/**
* 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.blockmanagement;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.hdfs.protocol.LocatedBlock;
import org.apache.hadoop.hdfs.server.namenode.FSClusterStats;
import org.apache.hadoop.net.NetworkTopology;
import org.apache.hadoop.net.Node;
import org.apache.hadoop.util.ReflectionUtils;
/**
* This interface is used for choosing the desired number of targets
* for placing block replicas.
*/
@InterfaceAudience.Private
public abstract class BlockPlacementPolicy {
static final Log LOG = LogFactory.getLog(BlockPlacementPolicy.class);
@InterfaceAudience.Private
public static class NotEnoughReplicasException extends Exception {
private static final long serialVersionUID = 1L;
NotEnoughReplicasException(String msg) {
super(msg);
}
}
/**
* choose <i>numOfReplicas</i> data nodes for <i>writer</i>
* to re-replicate a block with size <i>blocksize</i>
* If not, return as many as we can.
*
* @param srcPath the file to which this chooseTargets is being invoked.
* @param numOfReplicas additional number of replicas wanted.
* @param writer the writer's machine, null if not in the cluster.
* @param chosenNodes datanodes that have been chosen as targets.
* @param blocksize size of the data to be written.
* @return array of DatanodeDescriptor instances chosen as target
* and sorted as a pipeline.
*/
abstract DatanodeDescriptor[] chooseTarget(String srcPath,
int numOfReplicas,
DatanodeDescriptor writer,
List<DatanodeDescriptor> chosenNodes,
long blocksize);
/**
* choose <i>numOfReplicas</i> data nodes for <i>writer</i>
* to re-replicate a block with size <i>blocksize</i>
* If not, return as many as we can.
*
* @param srcPath the file to which this chooseTargets is being invoked.
* @param numOfReplicas additional number of replicas wanted.
* @param writer the writer's machine, null if not in the cluster.
* @param chosenNodes datanodes that have been chosen as targets.
* @param returnChosenNodes decide if the chosenNodes are returned.
* @param excludedNodes datanodes that should not be considered as targets.
* @param blocksize size of the data to be written.
* @return array of DatanodeDescriptor instances chosen as target
* and sorted as a pipeline.
*/
public abstract DatanodeDescriptor[] chooseTarget(String srcPath,
int numOfReplicas,
DatanodeDescriptor writer,
List<DatanodeDescriptor> chosenNodes,
boolean returnChosenNodes,
HashMap<Node, Node> excludedNodes,
long blocksize);
/**
* choose <i>numOfReplicas</i> data nodes for <i>writer</i>
* If not, return as many as we can.
* The base implemenatation extracts the pathname of the file from the
* specified srcBC, but this could be a costly operation depending on the
* file system implementation. Concrete implementations of this class should
* override this method to avoid this overhead.
*
* @param srcBC block collection of file for which chooseTarget is invoked.
* @param numOfReplicas additional number of replicas wanted.
* @param writer the writer's machine, null if not in the cluster.
* @param chosenNodes datanodes that have been chosen as targets.
* @param blocksize size of the data to be written.
* @return array of DatanodeDescriptor instances chosen as target
* and sorted as a pipeline.
*/
DatanodeDescriptor[] chooseTarget(BlockCollection srcBC,
int numOfReplicas,
DatanodeDescriptor writer,
List<DatanodeDescriptor> chosenNodes,
HashMap<Node, Node> excludedNodes,
long blocksize) {
return chooseTarget(srcBC.getName(), numOfReplicas, writer,
chosenNodes, false, excludedNodes, blocksize);
}
/**
* Same as {@link #chooseTarget(String, int, DatanodeDescriptor, List, boolean,
* HashMap, long)} with added parameter {@code favoredDatanodes}
* @param favoredNodes datanodes that should be favored as targets. This
* is only a hint and due to cluster state, namenode may not be
* able to place the blocks on these datanodes.
*/
DatanodeDescriptor[] chooseTarget(String src,
int numOfReplicas, DatanodeDescriptor writer,
HashMap<Node, Node> excludedNodes,
long blocksize, List<DatanodeDescriptor> favoredNodes) {
// This class does not provide the functionality of placing
// a block in favored datanodes. The implementations of this class
// are expected to provide this functionality
return chooseTarget(src, numOfReplicas, writer,
new ArrayList<DatanodeDescriptor>(numOfReplicas), false, excludedNodes,
blocksize);
}
/**
* Verify that the block is replicated on at least minRacks different racks
* if there is more than minRacks rack in the system.
*
* @param srcPath the full pathname of the file to be verified
* @param lBlk block with locations
* @param minRacks number of racks the block should be replicated to
* @return the difference between the required and the actual number of racks
* the block is replicated to.
*/
abstract public int verifyBlockPlacement(String srcPath,
LocatedBlock lBlk,
int minRacks);
/**
* Decide whether deleting the specified replica of the block still makes
* the block conform to the configured block placement policy.
*
* @param srcBC block collection of file to which block-to-be-deleted belongs
* @param block The block to be deleted
* @param replicationFactor The required number of replicas for this block
* @param existingReplicas The replica locations of this block that are present
on at least two unique racks.
* @param moreExistingReplicas Replica locations of this block that are not
listed in the previous parameter.
* @return the replica that is the best candidate for deletion
*/
abstract public DatanodeDescriptor chooseReplicaToDelete(BlockCollection srcBC,
Block block,
short replicationFactor,
Collection<DatanodeDescriptor> existingReplicas,
Collection<DatanodeDescriptor> moreExistingReplicas);
/**
* Used to setup a BlockPlacementPolicy object. This should be defined by
* all implementations of a BlockPlacementPolicy.
*
* @param conf the configuration object
* @param stats retrieve cluster status from here
* @param clusterMap cluster topology
*/
abstract protected void initialize(Configuration conf, FSClusterStats stats,
NetworkTopology clusterMap);
/**
* Get an instance of the configured Block Placement Policy based on the
* value of the configuration paramater dfs.block.replicator.classname.
*
* @param conf the configuration to be used
* @param stats an object that is used to retrieve the load on the cluster
* @param clusterMap the network topology of the cluster
* @return an instance of BlockPlacementPolicy
*/
public static BlockPlacementPolicy getInstance(Configuration conf,
FSClusterStats stats,
NetworkTopology clusterMap) {
Class<? extends BlockPlacementPolicy> replicatorClass =
conf.getClass("dfs.block.replicator.classname",
BlockPlacementPolicyDefault.class,
BlockPlacementPolicy.class);
BlockPlacementPolicy replicator = (BlockPlacementPolicy) ReflectionUtils.newInstance(
replicatorClass, conf);
replicator.initialize(conf, stats, clusterMap);
return replicator;
}
/**
* Adjust rackmap, moreThanOne, and exactlyOne after removing replica on cur.
*
* @param rackMap a map from rack to replica
* @param moreThanOne The List of replica nodes on rack which has more than
* one replica
* @param exactlyOne The List of replica nodes on rack with only one replica
* @param cur current replica to remove
*/
public void adjustSetsWithChosenReplica(final Map<String,
List<DatanodeDescriptor>> rackMap,
final List<DatanodeDescriptor> moreThanOne,
final List<DatanodeDescriptor> exactlyOne, final DatanodeInfo cur) {
String rack = getRack(cur);
final List<DatanodeDescriptor> datanodes = rackMap.get(rack);
datanodes.remove(cur);
if (datanodes.isEmpty()) {
rackMap.remove(rack);
}
if (moreThanOne.remove(cur)) {
if (datanodes.size() == 1) {
moreThanOne.remove(datanodes.get(0));
exactlyOne.add(datanodes.get(0));
}
} else {
exactlyOne.remove(cur);
}
}
/**
* Get rack string from a data node
* @param datanode
* @return rack of data node
*/
protected String getRack(final DatanodeInfo datanode) {
return datanode.getNetworkLocation();
}
/**
* Split data nodes into two sets, one set includes nodes on rack with
* more than one replica, the other set contains the remaining nodes.
*
* @param dataNodes
* @param rackMap a map from rack to datanodes
* @param moreThanOne contains nodes on rack with more than one replica
* @param exactlyOne remains contains the remaining nodes
*/
public void splitNodesWithRack(
Collection<DatanodeDescriptor> dataNodes,
final Map<String, List<DatanodeDescriptor>> rackMap,
final List<DatanodeDescriptor> moreThanOne,
final List<DatanodeDescriptor> exactlyOne) {
for(DatanodeDescriptor node : dataNodes) {
final String rackName = getRack(node);
List<DatanodeDescriptor> datanodeList = rackMap.get(rackName);
if (datanodeList == null) {
datanodeList = new ArrayList<DatanodeDescriptor>();
rackMap.put(rackName, datanodeList);
}
datanodeList.add(node);
}
// split nodes into two sets
for(List<DatanodeDescriptor> datanodeList : rackMap.values()) {
if (datanodeList.size() == 1) {
// exactlyOne contains nodes on rack with only one replica
exactlyOne.add(datanodeList.get(0));
} else {
// moreThanOne contains nodes on rack with more than one replica
moreThanOne.addAll(datanodeList);
}
}
}
}