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/**
* 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.protocol;
import java.util.Arrays;
import java.util.EnumSet;
import java.util.LinkedList;
import java.util.List;
import com.google.common.annotations.VisibleForTesting;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.fs.BlockStoragePolicySpi;
import org.apache.hadoop.fs.StorageType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A block storage policy describes how to select the storage types
* for the replicas of a block.
*/
@InterfaceAudience.Private
public class BlockStoragePolicy implements BlockStoragePolicySpi {
public static final Logger LOG = LoggerFactory.getLogger(BlockStoragePolicy
.class);
/** A 4-bit policy ID */
private final byte id;
/** Policy name */
private final String name;
/** The storage types to store the replicas of a new block. */
private final StorageType[] storageTypes;
/** The fallback storage type for block creation. */
private final StorageType[] creationFallbacks;
/** The fallback storage type for replication. */
private final StorageType[] replicationFallbacks;
/**
* Whether the policy is inherited during file creation.
* If set then the policy cannot be changed after file creation.
*/
private boolean copyOnCreateFile;
@VisibleForTesting
public BlockStoragePolicy(byte id, String name, StorageType[] storageTypes,
StorageType[] creationFallbacks, StorageType[] replicationFallbacks) {
this(id, name, storageTypes, creationFallbacks, replicationFallbacks,
false);
}
@VisibleForTesting
public BlockStoragePolicy(byte id, String name, StorageType[] storageTypes,
StorageType[] creationFallbacks, StorageType[] replicationFallbacks,
boolean copyOnCreateFile) {
this.id = id;
this.name = name;
this.storageTypes = storageTypes;
this.creationFallbacks = creationFallbacks;
this.replicationFallbacks = replicationFallbacks;
this.copyOnCreateFile = copyOnCreateFile;
}
/**
* @return a list of {@link StorageType}s for storing the replicas of a block.
*/
public List chooseStorageTypes(final short replication) {
final List types = new LinkedList<>();
int i = 0, j = 0;
// Do not return transient storage types. We will not have accurate
// usage information for transient types.
for (;i < replication && j < storageTypes.length; ++j) {
if (!storageTypes[j].isTransient()) {
types.add(storageTypes[j]);
++i;
}
}
final StorageType last = storageTypes[storageTypes.length - 1];
if (!last.isTransient()) {
for (; i < replication; i++) {
types.add(last);
}
}
return types;
}
/**
* Choose the storage types for storing the remaining replicas, given the
* replication number and the storage types of the chosen replicas.
*
* @param replication the replication number.
* @param chosen the storage types of the chosen replicas.
* @return a list of {@link StorageType}s for storing the replicas of a block.
*/
public List chooseStorageTypes(final short replication,
final Iterable chosen) {
return chooseStorageTypes(replication, chosen, null);
}
private List chooseStorageTypes(final short replication,
final Iterable chosen, final List excess) {
final List types = chooseStorageTypes(replication);
diff(types, chosen, excess);
return types;
}
/**
* Choose the storage types for storing the remaining replicas, given the
* replication number, the storage types of the chosen replicas and
* the unavailable storage types. It uses fallback storage in case that
* the desired storage type is unavailable.
*
* @param replication the replication number.
* @param chosen the storage types of the chosen replicas.
* @param unavailables the unavailable storage types.
* @param isNewBlock Is it for new block creation?
* @return a list of {@link StorageType}s for storing the replicas of a block.
*/
public List chooseStorageTypes(final short replication,
final Iterable chosen,
final EnumSet unavailables,
final boolean isNewBlock) {
final List excess = new LinkedList<>();
final List storageTypes = chooseStorageTypes(
replication, chosen, excess);
final int expectedSize = storageTypes.size() - excess.size();
final List removed = new LinkedList<>();
for(int i = storageTypes.size() - 1; i >= 0; i--) {
// replace/remove unavailable storage types.
final StorageType t = storageTypes.get(i);
if (unavailables.contains(t)) {
final StorageType fallback = isNewBlock?
getCreationFallback(unavailables)
: getReplicationFallback(unavailables);
if (fallback == null) {
removed.add(storageTypes.remove(i));
} else {
storageTypes.set(i, fallback);
}
}
}
// remove excess storage types after fallback replacement.
diff(storageTypes, excess, null);
if (storageTypes.size() < expectedSize) {
LOG.warn("Failed to place enough replicas: expected size is {}"
+ " but only {} storage types can be selected (replication={},"
+ " selected={}, unavailable={}" + ", removed={}" + ", policy={}"
+ ")", expectedSize, storageTypes.size(), replication, storageTypes,
unavailables, removed, this);
}
return storageTypes;
}
/**
* Compute the difference between two lists t and c so that after the diff
* computation we have: t = t - c;
* Further, if e is not null, set e = e + c - t;
*/
private static void diff(List t, Iterable c,
List e) {
for(StorageType storagetype : c) {
final int i = t.indexOf(storagetype);
if (i >= 0) {
t.remove(i);
} else if (e != null) {
e.add(storagetype);
}
}
}
/**
* Choose excess storage types for deletion, given the
* replication number and the storage types of the chosen replicas.
*
* @param replication the replication number.
* @param chosen the storage types of the chosen replicas.
* @return a list of {@link StorageType}s for deletion.
*/
public List chooseExcess(final short replication,
final Iterable chosen) {
final List types = chooseStorageTypes(replication);
final List excess = new LinkedList<>();
diff(types, chosen, excess);
return excess;
}
/** @return the fallback {@link StorageType} for creation. */
public StorageType getCreationFallback(EnumSet unavailables) {
return getFallback(unavailables, creationFallbacks);
}
/** @return the fallback {@link StorageType} for replication. */
public StorageType getReplicationFallback(EnumSet unavailables) {
return getFallback(unavailables, replicationFallbacks);
}
@Override
public int hashCode() {
return Byte.valueOf(id).hashCode();
}
@Override
public boolean equals(Object obj) {
if (obj == this) {
return true;
} else if (obj == null || !(obj instanceof BlockStoragePolicy)) {
return false;
}
final BlockStoragePolicy that = (BlockStoragePolicy)obj;
return this.id == that.id;
}
@Override
public String toString() {
return getClass().getSimpleName() + "{" + name + ":" + id
+ ", storageTypes=" + Arrays.asList(storageTypes)
+ ", creationFallbacks=" + Arrays.asList(creationFallbacks)
+ ", replicationFallbacks=" + Arrays.asList(replicationFallbacks) + "}";
}
public byte getId() {
return id;
}
@Override
public String getName() {
return name;
}
@Override
public StorageType[] getStorageTypes() {
return this.storageTypes;
}
@Override
public StorageType[] getCreationFallbacks() {
return this.creationFallbacks;
}
@Override
public StorageType[] getReplicationFallbacks() {
return this.replicationFallbacks;
}
private static StorageType getFallback(EnumSet unavailables,
StorageType[] fallbacks) {
for(StorageType fb : fallbacks) {
if (!unavailables.contains(fb)) {
return fb;
}
}
return null;
}
@Override
public boolean isCopyOnCreateFile() {
return copyOnCreateFile;
}
}
