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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.server.blockmanagement;
import static org.apache.hadoop.util.Time.now;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
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.DFSConfigKeys;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.hdfs.protocol.HdfsConstants;
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.net.NodeBase;
import com.google.common.annotations.VisibleForTesting;
/**
* The class is responsible for choosing the desired number of targets
* for placing block replicas.
* The replica placement strategy is that if the writer is on a datanode,
* the 1st replica is placed on the local machine,
* otherwise a random datanode. The 2nd replica is placed on a datanode
* that is on a different rack. The 3rd replica is placed on a datanode
* which is on a different node of the rack as the second replica.
*/
@InterfaceAudience.Private
public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
private static final Log LOG =
LogFactory.getLog(BlockPlacementPolicyDefault.class.getName());
private static final String enableDebugLogging =
"For more information, please enable DEBUG log level on "
+ LOG.getClass().getName();
protected boolean considerLoad;
private boolean preferLocalNode = true;
protected NetworkTopology clusterMap;
private FSClusterStats stats;
private long heartbeatInterval; // interval for DataNode heartbeats
private long staleInterval; // interval used to identify stale DataNodes
/**
* A miss of that many heartbeats is tolerated for replica deletion policy.
*/
protected int tolerateHeartbeatMultiplier;
BlockPlacementPolicyDefault(Configuration conf, FSClusterStats stats,
NetworkTopology clusterMap) {
initialize(conf, stats, clusterMap);
}
protected BlockPlacementPolicyDefault() {
}
@Override
public void initialize(Configuration conf, FSClusterStats stats,
NetworkTopology clusterMap) {
this.considerLoad = conf.getBoolean(
DFSConfigKeys.DFS_NAMENODE_REPLICATION_CONSIDERLOAD_KEY, true);
this.stats = stats;
this.clusterMap = clusterMap;
this.heartbeatInterval = conf.getLong(
DFSConfigKeys.DFS_HEARTBEAT_INTERVAL_KEY,
DFSConfigKeys.DFS_HEARTBEAT_INTERVAL_DEFAULT) * 1000;
this.tolerateHeartbeatMultiplier = conf.getInt(
DFSConfigKeys.DFS_NAMENODE_TOLERATE_HEARTBEAT_MULTIPLIER_KEY,
DFSConfigKeys.DFS_NAMENODE_TOLERATE_HEARTBEAT_MULTIPLIER_DEFAULT);
this.staleInterval = conf.getLong(
DFSConfigKeys.DFS_NAMENODE_STALE_DATANODE_INTERVAL_KEY,
DFSConfigKeys.DFS_NAMENODE_STALE_DATANODE_INTERVAL_DEFAULT);
}
protected ThreadLocal threadLocalBuilder =
new ThreadLocal() {
@Override
protected StringBuilder initialValue() {
return new StringBuilder();
}
};
@Override
public DatanodeDescriptor[] chooseTarget(String srcPath,
int numOfReplicas,
DatanodeDescriptor writer,
List chosenNodes,
long blocksize) {
return chooseTarget(numOfReplicas, writer, chosenNodes, false,
null, blocksize);
}
@Override
public DatanodeDescriptor[] chooseTarget(String srcPath,
int numOfReplicas,
DatanodeDescriptor writer,
List chosenNodes,
boolean returnChosenNodes,
HashMap excludedNodes,
long blocksize) {
return chooseTarget(numOfReplicas, writer, chosenNodes, returnChosenNodes,
excludedNodes, blocksize);
}
/** This is the implementation. */
DatanodeDescriptor[] chooseTarget(int numOfReplicas,
DatanodeDescriptor writer,
List chosenNodes,
boolean returnChosenNodes,
HashMap excludedNodes,
long blocksize) {
if (numOfReplicas == 0 || clusterMap.getNumOfLeaves()==0) {
return new DatanodeDescriptor[0];
}
if (excludedNodes == null) {
excludedNodes = new HashMap();
}
int clusterSize = clusterMap.getNumOfLeaves();
int totalNumOfReplicas = chosenNodes.size()+numOfReplicas;
if (totalNumOfReplicas > clusterSize) {
numOfReplicas -= (totalNumOfReplicas-clusterSize);
totalNumOfReplicas = clusterSize;
}
int maxNodesPerRack =
(totalNumOfReplicas-1)/clusterMap.getNumOfRacks()+2;
List results =
new ArrayList(chosenNodes);
for (Node node:chosenNodes) {
excludedNodes.put(node, node);
}
if (!clusterMap.contains(writer)) {
writer=null;
}
boolean avoidStaleNodes = (stats != null
&& stats.isAvoidingStaleDataNodesForWrite());
DatanodeDescriptor localNode = chooseTarget(numOfReplicas, writer,
excludedNodes, blocksize, maxNodesPerRack, results, avoidStaleNodes);
if (!returnChosenNodes) {
results.removeAll(chosenNodes);
}
// sorting nodes to form a pipeline
return getPipeline((writer==null)?localNode:writer,
results.toArray(new DatanodeDescriptor[results.size()]));
}
/* choose numOfReplicas from all data nodes */
private DatanodeDescriptor chooseTarget(int numOfReplicas,
DatanodeDescriptor writer,
HashMap excludedNodes,
long blocksize,
int maxNodesPerRack,
List results,
final boolean avoidStaleNodes) {
if (numOfReplicas == 0 || clusterMap.getNumOfLeaves()==0) {
return writer;
}
int totalReplicasExpected = numOfReplicas + results.size();
int numOfResults = results.size();
boolean newBlock = (numOfResults==0);
if (writer == null && !newBlock) {
writer = results.get(0);
}
// Keep a copy of original excludedNodes
final HashMap oldExcludedNodes = avoidStaleNodes ?
new HashMap(excludedNodes) : null;
try {
if (numOfResults == 0) {
writer = chooseLocalNode(writer, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
if (--numOfReplicas == 0) {
return writer;
}
}
if (numOfResults <= 1) {
chooseRemoteRack(1, results.get(0), excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
if (--numOfReplicas == 0) {
return writer;
}
}
if (numOfResults <= 2) {
if (clusterMap.isOnSameRack(results.get(0), results.get(1))) {
chooseRemoteRack(1, results.get(0), excludedNodes,
blocksize, maxNodesPerRack,
results, avoidStaleNodes);
} else if (newBlock){
chooseLocalRack(results.get(1), excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
} else {
chooseLocalRack(writer, excludedNodes, blocksize, maxNodesPerRack,
results, avoidStaleNodes);
}
if (--numOfReplicas == 0) {
return writer;
}
}
chooseRandom(numOfReplicas, NodeBase.ROOT, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
} catch (NotEnoughReplicasException e) {
LOG.warn("Not able to place enough replicas, still in need of "
+ (totalReplicasExpected - results.size()) + " to reach "
+ totalReplicasExpected + "\n"
+ e.getMessage());
if (avoidStaleNodes) {
// Retry chooseTarget again, this time not avoiding stale nodes.
// excludedNodes contains the initial excludedNodes and nodes that were
// not chosen because they were stale, decommissioned, etc.
// We need to additionally exclude the nodes that were added to the
// result list in the successful calls to choose*() above.
for (Node node : results) {
oldExcludedNodes.put(node, node);
}
// Set numOfReplicas, since it can get out of sync with the result list
// if the NotEnoughReplicasException was thrown in chooseRandom().
numOfReplicas = totalReplicasExpected - results.size();
return chooseTarget(numOfReplicas, writer, oldExcludedNodes, blocksize,
maxNodesPerRack, results, false);
}
}
return writer;
}
/* choose localMachine as the target.
* if localMachine is not available,
* choose a node on the same rack
* @return the chosen node
*/
protected DatanodeDescriptor chooseLocalNode(
DatanodeDescriptor localMachine,
HashMap excludedNodes,
long blocksize,
int maxNodesPerRack,
List results,
boolean avoidStaleNodes)
throws NotEnoughReplicasException {
// if no local machine, randomly choose one node
if (localMachine == null)
return chooseRandom(NodeBase.ROOT, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
if (preferLocalNode) {
// otherwise try local machine first
Node oldNode = excludedNodes.put(localMachine, localMachine);
if (oldNode == null) { // was not in the excluded list
if (isGoodTarget(localMachine, blocksize, maxNodesPerRack, false,
results, avoidStaleNodes)) {
results.add(localMachine);
return localMachine;
}
}
}
// try a node on local rack
return chooseLocalRack(localMachine, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
}
/* choose one node from the rack that localMachine is on.
* if no such node is available, choose one node from the rack where
* a second replica is on.
* if still no such node is available, choose a random node
* in the cluster.
* @return the chosen node
*/
protected DatanodeDescriptor chooseLocalRack(
DatanodeDescriptor localMachine,
HashMap excludedNodes,
long blocksize,
int maxNodesPerRack,
List results,
boolean avoidStaleNodes)
throws NotEnoughReplicasException {
// no local machine, so choose a random machine
if (localMachine == null) {
return chooseRandom(NodeBase.ROOT, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
}
// choose one from the local rack
try {
return chooseRandom(localMachine.getNetworkLocation(), excludedNodes,
blocksize, maxNodesPerRack, results, avoidStaleNodes);
} catch (NotEnoughReplicasException e1) {
// find the second replica
DatanodeDescriptor newLocal=null;
for(Iterator iter=results.iterator();
iter.hasNext();) {
DatanodeDescriptor nextNode = iter.next();
if (nextNode != localMachine) {
newLocal = nextNode;
break;
}
}
if (newLocal != null) {
try {
return chooseRandom(newLocal.getNetworkLocation(), excludedNodes,
blocksize, maxNodesPerRack, results, avoidStaleNodes);
} catch(NotEnoughReplicasException e2) {
//otherwise randomly choose one from the network
return chooseRandom(NodeBase.ROOT, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
}
} else {
//otherwise randomly choose one from the network
return chooseRandom(NodeBase.ROOT, excludedNodes, blocksize,
maxNodesPerRack, results, avoidStaleNodes);
}
}
}
/* choose numOfReplicas nodes from the racks
* that localMachine is NOT on.
* if not enough nodes are available, choose the remaining ones
* from the local rack
*/
protected void chooseRemoteRack(int numOfReplicas,
DatanodeDescriptor localMachine,
HashMap excludedNodes,
long blocksize,
int maxReplicasPerRack,
List results,
boolean avoidStaleNodes)
throws NotEnoughReplicasException {
int oldNumOfReplicas = results.size();
// randomly choose one node from remote racks
try {
chooseRandom(numOfReplicas, "~" + localMachine.getNetworkLocation(),
excludedNodes, blocksize, maxReplicasPerRack, results,
avoidStaleNodes);
} catch (NotEnoughReplicasException e) {
chooseRandom(numOfReplicas-(results.size()-oldNumOfReplicas),
localMachine.getNetworkLocation(), excludedNodes, blocksize,
maxReplicasPerRack, results, avoidStaleNodes);
}
}
/* Randomly choose one target from nodes.
* @return the chosen node
*/
protected DatanodeDescriptor chooseRandom(
String nodes,
HashMap excludedNodes,
long blocksize,
int maxNodesPerRack,
List results,
boolean avoidStaleNodes)
throws NotEnoughReplicasException {
int numOfAvailableNodes =
clusterMap.countNumOfAvailableNodes(nodes, excludedNodes.keySet());
StringBuilder builder = null;
if (LOG.isDebugEnabled()) {
builder = threadLocalBuilder.get();
builder.setLength(0);
builder.append("[");
}
boolean badTarget = false;
while(numOfAvailableNodes > 0) {
DatanodeDescriptor chosenNode =
(DatanodeDescriptor)(clusterMap.chooseRandom(nodes));
Node oldNode = excludedNodes.put(chosenNode, chosenNode);
if (oldNode == null) { // choosendNode was not in the excluded list
numOfAvailableNodes--;
if (isGoodTarget(chosenNode, blocksize,
maxNodesPerRack, results, avoidStaleNodes)) {
results.add(chosenNode);
return chosenNode;
} else {
badTarget = true;
}
}
}
String detail = enableDebugLogging;
if (LOG.isDebugEnabled()) {
if (badTarget && builder != null) {
detail = builder.append("]").toString();
builder.setLength(0);
} else detail = "";
}
throw new NotEnoughReplicasException(detail);
}
/* Randomly choose numOfReplicas targets from nodes.
*/
protected void chooseRandom(int numOfReplicas,
String nodes,
HashMap excludedNodes,
long blocksize,
int maxNodesPerRack,
List results,
boolean avoidStaleNodes)
throws NotEnoughReplicasException {
int numOfAvailableNodes =
clusterMap.countNumOfAvailableNodes(nodes, excludedNodes.keySet());
StringBuilder builder = null;
if (LOG.isDebugEnabled()) {
builder = threadLocalBuilder.get();
builder.setLength(0);
builder.append("[");
}
boolean badTarget = false;
while(numOfReplicas > 0 && numOfAvailableNodes > 0) {
DatanodeDescriptor chosenNode =
(DatanodeDescriptor)(clusterMap.chooseRandom(nodes));
Node oldNode = excludedNodes.put(chosenNode, chosenNode);
if (oldNode == null) {
numOfAvailableNodes--;
if (isGoodTarget(chosenNode, blocksize,
maxNodesPerRack, results, avoidStaleNodes)) {
numOfReplicas--;
results.add(chosenNode);
} else {
badTarget = true;
}
}
}
if (numOfReplicas>0) {
String detail = enableDebugLogging;
if (LOG.isDebugEnabled()) {
if (badTarget && builder != null) {
detail = builder.append("]").toString();
builder.setLength(0);
} else detail = "";
}
throw new NotEnoughReplicasException(detail);
}
}
/* judge if a node is a good target.
* return true if node has enough space,
* does not have too much load, and the rack does not have too many nodes
*/
private boolean isGoodTarget(DatanodeDescriptor node,
long blockSize, int maxTargetPerRack,
List results,
boolean avoidStaleNodes) {
return isGoodTarget(node, blockSize, maxTargetPerRack, this.considerLoad,
results, avoidStaleNodes);
}
/**
* Determine if a node is a good target.
*
* @param node The target node
* @param blockSize Size of block
* @param maxTargetPerRack Maximum number of targets per rack. The value of
* this parameter depends on the number of racks in
* the cluster and total number of replicas for a block
* @param considerLoad whether or not to consider load of the target node
* @param results A list containing currently chosen nodes. Used to check if
* too many nodes has been chosen in the target rack.
* @param avoidStaleNodes Whether or not to avoid choosing stale nodes
* @return Return true if node has enough space,
* does not have too much load,
* and the rack does not have too many nodes.
*/
protected boolean isGoodTarget(DatanodeDescriptor node,
long blockSize, int maxTargetPerRack,
boolean considerLoad,
List results,
boolean avoidStaleNodes) {
// check if the node is (being) decommissed
if (node.isDecommissionInProgress() || node.isDecommissioned()) {
if(LOG.isDebugEnabled()) {
threadLocalBuilder.get().append(node.toString()).append(": ")
.append("Node ").append(NodeBase.getPath(node))
.append(" is not chosen because the node is (being) decommissioned ");
}
return false;
}
if (avoidStaleNodes) {
if (node.isStale(this.staleInterval)) {
if (LOG.isDebugEnabled()) {
threadLocalBuilder.get().append(node.toString()).append(": ")
.append("Node ").append(NodeBase.getPath(node))
.append(" is not chosen because the node is stale ");
}
return false;
}
}
long remaining = node.getRemaining() -
(node.getBlocksScheduled() * blockSize);
// check the remaining capacity of the target machine
if (blockSize* HdfsConstants.MIN_BLOCKS_FOR_WRITE>remaining) {
if(LOG.isDebugEnabled()) {
threadLocalBuilder.get().append(node.toString()).append(": ")
.append("Node ").append(NodeBase.getPath(node))
.append(" is not chosen because the node does not have enough space ");
}
return false;
}
// check the communication traffic of the target machine
if (considerLoad) {
double avgLoad = 0;
int size = clusterMap.getNumOfLeaves();
if (size != 0 && stats != null) {
avgLoad = (double)stats.getTotalLoad()/size;
}
if (node.getXceiverCount() > (2.0 * avgLoad)) {
if(LOG.isDebugEnabled()) {
threadLocalBuilder.get().append(node.toString()).append(": ")
.append("Node ").append(NodeBase.getPath(node))
.append(" is not chosen because the node is too busy ");
}
return false;
}
}
// check if the target rack has chosen too many nodes
String rackname = node.getNetworkLocation();
int counter=1;
for(Iterator iter = results.iterator();
iter.hasNext();) {
Node result = iter.next();
if (rackname.equals(result.getNetworkLocation())) {
counter++;
}
}
if (counter>maxTargetPerRack) {
if(LOG.isDebugEnabled()) {
threadLocalBuilder.get().append(node.toString()).append(": ")
.append("Node ").append(NodeBase.getPath(node))
.append(" is not chosen because the rack has too many chosen nodes ");
}
return false;
}
return true;
}
/* Return a pipeline of nodes.
* The pipeline is formed finding a shortest path that
* starts from the writer and traverses all nodes
* This is basically a traveling salesman problem.
*/
private DatanodeDescriptor[] getPipeline(
DatanodeDescriptor writer,
DatanodeDescriptor[] nodes) {
if (nodes.length==0) return nodes;
synchronized(clusterMap) {
int index=0;
if (writer == null || !clusterMap.contains(writer)) {
writer = nodes[0];
}
for(;indexcurrentDistance) {
shortestDistance = currentDistance;
shortestNode = currentNode;
shortestIndex = i;
}
}
//switch position index & shortestIndex
if (index != shortestIndex) {
nodes[shortestIndex] = nodes[index];
nodes[index] = shortestNode;
}
writer = shortestNode;
}
}
return nodes;
}
@Override
public int verifyBlockPlacement(String srcPath,
LocatedBlock lBlk,
int minRacks) {
DatanodeInfo[] locs = lBlk.getLocations();
if (locs == null)
locs = new DatanodeInfo[0];
int numRacks = clusterMap.getNumOfRacks();
if(numRacks <= 1) // only one rack
return 0;
minRacks = Math.min(minRacks, numRacks);
// 1. Check that all locations are different.
// 2. Count locations on different racks.
Set racks = new TreeSet();
for (DatanodeInfo dn : locs)
racks.add(dn.getNetworkLocation());
return minRacks - racks.size();
}
@Override
public DatanodeDescriptor chooseReplicaToDelete(BlockCollection bc,
Block block,
short replicationFactor,
Collection first,
Collection second) {
long oldestHeartbeat =
now() - heartbeatInterval * tolerateHeartbeatMultiplier;
DatanodeDescriptor oldestHeartbeatNode = null;
long minSpace = Long.MAX_VALUE;
DatanodeDescriptor minSpaceNode = null;
// pick replica from the first Set. If first is empty, then pick replicas
// from second set.
Iterator iter = pickupReplicaSet(first, second);
// Pick the node with the oldest heartbeat or with the least free space,
// if all hearbeats are within the tolerable heartbeat interval
while (iter.hasNext() ) {
DatanodeDescriptor node = iter.next();
long free = node.getRemaining();
long lastHeartbeat = node.getLastUpdate();
if(lastHeartbeat < oldestHeartbeat) {
oldestHeartbeat = lastHeartbeat;
oldestHeartbeatNode = node;
}
if (minSpace > free) {
minSpace = free;
minSpaceNode = node;
}
}
return oldestHeartbeatNode != null ? oldestHeartbeatNode : minSpaceNode;
}
/**
* Pick up replica node set for deleting replica as over-replicated.
* First set contains replica nodes on rack with more than one
* replica while second set contains remaining replica nodes.
* So pick up first set if not empty. If first is empty, then pick second.
*/
protected Iterator pickupReplicaSet(
Collection first,
Collection second) {
Iterator iter =
first.isEmpty() ? second.iterator() : first.iterator();
return iter;
}
@VisibleForTesting
void setPreferLocalNode(boolean prefer) {
this.preferLocalNode = prefer;
}
}
