001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.master.balancer;
019
020import static org.apache.hadoop.hbase.master.balancer.DistributeReplicasConditional.getReplicaKey;
021
022import java.util.ArrayList;
023import java.util.HashSet;
024import java.util.List;
025import java.util.Set;
026import org.apache.hadoop.hbase.master.balancer.replicas.ReplicaKey;
027import org.apache.yetus.audience.InterfaceAudience;
028import org.slf4j.Logger;
029import org.slf4j.LoggerFactory;
030
031/**
032 * CandidateGenerator to distribute colocated replicas across different servers.
033 */
034@InterfaceAudience.Private
035final class DistributeReplicasCandidateGenerator extends RegionPlanConditionalCandidateGenerator {
036
037  private static final Logger LOG =
038    LoggerFactory.getLogger(DistributeReplicasCandidateGenerator.class);
039  private static final int BATCH_SIZE = 100_000;
040
041  DistributeReplicasCandidateGenerator(BalancerConditionals balancerConditionals) {
042    super(balancerConditionals);
043  }
044
045  @Override
046  BalanceAction generateCandidate(BalancerClusterState cluster, boolean isWeighing) {
047    return generateCandidate(cluster, isWeighing, false);
048  }
049
050  BalanceAction generateCandidate(BalancerClusterState cluster, boolean isWeighing,
051    boolean isForced) {
052    if (cluster.getMaxReplicas() < cluster.numRacks) {
053      LOG.trace("Skipping replica distribution as there are not enough racks to distribute them.");
054      return BalanceAction.NULL_ACTION;
055    }
056
057    // Iterate through shuffled servers to find colocated replicas
058    boolean foundColocatedReplicas = false;
059    List<MoveRegionAction> moveRegionActions = new ArrayList<>();
060    List<Integer> shuffledServerIndices = cluster.getShuffledServerIndices();
061    for (int sourceIndex : shuffledServerIndices) {
062      if (moveRegionActions.size() >= BATCH_SIZE || cluster.isStopRequested()) {
063        break;
064      }
065      int[] serverRegions = cluster.regionsPerServer[sourceIndex];
066      Set<ReplicaKey> replicaKeys = new HashSet<>(serverRegions.length);
067      for (int regionIndex : serverRegions) {
068        ReplicaKey replicaKey = getReplicaKey(cluster.regions[regionIndex]);
069        if (replicaKeys.contains(replicaKey)) {
070          foundColocatedReplicas = true;
071          if (isWeighing) {
072            // If weighing, fast exit with an actionable move
073            return getAction(sourceIndex, regionIndex, pickOtherRandomServer(cluster, sourceIndex),
074              -1);
075          }
076          // If not weighing, pick a good move
077          for (int i = 0; i < cluster.numServers; i++) {
078            // Randomize destination ordering so we aren't overloading one destination
079            int destinationIndex = pickOtherRandomServer(cluster, sourceIndex);
080            if (destinationIndex == sourceIndex) {
081              continue;
082            }
083            MoveRegionAction possibleAction =
084              new MoveRegionAction(regionIndex, sourceIndex, destinationIndex);
085            if (isForced) {
086              return possibleAction;
087            }
088            if (willBeAccepted(cluster, possibleAction)) {
089              cluster.doAction(possibleAction); // Update cluster state to reflect move
090              moveRegionActions.add(possibleAction);
091              break;
092            }
093          }
094        } else {
095          replicaKeys.add(replicaKey);
096        }
097      }
098    }
099
100    if (!moveRegionActions.isEmpty()) {
101      return batchMovesAndResetClusterState(cluster, moveRegionActions);
102    }
103    // If no colocated replicas are found, return NULL_ACTION
104    if (foundColocatedReplicas) {
105      LOG.warn("Could not find a place to put a colocated replica! We will force a move.");
106      return generateCandidate(cluster, isWeighing, true);
107    }
108    LOG.trace("No colocated replicas found. No balancing action required.");
109    return BalanceAction.NULL_ACTION;
110  }
111}