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 */
018
019package org.apache.hadoop.hdfs.server.blockmanagement;
020
021import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY;
022import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT;
023
024import java.util.Random;
025
026import org.apache.commons.logging.Log;
027import org.apache.commons.logging.LogFactory;
028import org.apache.hadoop.conf.Configuration;
029import org.apache.hadoop.hdfs.DFSConfigKeys;
030import org.apache.hadoop.net.NetworkTopology;
031
032/**
033 * Space balanced block placement policy.
034 */
035public class AvailableSpaceBlockPlacementPolicy extends
036    BlockPlacementPolicyDefault {
037  private static final Log LOG = LogFactory
038      .getLog(AvailableSpaceBlockPlacementPolicy.class);
039  private static final Random RAND = new Random();
040  private int balancedPreference =
041      (int) (100 * DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT);
042
043  @Override
044  public void initialize(Configuration conf, FSClusterStats stats,
045      NetworkTopology clusterMap, Host2NodesMap host2datanodeMap) {
046    super.initialize(conf, stats, clusterMap, host2datanodeMap);
047    float balancedPreferencePercent =
048        conf.getFloat(
049          DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY,
050          DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT);
051
052    LOG.info("Available space block placement policy initialized: "
053        + DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY
054        + " = " + balancedPreferencePercent);
055
056    if (balancedPreferencePercent > 1.0) {
057      LOG.warn("The value of "
058          + DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY
059          + " is greater than 1.0 but should be in the range 0.0 - 1.0");
060    }
061    if (balancedPreferencePercent < 0.5) {
062      LOG.warn("The value of "
063          + DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY
064          + " is less than 0.5 so datanodes with more used percent will"
065          + " receive  more block allocations.");
066    }
067    balancedPreference = (int) (100 * balancedPreferencePercent);
068  }
069
070  @Override
071  protected DatanodeDescriptor chooseDataNode(String scope) {
072    DatanodeDescriptor a = (DatanodeDescriptor) clusterMap.chooseRandom(scope);
073    DatanodeDescriptor b = (DatanodeDescriptor) clusterMap.chooseRandom(scope);
074    if (a != null && b != null){
075      int ret = compareDataNode(a, b);
076      if (ret == 0) {
077        return a;
078      } else if (ret < 0) {
079        return (RAND.nextInt(100) < balancedPreference) ? a : b;
080      } else {
081        return (RAND.nextInt(100) < balancedPreference) ? b : a;
082      }
083    } else {
084      return a == null ? b : a;
085    }
086  }
087
088  /**
089   * Compare the two data nodes.
090   */
091  protected int compareDataNode(final DatanodeDescriptor a,
092      final DatanodeDescriptor b) {
093    if (a.equals(b)
094        || Math.abs(a.getDfsUsedPercent() - b.getDfsUsedPercent()) < 5) {
095      return 0;
096    }
097    return a.getDfsUsedPercent() < b.getDfsUsedPercent() ? -1 : 1;
098  }
099}