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.hdfs.server.datanode;
019
020import java.io.IOException;
021import java.util.List;
022
023import org.apache.hadoop.hdfs.server.datanode.FSDatasetInterface.FSVolumeInterface;
024import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
025
026public class RoundRobinVolumesPolicy implements BlockVolumeChoosingPolicy {
027
028  private int curVolume = 0;
029
030  @Override
031  public synchronized FSVolumeInterface chooseVolume(
032      List<FSVolumeInterface> volumes, long blockSize) throws IOException {
033    if(volumes.size() < 1) {
034      throw new DiskOutOfSpaceException("No more available volumes");
035    }
036    
037    // since volumes could've been removed because of the failure
038    // make sure we are not out of bounds
039    if(curVolume >= volumes.size()) {
040      curVolume = 0;
041    }
042    
043    int startVolume = curVolume;
044    long maxAvailable = 0;
045    
046    while (true) {
047      FSVolumeInterface volume = volumes.get(curVolume);
048      curVolume = (curVolume + 1) % volumes.size();
049      long availableVolumeSize = volume.getAvailable();
050      if (availableVolumeSize > blockSize) { return volume; }
051      
052      if (availableVolumeSize > maxAvailable) {
053        maxAvailable = availableVolumeSize;
054      }
055      
056      if (curVolume == startVolume) {
057        throw new DiskOutOfSpaceException(
058            "Insufficient space for an additional block. Volume with the most available space has "
059                + maxAvailable
060                + " bytes free, configured block size is "
061                + blockSize);
062      }
063    }
064  }
065
066}