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.fsdataset; 019 020import java.io.IOException; 021import java.util.List; 022 023import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException; 024 025/** 026 * Choose volumes in round-robin order. 027 */ 028public class RoundRobinVolumeChoosingPolicy<V extends FsVolumeSpi> 029 implements VolumeChoosingPolicy<V> { 030 031 private int curVolume = 0; 032 033 @Override 034 public synchronized V chooseVolume(final List<V> volumes, final long blockSize 035 ) throws IOException { 036 if(volumes.size() < 1) { 037 throw new DiskOutOfSpaceException("No more available volumes"); 038 } 039 040 // since volumes could've been removed because of the failure 041 // make sure we are not out of bounds 042 if(curVolume >= volumes.size()) { 043 curVolume = 0; 044 } 045 046 int startVolume = curVolume; 047 long maxAvailable = 0; 048 049 while (true) { 050 final V volume = volumes.get(curVolume); 051 curVolume = (curVolume + 1) % volumes.size(); 052 long availableVolumeSize = volume.getAvailable(); 053 if (availableVolumeSize > blockSize) { return volume; } 054 055 if (availableVolumeSize > maxAvailable) { 056 maxAvailable = availableVolumeSize; 057 } 058 059 if (curVolume == startVolume) { 060 throw new DiskOutOfSpaceException("Out of space: " 061 + "The volume with the most available space (=" + maxAvailable 062 + " B) is less than the block size (=" + blockSize + " B)."); 063 } 064 } 065 } 066}