/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hdfs.server.datanode.fsdataset;
import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_THRESHOLD_DEFAULT;
import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_THRESHOLD_KEY;
import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT;
import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
/**
* A DN volume choosing policy which takes into account the amount of free
* space on each of the available volumes when considering where to assign a
* new replica allocation. By default this policy prefers assigning replicas to
* those volumes with more available free space, so as to over time balance the
* available space of all the volumes within a DN.
*/
public class AvailableSpaceVolumeChoosingPolicy<V extends FsVolumeSpi>
implements VolumeChoosingPolicy<V>, Configurable {
private static final Log LOG = LogFactory.getLog(AvailableSpaceVolumeChoosingPolicy.class);
private static final Random RAND = new Random();
private long balancedSpaceThreshold = DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_THRESHOLD_DEFAULT;
private float balancedPreferencePercent = DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT;
@Override
public synchronized void setConf(Configuration conf) {
balancedSpaceThreshold = conf.getLong(
DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_THRESHOLD_KEY,
DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_THRESHOLD_DEFAULT);
balancedPreferencePercent = conf.getFloat(
DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY,
DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT);
LOG.info("Available space volume choosing policy initialized: " +
DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_THRESHOLD_KEY +
" = " + balancedSpaceThreshold + ", " +
DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY +
" = " + balancedPreferencePercent);
if (balancedPreferencePercent > 1.0) {
LOG.warn("The value of " + DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY +
" is greater than 1.0 but should be in the range 0.0 - 1.0");
}
if (balancedPreferencePercent < 0.5) {
LOG.warn("The value of " + DFS_DATANODE_AVAILABLE_SPACE_VOLUME_CHOOSING_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY +
" is less than 0.5 so volumes with less available disk space will receive more block allocations");
}
}
@Override
public synchronized Configuration getConf() {
// Nothing to do. Only added to fulfill the Configurable contract.
return null;
}
private final VolumeChoosingPolicy<V> roundRobinPolicyBalanced =
new RoundRobinVolumeChoosingPolicy<V>();
private final VolumeChoosingPolicy<V> roundRobinPolicyHighAvailable =
new RoundRobinVolumeChoosingPolicy<V>();
private final VolumeChoosingPolicy<V> roundRobinPolicyLowAvailable =
new RoundRobinVolumeChoosingPolicy<V>();
@Override
public synchronized V chooseVolume(List<V> volumes,
final long replicaSize) throws IOException {
if (volumes.size() < 1) {
throw new DiskOutOfSpaceException("No more available volumes");
}
AvailableSpaceVolumeList volumesWithSpaces =
new AvailableSpaceVolumeList(volumes);
if (volumesWithSpaces.areAllVolumesWithinFreeSpaceThreshold()) {
// If they're actually not too far out of whack, fall back on pure round
// robin.
V volume = roundRobinPolicyBalanced.chooseVolume(volumes, replicaSize);
if (LOG.isDebugEnabled()) {
LOG.debug("All volumes are within the configured free space balance " +
"threshold. Selecting " + volume + " for write of block size " +
replicaSize);
}
return volume;
} else {
V volume = null;
// If none of the volumes with low free space have enough space for the
// replica, always try to choose a volume with a lot of free space.
long mostAvailableAmongLowVolumes = volumesWithSpaces
.getMostAvailableSpaceAmongVolumesWithLowAvailableSpace();
List<V> highAvailableVolumes = extractVolumesFromPairs(
volumesWithSpaces.getVolumesWithHighAvailableSpace());
List<V> lowAvailableVolumes = extractVolumesFromPairs(
volumesWithSpaces.getVolumesWithLowAvailableSpace());
float preferencePercentScaler =
(highAvailableVolumes.size() * balancedPreferencePercent) +
(lowAvailableVolumes.size() * (1 - balancedPreferencePercent));
float scaledPreferencePercent =
(highAvailableVolumes.size() * balancedPreferencePercent) /
preferencePercentScaler;
if (mostAvailableAmongLowVolumes < replicaSize ||
RAND.nextFloat() < scaledPreferencePercent) {
volume = roundRobinPolicyHighAvailable.chooseVolume(
highAvailableVolumes,
replicaSize);
if (LOG.isDebugEnabled()) {
LOG.debug("Volumes are imbalanced. Selecting " + volume +
" from high available space volumes for write of block size "
+ replicaSize);
}
} else {
volume = roundRobinPolicyLowAvailable.chooseVolume(
lowAvailableVolumes,
replicaSize);
if (LOG.isDebugEnabled()) {
LOG.debug("Volumes are imbalanced. Selecting " + volume +
" from low available space volumes for write of block size "
+ replicaSize);
}
}
return volume;
}
}
/**
* Used to keep track of the list of volumes we're choosing from.
*/
private class AvailableSpaceVolumeList {
private final List<AvailableSpaceVolumePair> volumes;
public AvailableSpaceVolumeList(List<V> volumes) throws IOException {
this.volumes = new ArrayList<AvailableSpaceVolumePair>();
for (V volume : volumes) {
this.volumes.add(new AvailableSpaceVolumePair(volume));
}
}
/**
* Check if the available space on all the volumes is roughly equal.
*
* @param volumes the volumes to check
* @return true if all volumes' free space is within the configured threshold,
* false otherwise.
* @throws IOException
* in the event of error checking amount of available space
*/
public boolean areAllVolumesWithinFreeSpaceThreshold() {
long leastAvailable = Long.MAX_VALUE;
long mostAvailable = 0;
for (AvailableSpaceVolumePair volume : volumes) {
leastAvailable = Math.min(leastAvailable, volume.getAvailable());
mostAvailable = Math.max(mostAvailable, volume.getAvailable());
}
return (mostAvailable - leastAvailable) < balancedSpaceThreshold;
}
/**
* @return the minimum amount of space available on a single volume,
* across all volumes.
*/
private long getLeastAvailableSpace() {
long leastAvailable = Long.MAX_VALUE;
for (AvailableSpaceVolumePair volume : volumes) {
leastAvailable = Math.min(leastAvailable, volume.getAvailable());
}
return leastAvailable;
}
/**
* @return the maximum amount of space available across volumes with low space.
*/
public long getMostAvailableSpaceAmongVolumesWithLowAvailableSpace() {
long mostAvailable = Long.MIN_VALUE;
for (AvailableSpaceVolumePair volume : getVolumesWithLowAvailableSpace()) {
mostAvailable = Math.max(mostAvailable, volume.getAvailable());
}
return mostAvailable;
}
/**
* @return the list of volumes with relatively low available space.
*/
public List<AvailableSpaceVolumePair> getVolumesWithLowAvailableSpace() {
long leastAvailable = getLeastAvailableSpace();
List<AvailableSpaceVolumePair> ret = new ArrayList<AvailableSpaceVolumePair>();
for (AvailableSpaceVolumePair volume : volumes) {
if (volume.getAvailable() <= leastAvailable + balancedSpaceThreshold) {
ret.add(volume);
}
}
return ret;
}
/**
* @return the list of volumes with a lot of available space.
*/
public List<AvailableSpaceVolumePair> getVolumesWithHighAvailableSpace() {
long leastAvailable = getLeastAvailableSpace();
List<AvailableSpaceVolumePair> ret = new ArrayList<AvailableSpaceVolumePair>();
for (AvailableSpaceVolumePair volume : volumes) {
if (volume.getAvailable() > leastAvailable + balancedSpaceThreshold) {
ret.add(volume);
}
}
return ret;
}
}
/**
* Used so that we only check the available space on a given volume once, at
* the beginning of {@link AvailableSpaceVolumeChoosingPolicy#chooseVolume(List, long)}.
*/
private class AvailableSpaceVolumePair {
private final V volume;
private final long availableSpace;
public AvailableSpaceVolumePair(V volume) throws IOException {
this.volume = volume;
this.availableSpace = volume.getAvailable();
}
public long getAvailable() {
return availableSpace;
}
public V getVolume() {
return volume;
}
}
private List<V> extractVolumesFromPairs(List<AvailableSpaceVolumePair> volumes) {
List<V> ret = new ArrayList<V>();
for (AvailableSpaceVolumePair volume : volumes) {
ret.add(volume.getVolume());
}
return ret;
}
}