/**
* 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.mapreduce.task.reduce;
import java.io.IOException;
import java.net.InetAddress;
import java.net.URI;
import java.net.UnknownHostException;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapred.Counters;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.TaskCompletionEvent;
import org.apache.hadoop.mapred.TaskStatus;
import org.apache.hadoop.mapreduce.MRJobConfig;
import org.apache.hadoop.mapreduce.TaskAttemptID;
import org.apache.hadoop.mapreduce.TaskID;
import org.apache.hadoop.mapreduce.task.reduce.MapHost.State;
import org.apache.hadoop.util.Progress;
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class ShuffleSchedulerImpl<K,V> implements ShuffleScheduler<K,V> {
static ThreadLocal<Long> shuffleStart = new ThreadLocal<Long>() {
protected Long initialValue() {
return 0L;
}
};
private static final Log LOG = LogFactory.getLog(ShuffleSchedulerImpl.class);
private static final int MAX_MAPS_AT_ONCE = 20;
private static final long INITIAL_PENALTY = 10000;
private static final float PENALTY_GROWTH_RATE = 1.3f;
private final static int REPORT_FAILURE_LIMIT = 10;
private final boolean[] finishedMaps;
private final int totalMaps;
private int remainingMaps;
private Map<String, MapHost> mapLocations = new HashMap<String, MapHost>();
private Set<MapHost> pendingHosts = new HashSet<MapHost>();
private Set<TaskAttemptID> obsoleteMaps = new HashSet<TaskAttemptID>();
private final TaskAttemptID reduceId;
private final Random random = new Random();
private final DelayQueue<Penalty> penalties = new DelayQueue<Penalty>();
private final Referee referee = new Referee();
private final Map<TaskAttemptID,IntWritable> failureCounts =
new HashMap<TaskAttemptID,IntWritable>();
private final Map<String,IntWritable> hostFailures =
new HashMap<String,IntWritable>();
private final TaskStatus status;
private final ExceptionReporter reporter;
private final int abortFailureLimit;
private final Progress progress;
private final Counters.Counter shuffledMapsCounter;
private final Counters.Counter reduceShuffleBytes;
private final Counters.Counter failedShuffleCounter;
private final long startTime;
private long lastProgressTime;
private volatile int maxMapRuntime = 0;
private final int maxFailedUniqueFetches;
private final int maxFetchFailuresBeforeReporting;
private long totalBytesShuffledTillNow = 0;
private final DecimalFormat mbpsFormat = new DecimalFormat("0.00");
private final boolean reportReadErrorImmediately;
private long maxDelay = MRJobConfig.DEFAULT_MAX_SHUFFLE_FETCH_RETRY_DELAY;
public ShuffleSchedulerImpl(JobConf job, TaskStatus status,
TaskAttemptID reduceId,
ExceptionReporter reporter,
Progress progress,
Counters.Counter shuffledMapsCounter,
Counters.Counter reduceShuffleBytes,
Counters.Counter failedShuffleCounter) {
totalMaps = job.getNumMapTasks();
abortFailureLimit = Math.max(30, totalMaps / 10);
remainingMaps = totalMaps;
finishedMaps = new boolean[remainingMaps];
this.reporter = reporter;
this.status = status;
this.reduceId = reduceId;
this.progress = progress;
this.shuffledMapsCounter = shuffledMapsCounter;
this.reduceShuffleBytes = reduceShuffleBytes;
this.failedShuffleCounter = failedShuffleCounter;
this.startTime = System.currentTimeMillis();
lastProgressTime = startTime;
referee.start();
this.maxFailedUniqueFetches = Math.min(totalMaps, 5);
this.maxFetchFailuresBeforeReporting = job.getInt(
MRJobConfig.SHUFFLE_FETCH_FAILURES, REPORT_FAILURE_LIMIT);
this.reportReadErrorImmediately = job.getBoolean(
MRJobConfig.SHUFFLE_NOTIFY_READERROR, true);
this.maxDelay = job.getLong(MRJobConfig.MAX_SHUFFLE_FETCH_RETRY_DELAY,
MRJobConfig.DEFAULT_MAX_SHUFFLE_FETCH_RETRY_DELAY);
}
@Override
public void resolve(TaskCompletionEvent event) {
switch (event.getTaskStatus()) {
case SUCCEEDED:
URI u = getBaseURI(reduceId, event.getTaskTrackerHttp());
addKnownMapOutput(u.getHost() + ":" + u.getPort(),
u.toString(),
event.getTaskAttemptId());
maxMapRuntime = Math.max(maxMapRuntime, event.getTaskRunTime());
break;
case FAILED:
case KILLED:
case OBSOLETE:
obsoleteMapOutput(event.getTaskAttemptId());
LOG.info("Ignoring obsolete output of " + event.getTaskStatus() +
" map-task: '" + event.getTaskAttemptId() + "'");
break;
case TIPFAILED:
tipFailed(event.getTaskAttemptId().getTaskID());
LOG.info("Ignoring output of failed map TIP: '" +
event.getTaskAttemptId() + "'");
break;
}
}
static URI getBaseURI(TaskAttemptID reduceId, String url) {
StringBuffer baseUrl = new StringBuffer(url);
if (!url.endsWith("/")) {
baseUrl.append("/");
}
baseUrl.append("mapOutput?job=");
baseUrl.append(reduceId.getJobID());
baseUrl.append("&reduce=");
baseUrl.append(reduceId.getTaskID().getId());
baseUrl.append("&map=");
URI u = URI.create(baseUrl.toString());
return u;
}
public synchronized void copySucceeded(TaskAttemptID mapId,
MapHost host,
long bytes,
long millis,
MapOutput<K,V> output
) throws IOException {
failureCounts.remove(mapId);
hostFailures.remove(host.getHostName());
int mapIndex = mapId.getTaskID().getId();
if (!finishedMaps[mapIndex]) {
output.commit();
finishedMaps[mapIndex] = true;
shuffledMapsCounter.increment(1);
if (--remainingMaps == 0) {
notifyAll();
}
// update the status
totalBytesShuffledTillNow += bytes;
updateStatus();
reduceShuffleBytes.increment(bytes);
lastProgressTime = System.currentTimeMillis();
LOG.debug("map " + mapId + " done " + status.getStateString());
}
}
private void updateStatus() {
float mbs = (float) totalBytesShuffledTillNow / (1024 * 1024);
int mapsDone = totalMaps - remainingMaps;
long secsSinceStart = (System.currentTimeMillis() - startTime) / 1000 + 1;
float transferRate = mbs / secsSinceStart;
progress.set((float) mapsDone / totalMaps);
String statusString = mapsDone + " / " + totalMaps + " copied.";
status.setStateString(statusString);
progress.setStatus("copy(" + mapsDone + " of " + totalMaps + " at "
+ mbpsFormat.format(transferRate) + " MB/s)");
}
public synchronized void copyFailed(TaskAttemptID mapId, MapHost host,
boolean readError, boolean connectExcpt) {
host.penalize();
int failures = 1;
if (failureCounts.containsKey(mapId)) {
IntWritable x = failureCounts.get(mapId);
x.set(x.get() + 1);
failures = x.get();
} else {
failureCounts.put(mapId, new IntWritable(1));
}
String hostname = host.getHostName();
if (hostFailures.containsKey(hostname)) {
IntWritable x = hostFailures.get(hostname);
x.set(x.get() + 1);
} else {
hostFailures.put(hostname, new IntWritable(1));
}
if (failures >= abortFailureLimit) {
try {
throw new IOException(failures + " failures downloading " + mapId);
} catch (IOException ie) {
reporter.reportException(ie);
}
}
checkAndInformJobTracker(failures, mapId, readError, connectExcpt);
checkReducerHealth();
long delay = (long) (INITIAL_PENALTY *
Math.pow(PENALTY_GROWTH_RATE, failures));
if (delay > maxDelay) {
delay = maxDelay;
}
penalties.add(new Penalty(host, delay));
failedShuffleCounter.increment(1);
}
public void reportLocalError(IOException ioe) {
try {
LOG.error("Shuffle failed : local error on this node: "
+ InetAddress.getLocalHost());
} catch (UnknownHostException e) {
LOG.error("Shuffle failed : local error on this node");
}
reporter.reportException(ioe);
}
// Notify the JobTracker
// after every read error, if 'reportReadErrorImmediately' is true or
// after every 'maxFetchFailuresBeforeReporting' failures
private void checkAndInformJobTracker(
int failures, TaskAttemptID mapId, boolean readError,
boolean connectExcpt) {
if (connectExcpt || (reportReadErrorImmediately && readError)
|| ((failures % maxFetchFailuresBeforeReporting) == 0)) {
LOG.info("Reporting fetch failure for " + mapId + " to jobtracker.");
status.addFetchFailedMap((org.apache.hadoop.mapred.TaskAttemptID) mapId);
}
}
private void checkReducerHealth() {
final float MAX_ALLOWED_FAILED_FETCH_ATTEMPT_PERCENT = 0.5f;
final float MIN_REQUIRED_PROGRESS_PERCENT = 0.5f;
final float MAX_ALLOWED_STALL_TIME_PERCENT = 0.5f;
long totalFailures = failedShuffleCounter.getValue();
int doneMaps = totalMaps - remainingMaps;
boolean reducerHealthy =
(((float)totalFailures / (totalFailures + doneMaps))
< MAX_ALLOWED_FAILED_FETCH_ATTEMPT_PERCENT);
// check if the reducer has progressed enough
boolean reducerProgressedEnough =
(((float)doneMaps / totalMaps)
>= MIN_REQUIRED_PROGRESS_PERCENT);
// check if the reducer is stalled for a long time
// duration for which the reducer is stalled
int stallDuration =
(int)(System.currentTimeMillis() - lastProgressTime);
// duration for which the reducer ran with progress
int shuffleProgressDuration =
(int)(lastProgressTime - startTime);
// min time the reducer should run without getting killed
int minShuffleRunDuration =
Math.max(shuffleProgressDuration, maxMapRuntime);
boolean reducerStalled =
(((float)stallDuration / minShuffleRunDuration)
>= MAX_ALLOWED_STALL_TIME_PERCENT);
// kill if not healthy and has insufficient progress
if ((failureCounts.size() >= maxFailedUniqueFetches ||
failureCounts.size() == (totalMaps - doneMaps))
&& !reducerHealthy
&& (!reducerProgressedEnough || reducerStalled)) {
LOG.fatal("Shuffle failed with too many fetch failures " +
"and insufficient progress!");
String errorMsg = "Exceeded MAX_FAILED_UNIQUE_FETCHES; bailing-out.";
reporter.reportException(new IOException(errorMsg));
}
}
public synchronized void tipFailed(TaskID taskId) {
if (!finishedMaps[taskId.getId()]) {
finishedMaps[taskId.getId()] = true;
if (--remainingMaps == 0) {
notifyAll();
}
updateStatus();
}
}
public synchronized void addKnownMapOutput(String hostName,
String hostUrl,
TaskAttemptID mapId) {
MapHost host = mapLocations.get(hostName);
if (host == null) {
host = new MapHost(hostName, hostUrl);
mapLocations.put(hostName, host);
}
host.addKnownMap(mapId);
// Mark the host as pending
if (host.getState() == State.PENDING) {
pendingHosts.add(host);
notifyAll();
}
}
public synchronized void obsoleteMapOutput(TaskAttemptID mapId) {
obsoleteMaps.add(mapId);
}
public synchronized void putBackKnownMapOutput(MapHost host,
TaskAttemptID mapId) {
host.addKnownMap(mapId);
}
public synchronized MapHost getHost() throws InterruptedException {
while(pendingHosts.isEmpty()) {
wait();
}
MapHost host = null;
Iterator<MapHost> iter = pendingHosts.iterator();
int numToPick = random.nextInt(pendingHosts.size());
for (int i=0; i <= numToPick; ++i) {
host = iter.next();
}
pendingHosts.remove(host);
host.markBusy();
LOG.info("Assigning " + host + " with " + host.getNumKnownMapOutputs() +
" to " + Thread.currentThread().getName());
shuffleStart.set(System.currentTimeMillis());
return host;
}
public synchronized List<TaskAttemptID> getMapsForHost(MapHost host) {
List<TaskAttemptID> list = host.getAndClearKnownMaps();
Iterator<TaskAttemptID> itr = list.iterator();
List<TaskAttemptID> result = new ArrayList<TaskAttemptID>();
int includedMaps = 0;
int totalSize = list.size();
// find the maps that we still need, up to the limit
while (itr.hasNext()) {
TaskAttemptID id = itr.next();
if (!obsoleteMaps.contains(id) && !finishedMaps[id.getTaskID().getId()]) {
result.add(id);
if (++includedMaps >= MAX_MAPS_AT_ONCE) {
break;
}
}
}
// put back the maps left after the limit
while (itr.hasNext()) {
TaskAttemptID id = itr.next();
if (!obsoleteMaps.contains(id) && !finishedMaps[id.getTaskID().getId()]) {
host.addKnownMap(id);
}
}
LOG.info("assigned " + includedMaps + " of " + totalSize + " to " +
host + " to " + Thread.currentThread().getName());
return result;
}
public synchronized void freeHost(MapHost host) {
if (host.getState() != State.PENALIZED) {
if (host.markAvailable() == State.PENDING) {
pendingHosts.add(host);
notifyAll();
}
}
LOG.info(host + " freed by " + Thread.currentThread().getName() + " in " +
(System.currentTimeMillis()-shuffleStart.get()) + "ms");
}
public synchronized void resetKnownMaps() {
mapLocations.clear();
obsoleteMaps.clear();
pendingHosts.clear();
}
/**
* Wait until the shuffle finishes or until the timeout.
* @param millis maximum wait time
* @return true if the shuffle is done
* @throws InterruptedException
*/
@Override
public synchronized boolean waitUntilDone(int millis
) throws InterruptedException {
if (remainingMaps > 0) {
wait(millis);
return remainingMaps == 0;
}
return true;
}
/**
* A structure that records the penalty for a host.
*/
private static class Penalty implements Delayed {
MapHost host;
private long endTime;
Penalty(MapHost host, long delay) {
this.host = host;
this.endTime = System.currentTimeMillis() + delay;
}
@Override
public long getDelay(TimeUnit unit) {
long remainingTime = endTime - System.currentTimeMillis();
return unit.convert(remainingTime, TimeUnit.MILLISECONDS);
}
@Override
public int compareTo(Delayed o) {
long other = ((Penalty) o).endTime;
return endTime == other ? 0 : (endTime < other ? -1 : 1);
}
}
/**
* A thread that takes hosts off of the penalty list when the timer expires.
*/
private class Referee extends Thread {
public Referee() {
setName("ShufflePenaltyReferee");
setDaemon(true);
}
public void run() {
try {
while (true) {
// take the first host that has an expired penalty
MapHost host = penalties.take().host;
synchronized (ShuffleSchedulerImpl.this) {
if (host.markAvailable() == MapHost.State.PENDING) {
pendingHosts.add(host);
ShuffleSchedulerImpl.this.notifyAll();
}
}
}
} catch (InterruptedException ie) {
return;
} catch (Throwable t) {
reporter.reportException(t);
}
}
}
@Override
public void close() throws InterruptedException {
referee.interrupt();
referee.join();
}
}