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 java.util.ArrayList;
021import java.util.HashSet;
022import java.util.List;
023import java.util.Set;
024import org.apache.hadoop.hbase.ServerName;
025import org.apache.yetus.audience.InterfaceAudience;
026import org.slf4j.Logger;
027import org.slf4j.LoggerFactory;
028
029/**
030 * A simple candidate generator that attempts to move regions from the most-loaded servers to the
031 * least-loaded servers.
032 */
033@InterfaceAudience.Private
034final class SlopFixingCandidateGenerator extends RegionPlanConditionalCandidateGenerator {
035
036  private static final Logger LOG = LoggerFactory.getLogger(SlopFixingCandidateGenerator.class);
037
038  private final float slop;
039
040  SlopFixingCandidateGenerator(BalancerConditionals balancerConditionals) {
041    super(balancerConditionals);
042    this.slop = balancerConditionals.getConf().getFloat(BaseLoadBalancer.REGIONS_SLOP_KEY,
043      BaseLoadBalancer.REGIONS_SLOP_DEFAULT);
044  }
045
046  @Override
047  BalanceAction generateCandidate(BalancerClusterState cluster, boolean isWeighing) {
048    boolean isTableIsolationEnabled = getBalancerConditionals().isTableIsolationEnabled();
049    ClusterLoadState cs = new ClusterLoadState(cluster.clusterState);
050    float average = cs.getLoadAverage();
051    int ceiling = (int) Math.ceil(average * (1 + slop));
052    Set<Integer> sloppyServerIndices = new HashSet<>();
053    for (int i = 0; i < cluster.numServers; i++) {
054      int regionCount = cluster.regionsPerServer[i].length;
055      if (regionCount > ceiling) {
056        sloppyServerIndices.add(i);
057      }
058    }
059
060    if (sloppyServerIndices.isEmpty()) {
061      LOG.trace("No action to take because no sloppy servers exist.");
062      return BalanceAction.NULL_ACTION;
063    }
064
065    List<MoveRegionAction> moves = new ArrayList<>();
066    Set<ServerAndLoad> fixedServers = new HashSet<>();
067    for (int sourceServer : sloppyServerIndices) {
068      if (
069        isTableIsolationEnabled
070          && getBalancerConditionals().isServerHostingIsolatedTables(cluster, sourceServer)
071      ) {
072        // Don't fix sloppiness of servers hosting isolated tables
073        continue;
074      }
075      for (int regionIdx : cluster.regionsPerServer[sourceServer]) {
076        boolean regionFoundMove = false;
077        for (ServerAndLoad serverAndLoad : cs.getServersByLoad().keySet()) {
078          ServerName destinationServer = serverAndLoad.getServerName();
079          int destinationServerIdx = cluster.serversToIndex.get(destinationServer.getAddress());
080          int regionsOnDestination = cluster.regionsPerServer[destinationServerIdx].length;
081          if (regionsOnDestination < average) {
082            MoveRegionAction move =
083              new MoveRegionAction(regionIdx, sourceServer, destinationServerIdx);
084            if (willBeAccepted(cluster, move)) {
085              if (isWeighing) {
086                // Fast exit for weighing candidate
087                return move;
088              }
089              moves.add(move);
090              cluster.doAction(move);
091              regionFoundMove = true;
092              break;
093            }
094          } else {
095            fixedServers.add(serverAndLoad);
096          }
097        }
098        fixedServers.forEach(s -> cs.getServersByLoad().remove(s));
099        fixedServers.clear();
100        if (!regionFoundMove && LOG.isTraceEnabled()) {
101          LOG.trace("Could not find a destination for region {} from server {}.", regionIdx,
102            sourceServer);
103        }
104        if (cluster.regionsPerServer[sourceServer].length <= ceiling) {
105          break;
106        }
107      }
108    }
109
110    return batchMovesAndResetClusterState(cluster, moves);
111  }
112}