmentUtils() { + } + + /** + * Returns the number of segments assigned to each instance. + */ + static int[] getNumSegmentsAssigned(Map<String, Map<String, String>> segmentAssignment, List<String> instances) { + int[] numSegmentsPerInstance = new int[instances.size()]; + Map<String, Integer> instanceNameToIdMap = getInstanceNameToIdMap(instances); + for (Map<String, String> instanceStateMep : segmentAssignment.values()) { + for (String instanceName : instanceStateMep.keySet()) { + Integer instanceId = instanceNameToIdMap.get(instanceName); + if (instanceId != null) { + numSegmentsPerInstance[instanceId]++; + } + } + } + return numSegmentsPerInstance; + } + + private static Map<String, Integer> getInstanceNameToIdMap(List<String> instances) { + int numInstances = instances.size(); + Map<String, Integer> instanceNameToIdMap = new HashMap<>(); + for (int i = 0; i < numInstances; i++) { + instanceNameToIdMap.put(instances.get(i), i); + } + return instanceNameToIdMap; + } + + /** + * Returns the instances for the balance number segment assignment strategy. + */ + static List<String> getInstances(HelixManager helixManager, TableConfig tableConfig, int replication, + InstancePartitionsType instancePartitionsType) { + InstancePartitions instancePartitions = + InstancePartitionsUtils.fetchOrComputeInstancePartitions(helixManager, tableConfig, instancePartitionsType); + Preconditions.checkArgument(instancePartitions.getNumPartitions() == 1 && instancePartitions.getNumReplicas() == 1, + "The instance partitions: %s should contain only 1 partition and 1 replica", instancePartitions.getName()); + List<String> instances = instancePartitions.getInstances(0, 0); + Preconditions.checkState(instances.size() >= replication, + "There are less instances: %d than the replication: %d for table: %s", instances.size(), replication, + tableConfig.getTableName()); + return instances; + } + + /** + * Rebalances the table with Helix AutoRebalanceStrategy for the balance number segment assignment strategy. + */ + static Map<String, Map<String, String>> rebalanceTableWithHelixAutoRebalanceStrategy( + Map<String, Map<String, String>> currentAssignment, List<String> instances, int replication) { + // Use Helix AutoRebalanceStrategy to rebalance the table + LinkedHashMap<String, Integer> states = new LinkedHashMap<>(); + states.put(SegmentOnlineOfflineStateModel.ONLINE, replication); + AutoRebalanceStrategy autoRebalanceStrategy = + new AutoRebalanceStrategy(null, new ArrayList<>(currentAssignment.keySet()), states); + // Make a copy of the current assignment because this step might change the passed in assignment + Map<String, Map<String, String>> currentAssignmentCopy = new TreeMap<>(); + for (Map.Entry<String, Map<String, String>> entry : currentAssignment.entrySet()) { + String segmentName = entry.getKey(); + Map<String, String> instanceStateMap = entry.getValue(); + currentAssignmentCopy.put(segmentName, new TreeMap<>(instanceStateMap)); + } + return autoRebalanceStrategy.computePartitionAssignment(instances, instances, currentAssignmentCopy, null) + .getMapFields(); + } + + /** + * Rebalances the table for the replica-group based segment assignment strategy. + * <p>The number of partitions for the segments can be different from the number of partitions in the instance + * partitions. Uniformly spray the segment partitions over the instance partitions. + */ + static Map<String, Map<String, String>> rebalanceReplicaGroupBasedTable( + Map<String, Map<String, String>> currentAssignment, InstancePartitions instancePartitions, + Map<Integer, Set<String>> partitionIdToSegmentsMap) { + Map<String, Map<String, String>> newAssignment = new TreeMap<>(); + int numPartitions = instancePartitions.getNumPartitions(); + for (Map.Entry<Integer, Set<String>> entry : partitionIdToSegmentsMap.entrySet()) { + // Uniformly spray the segment partitions over the instance partitions + int partitionId = entry.getKey() % numPartitions; + SegmentAssignmentUtils + .rebalanceReplicaGroupBasedPartition(currentAssignment, instancePartitions, partitionId, entry.getValue(), + newAssignment); + } + return newAssignment; + } + + /** + * Rebalances one partition of the table for the replica-group based segment assignment strategy. + * <ul> + * <li> + * 1. Calculate the target number of segments on each server + * </li> + * <li> + * 2. Loop over all the segments and keep the assignment if target number of segments for the server has not been + * reached and track the not assigned segments + * </li> + * <li> + * 3. Assign the left-over segments to the servers with the least segments, or the smallest index if there is a + * tie + * </li> + * <li> + * 4. Mirror the assignment to other replicas + * </li> + * </ul> + */ + static void rebalanceReplicaGroupBasedPartition(Map<String, Map<String, String>> currentAssignment, + InstancePartitions instancePartitions, int partitionId, Set<String> segments, + Map<String, Map<String, String>> newAssignment) { + // Fetch instances in replica 0 + List<String> instances = instancePartitions.getInstances(partitionId, 0); + Map<String, Integer> instanceNameToIdMap = SegmentAssignmentUtils.getInstanceNameToIdMap(instances); + + // Calculate target number of segments per instance + int numInstances = instances.size(); + int numSegments = segments.size(); + int targetNumSegmentsPerInstance = (numSegments + numInstances - 1) / numInstances; Review comment: This is equivalent to Math.ceil() for integer. E.g. for 7 segments, 3 servers, we will target 3 segments per server. 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