/**
* 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.URI;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.mapred.MapTaskCompletionEventsUpdate;
import org.apache.hadoop.mapred.TaskCompletionEvent;
import org.apache.hadoop.mapred.TaskUmbilicalProtocol;
import org.apache.hadoop.mapreduce.TaskAttemptID;
class EventFetcher<K,V> extends Thread {
private static final long SLEEP_TIME = 1000;
private static final int MAX_RETRIES = 10;
private static final int RETRY_PERIOD = 5000;
private static final Log LOG = LogFactory.getLog(EventFetcher.class);
private final TaskAttemptID reduce;
private final TaskUmbilicalProtocol umbilical;
private final ShuffleScheduler<K,V> scheduler;
private int fromEventIdx = 0;
private int maxEventsToFetch;
private ExceptionReporter exceptionReporter = null;
private int maxMapRuntime = 0;
private volatile boolean stopped = false;
public EventFetcher(TaskAttemptID reduce,
TaskUmbilicalProtocol umbilical,
ShuffleScheduler<K,V> scheduler,
ExceptionReporter reporter,
int maxEventsToFetch) {
setName("EventFetcher for fetching Map Completion Events");
setDaemon(true);
this.reduce = reduce;
this.umbilical = umbilical;
this.scheduler = scheduler;
exceptionReporter = reporter;
this.maxEventsToFetch = maxEventsToFetch;
}
@Override
public void run() {
int failures = 0;
LOG.info(reduce + " Thread started: " + getName());
try {
while (!stopped && !Thread.currentThread().isInterrupted()) {
try {
int numNewMaps = getMapCompletionEvents();
failures = 0;
if (numNewMaps > 0) {
LOG.info(reduce + ": " + "Got " + numNewMaps + " new map-outputs");
}
LOG.debug("GetMapEventsThread about to sleep for " + SLEEP_TIME);
if (!Thread.currentThread().isInterrupted()) {
Thread.sleep(SLEEP_TIME);
}
} catch (InterruptedException e) {
LOG.info("EventFetcher is interrupted.. Returning");
return;
} catch (IOException ie) {
LOG.info("Exception in getting events", ie);
// check to see whether to abort
if (++failures >= MAX_RETRIES) {
throw new IOException("too many failures downloading events", ie);
}
// sleep for a bit
if (!Thread.currentThread().isInterrupted()) {
Thread.sleep(RETRY_PERIOD);
}
}
}
} catch (InterruptedException e) {
return;
} catch (Throwable t) {
exceptionReporter.reportException(t);
return;
}
}
public void shutDown() {
this.stopped = true;
interrupt();
try {
join(5000);
} catch(InterruptedException ie) {
LOG.warn("Got interrupted while joining " + getName(), ie);
}
}
/**
* Queries the {@link TaskTracker} for a set of map-completion events
* from a given event ID.
* @throws IOException
*/
protected int getMapCompletionEvents() throws IOException {
int numNewMaps = 0;
TaskCompletionEvent events[] = null;
do {
MapTaskCompletionEventsUpdate update =
umbilical.getMapCompletionEvents(
(org.apache.hadoop.mapred.JobID)reduce.getJobID(),
fromEventIdx,
maxEventsToFetch,
(org.apache.hadoop.mapred.TaskAttemptID)reduce);
events = update.getMapTaskCompletionEvents();
LOG.debug("Got " + events.length + " map completion events from " +
fromEventIdx);
// Check if the reset is required.
// Since there is no ordering of the task completion events at the
// reducer, the only option to sync with the new jobtracker is to reset
// the events index
if (update.shouldReset()) {
fromEventIdx = 0;
scheduler.resetKnownMaps();
}
// Update the last seen event ID
fromEventIdx += events.length;
// Process the TaskCompletionEvents:
// 1. Save the SUCCEEDED maps in knownOutputs to fetch the outputs.
// 2. Save the OBSOLETE/FAILED/KILLED maps in obsoleteOutputs to stop
// fetching from those maps.
// 3. Remove TIPFAILED maps from neededOutputs since we don't need their
// outputs at all.
for (TaskCompletionEvent event : events) {
switch (event.getTaskStatus()) {
case SUCCEEDED:
URI u = getBaseURI(event.getTaskTrackerHttp());
scheduler.addKnownMapOutput(u.getHost() + ":" + u.getPort(),
u.toString(),
event.getTaskAttemptId());
numNewMaps ++;
int duration = event.getTaskRunTime();
if (duration > maxMapRuntime) {
maxMapRuntime = duration;
scheduler.informMaxMapRunTime(maxMapRuntime);
}
break;
case FAILED:
case KILLED:
case OBSOLETE:
scheduler.obsoleteMapOutput(event.getTaskAttemptId());
LOG.info("Ignoring obsolete output of " + event.getTaskStatus() +
" map-task: '" + event.getTaskAttemptId() + "'");
break;
case TIPFAILED:
scheduler.tipFailed(event.getTaskAttemptId().getTaskID());
LOG.info("Ignoring output of failed map TIP: '" +
event.getTaskAttemptId() + "'");
break;
}
}
} while (events.length == maxEventsToFetch);
return numNewMaps;
}
private URI getBaseURI(String url) {
StringBuffer baseUrl = new StringBuffer(url);
if (!url.endsWith("/")) {
baseUrl.append("/");
}
baseUrl.append("mapOutput?job=");
baseUrl.append(reduce.getJobID());
baseUrl.append("&reduce=");
baseUrl.append(reduce.getTaskID().getId());
baseUrl.append("&map=");
URI u = URI.create(baseUrl.toString());
return u;
}
}